Immune Response of Aquatic Organisms

Immune Response of Aquatic Immune Response of Aquatic OrganismsOrganisms

Preliminary ConceptsPreliminary Concepts Disease problems have grown proportionally Disease problems have grown proportionally

with the intensive or expansive culture of with the intensive or expansive culture of aquaculture speciesaquaculture species

Why?Why?1)1) Increased stocking densities (lower profit margins)Increased stocking densities (lower profit margins)2)2) Infected carriers (largely broodstock)Infected carriers (largely broodstock)3)3) Infected facilities (GMPs being followed?)Infected facilities (GMPs being followed?)4)4) Poor nutrition (we are way behind)Poor nutrition (we are way behind)5)5) Substandard water quality (traditional)Substandard water quality (traditional)

Biggest problemBiggest problem: : greater susceptibility via greater susceptibility via weakening of resistance under intensive culture weakening of resistance under intensive culture conditionsconditions

The Immune The Immune ResponseResponse

For fish, response to a foreign agent is rather similar to For fish, response to a foreign agent is rather similar to that of mammals; shrimp, very rudimentarythat of mammals; shrimp, very rudimentary

Response can be highly specific (a specific antibody for Response can be highly specific (a specific antibody for a specific antigen) is known as the a specific antigen) is known as the immune responseimmune response..

The immune system “scans” the body to identify any The immune system “scans” the body to identify any substance (natural/synthetic or living/inert) that it substance (natural/synthetic or living/inert) that it considers foreignconsiders foreign

Differentiates between “self” and “non-self”Differentiates between “self” and “non-self” Works with several types of white blood cells, located Works with several types of white blood cells, located

throughout the body, that work together in a highly throughout the body, that work together in a highly integrated wayintegrated way

DefinitionsDefinitions resistanceresistance: any type of barrier within the : any type of barrier within the

host that allows it to resist the pathogenhost that allows it to resist the pathogen innate or natural immunityinnate or natural immunity: attributed to : attributed to

inherited ability to produce antibodies inherited ability to produce antibodies without stimulation by antigenswithout stimulation by antigens

acquired immunityacquired immunity: host is stimulated by : host is stimulated by contact with antigens contact with antigens

passive immunitypassive immunity: acquired through the : acquired through the use of antibodies from other animals use of antibodies from other animals (vaccination)(vaccination)

we will add another term today, we will add another term today, tolerancetolerance

Immune Immune ResponsRespons

e e SystemSystem

Made up of two cellular systems: Made up of two cellular systems: 1) cell-mediated immunity 1) cell-mediated immunity (T cells)(T cells) and and 2) humoral antibody system (B cells)2) humoral antibody system (B cells)

Both work by identifying antigens (foreign proteins or Both work by identifying antigens (foreign proteins or glycoproteins)glycoproteins)

Immune Response Immune Response Sequence: Sequence: 11

Begins when Begins when macrophagemacrophage encounters this non-encounters this non-self entity (e.g., virus): self entity (e.g., virus): macrophage literally macrophage literally “eats” the substance, “eats” the substance, digests it and displays digests it and displays pieces of the invader pieces of the invader on its surface. These on its surface. These pieces are pieces are antigensantigens..

Meanwhile, other viral Meanwhile, other viral particles are at work, particles are at work, infecting nearby infecting nearby host host cellscells..

Source: Cancer Research Institute (2002) www.cancerresearch.org/immhow.html


Antigenic fragments Antigenic fragments alert a specific type alert a specific type of T lymphocyte of T lymphocyte (“helper” T(“helper” T) to begin ) to begin choreographed choreographed attack of intruderattack of intruder

Helper recognizes Helper recognizes antigen particles antigen particles and binds to the and binds to the macrophage via an macrophage via an antigen receptorantigen receptor

Helper T cells are unique Helper T cells are unique to a specific antigento a specific antigen


This binding stimulates This binding stimulates production of production of chemical substances chemical substances such as such as interleukin-1interleukin-1 (IL-1), (IL-1), tumor tumor necrosis factornecrosis factor (TNF) (TNF) by macrophageby macrophage

Helper T cells generates Helper T cells generates interleukin-2interleukin-2 and and gamma interferongamma interferon (IFN-y)(IFN-y)

All substances facilitate All substances facilitate intercellular intercellular communicationcommunication

Astonishing SynchronizationAstonishing Synchronization TNF steps up production of IL-1, it also TNF steps up production of IL-1, it also

causes fever in homeothermscauses fever in homeotherms TNF and IL-1 are TNF and IL-1 are cytokinescytokines (cellular) (cellular) IL-1 also causes fever but additionally IL-1 also causes fever but additionally

forms immune cell clusters and stimulates forms immune cell clusters and stimulates the helper T cell to release IL-2the helper T cell to release IL-2

IL-2 causes T cells to release gamma IL-2 causes T cells to release gamma interferon which, in-turn, activates interferon which, in-turn, activates macrophagesmacrophages

IL-2 also instructs other helper T cells and IL-2 also instructs other helper T cells and “killer” T cells“killer” T cells to multiply to multiply


As mentioned IL-2 instructs As mentioned IL-2 instructs helper T’s and helper T’s and “killer T’s”“killer T’s” to multiplyto multiply

Proliferating helper T’s release Proliferating helper T’s release substances that cause substances that cause B B cellscells (another type of (another type of lymphocyte) to multiply lymphocyte) to multiply and produce and produce antibodiesantibodies

Meanwhile, many invader cells Meanwhile, many invader cells have been consumed by have been consumed by macrophages, but other macrophages, but other “daughter” viral particles “daughter” viral particles have escaped and are have escaped and are infecting other cellsinfecting other cells


Killer T cells start shooting Killer T cells start shooting “holes” in the surface of “holes” in the surface of infected host cellsinfected host cells

Antibodies released by B cells Antibodies released by B cells bind in a lock-and-key bind in a lock-and-key fashion to antigens on the fashion to antigens on the surface of invaders that surface of invaders that have escaped macrophages have escaped macrophages ((Ag-Ab complexAg-Ab complex).).

Makes it easier for macrophages Makes it easier for macrophages and special killer and special killer lymphocytes to destroy lymphocytes to destroy unwelcomed entities.unwelcomed entities.

Binding of antibodies with Binding of antibodies with antigens signals release of antigens signals release of a blood component, a blood component, complementcomplement, to puncture , to puncture virus membrane (death)virus membrane (death)


Finally, as the infection is Finally, as the infection is brought under control, brought under control, yet another type of T cell, yet another type of T cell, the the suppressor T cellsuppressor T cell, , tells B cells, helper T’s tells B cells, helper T’s and killer T’s to turn offand killer T’s to turn off

Most immune cells die, but a Most immune cells die, but a few remain in the body, few remain in the body, called called memory cellsmemory cells

They will be able to respond They will be able to respond more quickly the next more quickly the next time the body is invaded time the body is invaded by the same foreign by the same foreign substancesubstance

Immune Response in FishImmune Response in Fish REM: aquaculture = 25% of world fish productionREM: aquaculture = 25% of world fish production More fish means deterioration in culture More fish means deterioration in culture

environment, and increased incidence of diseaseenvironment, and increased incidence of disease Poor water quality affects the fish immune Poor water quality affects the fish immune

system in a negative waysystem in a negative way The status of beingThe status of being immune immune is “an inherited is “an inherited

ability to resist infection” (Shoemaker et al., ability to resist infection” (Shoemaker et al., 2000)2000)

i.e., recognition of “non-self” or a foreign agent, i.e., recognition of “non-self” or a foreign agent, with subsequent response and memory in with subsequent response and memory in vertebratesvertebrates

Immune Response in FishImmune Response in Fish Fish are the most primitive vertebrates, but had to Fish are the most primitive vertebrates, but had to

develop an immune system for protectiondevelop an immune system for protection the only exception was cold water species: due to the only exception was cold water species: due to

low bacterial generation time at lower temperatureslow bacterial generation time at lower temperatures those living under schooling conditions and in warm those living under schooling conditions and in warm

environments needed a highly developed responseenvironments needed a highly developed response all fish pathogens contain all fish pathogens contain antigensantigens: viral particles, : viral particles,

bacteria, fungi, toxins and animal parasitesbacteria, fungi, toxins and animal parasites

Immune Response in FishImmune Response in Fish• Immune response in fish includesImmune response in fish includes: :

• expansionexpansion of cells for the immune response of cells for the immune response• expressionexpression of the cells and molecules (e.g., antibody) of the cells and molecules (e.g., antibody)• coordinationcoordination of the response by regulatory of the response by regulatory

substancessubstances

• Fish immunology is a young science!Fish immunology is a young science!

• Early work was largely comparative, now focuses on Early work was largely comparative, now focuses on understanding how immune system responds to understanding how immune system responds to foreign agents or how innate resistance can be foreign agents or how innate resistance can be selected for by breeding programsselected for by breeding programs

Response of Fish Following Response of Fish Following an Encounter with a an Encounter with a

PathogenPathogenFish Contacts Pathogen

Innate Immunity

Failure (Disease / Death) Initiation and Instruction of the Specific Immune Response

Success (No Disease or Infection)

Humoral Response (Extracellular Pathogens and Toxins)

Cell-Mediated Immune Response (Intracellular Pathogens and Viruses)

Acquired Immunity, Immunologic Memory, and Protection (Survival)

Immune Tissues and Immune Tissues and OrgansOrgans

Most important Most important immunocompetentimmunocompetent organs: organs: thymus, kidney (head, trunk), spleen and liverthymus, kidney (head, trunk), spleen and liver

Immune tissues in these organs not well Immune tissues in these organs not well defined (Manning, 1994)defined (Manning, 1994)

ThymusThymus: develops T-lymphocytes (helpers, : develops T-lymphocytes (helpers, killers; similar to other vert’s), indirect evidence killers; similar to other vert’s), indirect evidence

KidneyKidney: important in both immunity and : important in both immunity and hematopoiesis, site of blood cell differentiationhematopoiesis, site of blood cell differentiation– Early immune response handled by entire kidneyEarly immune response handled by entire kidney– With maturity, anterior used for immune response; With maturity, anterior used for immune response;

posterior for blood filtration, urinary activitiesposterior for blood filtration, urinary activities


KidneyKidney (cont.): (cont.): – blood flows slowly through kidney and antigens blood flows slowly through kidney and antigens

are “trapped” or exposed to reticular cells, are “trapped” or exposed to reticular cells, macrophages, lymphocytesmacrophages, lymphocytes

– Anterior is where “memory” occurs (Secombs et Anterior is where “memory” occurs (Secombs et al., 1982)al., 1982)

SpleenSpleen: secondary to kidney, involved in : secondary to kidney, involved in immune reactivity and blood cell formation, immune reactivity and blood cell formation, contains lymphocytes and macrophagescontains lymphocytes and macrophages

LiverLiver: could be involved in production of : could be involved in production of components of the complement cascade, components of the complement cascade, important in resistance; not real clearimportant in resistance; not real clear


Mucus and skinMucus and skin: natural barriers, has : natural barriers, has molecules with immune actions:molecules with immune actions:– LysozymeLysozyme– ComplementComplement– Natural antibodies (Ab) and immunoglobulins (Ig)Natural antibodies (Ab) and immunoglobulins (Ig)– Specific antibodies tentatively reported in mucus Specific antibodies tentatively reported in mucus

of of Ictalurus punctatusIctalurus punctatus (Lobb, 1987); (Lobb, 1987); Oncorhyncus Oncorhyncus mykissmykiss (St. Louis-Cormier et al., 1984) (St. Louis-Cormier et al., 1984)

– Zilberg and Klesius, 1997) showed mucus Zilberg and Klesius, 1997) showed mucus immunoglobulin elevated in immunoglobulin elevated in II. . punctatuspunctatus after after exposure to bacteriaexposure to bacteria

A: Natural Immunity and A: Natural Immunity and Disease ResistanceDisease Resistance

1)1) Non-specific immune cellsNon-specific immune cells• Monocytes and tissue macrophagesMonocytes and tissue macrophages: most important : most important

cells in immune response, produce cells in immune response, produce cytokinescytokines (Clem et al., (Clem et al., 1985), primary cells involved in phagocytosis and first 1985), primary cells involved in phagocytosis and first killing of pathogens upon first recognition and subsequent killing of pathogens upon first recognition and subsequent infection (Shoemaker et al.,1997)infection (Shoemaker et al.,1997)

• NeutrophilsNeutrophils: primary cells in early stages of : primary cells in early stages of inflammation (Manning, 1994), neutrophils produce inflammation (Manning, 1994), neutrophils produce cytokines to recruit immune cells to damaged or infected cytokines to recruit immune cells to damaged or infected area; neutrophils are phagocytic in area; neutrophils are phagocytic in I. punctatusI. punctatus, kill , kill bacteria by extracellular mechanismsbacteria by extracellular mechanisms

• Natural killer cellsNatural killer cells: use receptor binding to target cells : use receptor binding to target cells and lyse them; important in parasitic and viral immunityand lyse them; important in parasitic and viral immunity

Natural Immunity and Disease Natural Immunity and Disease ResistanceResistance

2)2) Phagocytosis (cell eating)Phagocytosis (cell eating): most primitive : most primitive of defense mechanisms, occurs in stagesof defense mechanisms, occurs in stages

Movement by Movement by chemotaxischemotaxis (directional) or (directional) or chemokinesischemokinesis (non-d) of phagocytes in (non-d) of phagocytes in response to foreign objectresponse to foreign object

Attachment via Attachment via lectins (sugars)lectins (sugars) Engulfment of the foreign agent (simple Engulfment of the foreign agent (simple

movement into the phagocyte)movement into the phagocyte) Killing and digestionKilling and digestion

• Oxygen-independent mechanisms: low pH, Oxygen-independent mechanisms: low pH, lysozyme, lactoferrin, proteolytic/hydrolytic enzymeslysozyme, lactoferrin, proteolytic/hydrolytic enzymes

• Oxygen dependent mechanismsOxygen dependent mechanisms

http://en.wikipedia.org/wiki/Image:Hemagglutinin_lateral.jpg

Natural Immunity and Disease Natural Immunity and Disease ResistanceResistance

3)3) Nonspecific Humoral MoleculesNonspecific Humoral Molecules: : MoleculeMolecule CompositionComposition Mode of ActionMode of Action

LectinsLectins Specific sugar-binding Specific sugar-binding proteinsproteins

Recognition, Recognition, precipitation, precipitation, agglutinationagglutination

Lytic enzymesLytic enzymes Catalytic proteins Catalytic proteins lysozyme, etc.lysozyme, etc.

Hemolytic and Hemolytic and antibacterial activityantibacterial activity

Transferrin/lactoferrinTransferrin/lactoferrin GlycoproteinGlycoprotein Iron bindingIron binding

CeruloplasminCeruloplasmin Acute-phase proteinAcute-phase protein Copper bindingCopper binding

C-reactive proteinC-reactive protein Acute-phase proteinAcute-phase protein Activation of Activation of complementcomplement

InterferonInterferon proteinprotein Resistance to viral Resistance to viral infectioninfection

Natural Immunity and Natural Immunity and Disease ResistanceDisease Resistance

• Lytic enzymes Lytic enzymes are antibacterial molecules that are antibacterial molecules that cleave the bacterial cell walls cleave the bacterial cell walls (Specifically at (Specifically at 1,4 1,4 linkages of n-acetyl muramic and n-acetyl glucosamine).linkages of n-acetyl muramic and n-acetyl glucosamine).

• LysozymeLysozyme (another enzyme) helps destroy (another enzyme) helps destroy Gram-positive bacteria, and breaks cell walls Gram-positive bacteria, and breaks cell walls (complement) on Gram-negative(complement) on Gram-negative

• Acute-phase proteins Acute-phase proteins are serum proteins: are serum proteins: ceruloplasmin responsible for binding of copper, ceruloplasmin responsible for binding of copper, usually generated as the result of stressusually generated as the result of stress

• Nutrition also influences levels of C-reactive Nutrition also influences levels of C-reactive protein protein (yet another link to the importance of nutrition and disease (yet another link to the importance of nutrition and disease prevention).prevention).

http://upload.wikimedia.org/wikipedia/commons/a/ab/CRP_pretty.png

Natural Immunity and Natural Immunity and Disease ResistanceDisease Resistance

4)4) ComplementComplement:: consists of 20 or more chemically consists of 20 or more chemically different serum proteins + glycoproteins having different serum proteins + glycoproteins having enzyme functionenzyme function

originally named “complement” because it was originally named “complement” because it was considered a biological substance considered a biological substance complementingcomplementing the the action of antibodyaction of antibody

Instead, antibodies actually activate a series of Instead, antibodies actually activate a series of reactions in serum known as the “reactions in serum known as the “complement complement cascadecascade.”.”

interacts with either a specific antibody, or acts non-interacts with either a specific antibody, or acts non-specifically on surface molecules of bacteria, viruses specifically on surface molecules of bacteria, viruses and parasites; both pathways exist in fish (Sakai, 1992)and parasites; both pathways exist in fish (Sakai, 1992)

ActionAction: clears antigenic molecules, immune : clears antigenic molecules, immune complexes, participates in inflammation and complexes, participates in inflammation and phagocytosisphagocytosis

B: Humoral Immunity in B: Humoral Immunity in FishFish

DefinedDefined:: the antibody response to foreign the antibody response to foreign antigensantigens

Fish posses B-cells (surface immunoglobulin-Fish posses B-cells (surface immunoglobulin-positive cells), similar to mammals in structurepositive cells), similar to mammals in structure

Surface IgM of B-cells serves as receptor for Surface IgM of B-cells serves as receptor for antigen recognition and is of same specificity as antigen recognition and is of same specificity as the antibody molecule that will be produced the antibody molecule that will be produced (Janeway and Travers, 1994)(Janeway and Travers, 1994)

Unlike crustaceans, fish possess immunologic Unlike crustaceans, fish possess immunologic memory (Arkoosh and Kaattari, 1991)memory (Arkoosh and Kaattari, 1991)

Their primary and memory response both use the Their primary and memory response both use the same IgM molecule, with eight antigen binding same IgM molecule, with eight antigen binding sites, a potent activator of complementsites, a potent activator of complement

C: Cell-Mediated C: Cell-Mediated Immunity in FishImmunity in Fish

Used to Used to eliminate intracellular pathogens eliminate intracellular pathogens (e.g., (e.g., bacteria, virus, parasites)bacteria, virus, parasites)

Relies on contact of the foreign invader with the Relies on contact of the foreign invader with the subsequent presentation of an antigen having the subsequent presentation of an antigen having the same major histocompatability complex same major histocompatability complex (MHC I or (MHC I or II) to T-helper cells (REM?) II) to T-helper cells (REM?)

Once T-helper cells are stimulated, the produce Once T-helper cells are stimulated, the produce cytokines that result in stimulation of cytokines that result in stimulation of effectoreffector cellscells (cytotoxic lymphocytes) or macrophages (cytotoxic lymphocytes) or macrophages

Cytokines stimulate aforementioned cells and also Cytokines stimulate aforementioned cells and also recruit new cells to the area, activate themrecruit new cells to the area, activate them

Work quite well against bacteria, important Work quite well against bacteria, important against against Edwardsiella ictaluri Edwardsiella ictaluri (Shoemaker, et al., (Shoemaker, et al., 1999)1999)

What Influences Fish What Influences Fish Immune Systems??Immune Systems??

Factors Influencing Disease Factors Influencing Disease Resistance and Immune Response of Resistance and Immune Response of

FishFish11

GeneralGeneral SpecificSpecificGeneticsGenetics Individuals may exhibit differences in innate Individuals may exhibit differences in innate

resistance and acquired immunityresistance and acquired immunity

EnvironmeEnvironmentnt

Temperature, season, photoperiodTemperature, season, photoperiod

StressStress Water quality, pollution, density, handling and Water quality, pollution, density, handling and transport, breeding cyclestransport, breeding cycles

NutritionNutrition Feed quality and quantity, nutrient Feed quality and quantity, nutrient availability, use of immunostimulants, availability, use of immunostimulants, antinutritional factors in feedsantinutritional factors in feeds

FishFish Age, species or strains, individualsAge, species or strains, individuals

PathogenPathogen Exposure levels, type (parasite, bacterial, Exposure levels, type (parasite, bacterial, viral), virulenceviral), virulence

1From Shoemaker et al.,2001. Immunity and disease resistance in fish. In: Nutrition and Fish Health (Ed.: Lim, C., Webster, C.D.). Food Products Press, NY. Pgs 149-162.

Factors Affecting Immune Factors Affecting Immune Response: Response: temperaturetemperature

Resting fish body temperature is near Resting fish body temperature is near ambientambient

pathogen generation time is temperature pathogen generation time is temperature dependentdependent

fishes living in cold temperatures have little fishes living in cold temperatures have little need for an immune responseneed for an immune response

coldwater fishes do not produce coldwater fishes do not produce immunoglobulinsimmunoglobulins

immune response slower at cold immune response slower at cold temperatures (up to 28 days!)temperatures (up to 28 days!)

Factors Affecting Immune Factors Affecting Immune Response: Response: ageage

Immune competency develops Immune competency develops relatively slowly in animalsrelatively slowly in animals

mammals obtain antibodies through mammals obtain antibodies through mother’s milk for up to six weeksmother’s milk for up to six weeks

not the case with fishnot the case with fish rainbow trout are found to be immune rainbow trout are found to be immune

competent at an early age (0.3g)competent at an early age (0.3g) significancesignificance: immunization of very : immunization of very

young fish is practicalyoung fish is practical

Passive Immunity: Passive Immunity: vaccinationvaccination

Most immunizing substances developed Most immunizing substances developed for fish have been for fish have been bacterinsbacterins

these are killed, whole-cell suspensions these are killed, whole-cell suspensions of pathogenic bacteriaof pathogenic bacteria

some practical viral vaccines exist (e.g., some practical viral vaccines exist (e.g., CCV)CCV)

probably will take place through probably will take place through injection of avirulent viral strainsinjection of avirulent viral strains

immunization against animal parasites immunization against animal parasites might also eventually be possiblemight also eventually be possible

Duration of Passive Duration of Passive ImmunityImmunity

Typical response is of short durationTypical response is of short duration very dependent upon environmental very dependent upon environmental

temperaturetemperature primary response to injection is usually only primary response to injection is usually only

a few weeksa few weeks secondary injections nine weeks after secondary injections nine weeks after

primary have resulted in maintenance of primary have resulted in maintenance of protective antibody protective antibody titerstiters, as in higher , as in higher animalsanimals

Part 2:Part 2: Immune Response Immune Response in Shrimpin Shrimp

As mentioned, fish and shrimp differ As mentioned, fish and shrimp differ significantly in their ability and degree to significantly in their ability and degree to which they carry out this responsewhich they carry out this response

the capacity to recognize, expand the specific the capacity to recognize, expand the specific recognition, express specific recognition, and recognition, express specific recognition, and coordinate defense is much lower in shrimpcoordinate defense is much lower in shrimp

mistakemistake: often drug manufacturers and : often drug manufacturers and scientists assume that fish and shrimp have scientists assume that fish and shrimp have the same the same immune competencyimmune competency

thus, inappropriate decisions have been thus, inappropriate decisions have been made on how defense mechanisms might be made on how defense mechanisms might be enhanced in shrimpenhanced in shrimp

Immunoreactive Immunoreactive Molecules of the ShrimpMolecules of the Shrimp Shrimp blood is known as Shrimp blood is known as hemolymphhemolymph it contains both oxygen-carrying molecules it contains both oxygen-carrying molecules

((hemocyaninhemocyanin) and immunoreactive molecules ) and immunoreactive molecules known as known as lectinslectins

lectins are glycoproteins (sugar + protein) that lectins are glycoproteins (sugar + protein) that bind with the sugar portion of other molecules, bind with the sugar portion of other molecules, particularly foreign onesparticularly foreign ones

these lectins have broad specificity, meaning these lectins have broad specificity, meaning they will bind with a broad range of other they will bind with a broad range of other molecules, not just sugarsmolecules, not just sugars

for example, they can bind with the sugar for example, they can bind with the sugar moeity of lipopolysaccharides, or moeity of lipopolysaccharides, or beta-beta-glucansglucans

Immunoreactive Immunoreactive Molecules in ShrimpMolecules in Shrimp

Gram negative bacteria (e.g., Gram negative bacteria (e.g., Vibrio sp.Vibrio sp.) ) and yeasts which contain beta-glucans can be recognized by lectins

they also happen to recognize viruses and other infectious agents with surface glycoproteins

after recognizing the foreign agent, the lectin will agglutinize (clump) it, rendering it ineffective

the specificity for binding by a lectin cannot be increased as with antibodies


The only way the immune response in shrimp can be The only way the immune response in shrimp can be enhanced is by putting more lectins in the enhanced is by putting more lectins in the bloodstreambloodstream

after the infection is over, the after the infection is over, the cells that produce cells that produce lectins completely lectins completely lack the ability to remember the lack the ability to remember the infectious agent...oops!!!infectious agent...oops!!!

soso, immune response in shrimp is , immune response in shrimp is notnot an acquired one an acquired one another characteristic of lectins is that once bound to another characteristic of lectins is that once bound to

a sugar on the foreign agent, the complex is easily a sugar on the foreign agent, the complex is easily phagocitizedphagocitized

the phagocytic cell is known as the phagocytic cell is known as hemocytehemocyte

Shrimp Hemocyte Shrimp Hemocyte ResponseResponse

As mentioned, the primary defense cells in As mentioned, the primary defense cells in shrimp are called shrimp are called hemocyteshemocytes

certain hemocytes have the ability to certain hemocytes have the ability to phagocytize foreign cells, others to encapsulate phagocytize foreign cells, others to encapsulate and render agents ineffectiveand render agents ineffective

the defense mechanisms of shrimp are thus more the defense mechanisms of shrimp are thus more primitive and singular in their ability to control primitive and singular in their ability to control infectioninfection

this means that this means that stress is more likely to negatively stress is more likely to negatively impact shrimp defenses against infectionimpact shrimp defenses against infection

no backup systems available when primary no backup systems available when primary system fails!!system fails!!


blocking attachment by use of drugs blocking attachment by use of drugs or diets containing beta-glucans or diets containing beta-glucans might prevent the binding of foreign might prevent the binding of foreign agentsagents

along with lectins, shrimp have along with lectins, shrimp have lysozymelysozyme, an anti-bacterial enzyme, an anti-bacterial enzyme

lipolytic enzymes against viruseslipolytic enzymes against viruses

A Brief History of Shrimp A Brief History of Shrimp ImmunologyImmunology

Bacteria and fungi are dealt with by Bacteria and fungi are dealt with by appropriate measures (e.g., similar for appropriate measures (e.g., similar for most aquaculture animals)most aquaculture animals)

Most work Most work hashas dealt with bacterial dealt with bacterial pathogenspathogens

Relatively few parasites: cuticular Relatively few parasites: cuticular excretions and molting get rid of themexcretions and molting get rid of them

Most problems lie with prevention and/or Most problems lie with prevention and/or treatment of virusestreatment of viruses

Shrimp ImmunologyShrimp Immunology As mentioned, shrimp have both a cellular As mentioned, shrimp have both a cellular

and humoral response to viruses:and humoral response to viruses:– Certain proteins respond to Certain proteins respond to -glucan -glucan

(component of bacterial cell wall)(component of bacterial cell wall)– Hemocytes attack bacteria, release compounds Hemocytes attack bacteria, release compounds

causing browning reaction in the HPcausing browning reaction in the HP But… no antibodies generated!But… no antibodies generated! No No defensedefense against viruses has to date against viruses has to date

been described in any detail...???been described in any detail...??? ConclusionConclusion: there must be some defense : there must be some defense

that has been overlooked!that has been overlooked!

Shrimp ImmunologyShrimp Immunology There is also little histological response to There is also little histological response to

viruses: blood cells don’t go to locationviruses: blood cells don’t go to location Viral infections are persistent, remain Viral infections are persistent, remain

evident for life of shrimpevident for life of shrimp Despite having no set specific response to Despite having no set specific response to

specific viral pathogens, shrimp appear to specific viral pathogens, shrimp appear to have a have a high tolerance to themhave a have a high tolerance to them

Case in point: historical information on Case in point: historical information on viral epizootics in Southeast Asiaviral epizootics in Southeast Asia

What’s Going On?What’s Going On? Our current management practice is to Our current management practice is to

look for look for SPFSPF, , high-healthhigh-health animals for animals for stocking pondsstocking ponds

Most PL’s derived from new sources, not Most PL’s derived from new sources, not from survivorsfrom survivors

The history of each batch is important The history of each batch is important to know!to know!

ImplicationImplication: perhaps SPF animals are : perhaps SPF animals are not appropriate!not appropriate!

““Normal” ShrimpNormal” Shrimp If you sample a normal shrimp pond in SE Asia, If you sample a normal shrimp pond in SE Asia,

88% of shrimp are infected with a virus88% of shrimp are infected with a virus 53% have been infected with two to three viruses53% have been infected with two to three viruses Survival now (after multiple years in population) Survival now (after multiple years in population)

has returned to a more or less normal levelhas returned to a more or less normal level Does this indicate Does this indicate resistanceresistance or or tolerancetolerance?? ResistanceResistance = no sign of pathogen in individual; = no sign of pathogen in individual;

however, virus can be detected in tissueshowever, virus can be detected in tissues ConclusionConclusion: something different from resistance: something different from resistance

Theory of Viral Theory of Viral AccomodationAccomodation

Shrimp viral response is an active processShrimp viral response is an active process Involves binding of viron to receptor site Involves binding of viron to receptor site

that triggers some kind of “memory”that triggers some kind of “memory” Binding is not related to infection receptorBinding is not related to infection receptor Memory causes reduced Memory causes reduced apoptosisapoptosis Subsequent binding turns off ability of virus Subsequent binding turns off ability of virus

to induce death in hostto induce death in host Death is prevented, but not infectionDeath is prevented, but not infection Viral replication can take place, but no Viral replication can take place, but no

deathdeathApoptosis: the process of cell death which occurs naturally as part of the normal development, maintenance and renewal of tissues within an organism. Occurs when a virus infects a cell.

Dr. Tim Fleigel

Viral Infection is a Phased Viral Infection is a Phased ProcessProcess

InitialInitial: brief and evolutionary with acute : brief and evolutionary with acute mortality via apoptosis, leads to mortality via apoptosis, leads to intermediate phaseintermediate phase

IntermediateIntermediate: virus and host live : virus and host live together, but without mortality; better together, but without mortality; better host survivors replicate so population is host survivors replicate so population is positively selected for against viruspositively selected for against virus

FinalFinal: hard to find virus, mutual : hard to find virus, mutual existence governed by genetic factorsexistence governed by genetic factors

AccomodationAccomodation Higher virulence is naturally Higher virulence is naturally

selected againstselected against No resistance to infection = No resistance to infection =

reduced or low virulencereduced or low virulence PointPoint: no pressure on virus to : no pressure on virus to

become virulentbecome virulent PointPoint: may increase competition : may increase competition

for new viruses to enter host!for new viruses to enter host!

What to Do???What to Do??? Use survivors as a source of broodstockUse survivors as a source of broodstock Expose progeny to virus or Expose progeny to virus or tolerenetolerene to to

develop tolerance (avirulent virus)develop tolerance (avirulent virus) When? Possibly at Zoea 3 or earlierWhen? Possibly at Zoea 3 or earlier How? Tolerene developed specifically for How? Tolerene developed specifically for

each viruseach virus ImplicationsImplications: for larval rearing, it means : for larval rearing, it means

introduction of a introduction of a tolerenetolerene in proper form in proper form

Virology Summary: Virology Summary: Shrimp vs. FishShrimp vs. Fish

No clear response to No clear response to virusesviruses

Survivors remain Survivors remain infectedinfected

Pathogen persistsPathogen persists Survivors infectious Survivors infectious

to othersto others Tolerance is a normal Tolerance is a normal

situationsituation No antibodiesNo antibodies Multiple active Multiple active

infections are normalinfections are normal

Specific response to Specific response to virusesviruses

Survivors often don’t Survivors often don’t remain infectedremain infected

Pathogen removed Pathogen removed from bodyfrom body

May or may not be May or may not be infectious to othersinfectious to others

Tolerance not normalTolerance not normal Antibodies presentAntibodies present Usually only one Usually only one

virus at a timevirus at a timeSHRIMP FISH

Immune Response of Aquatic Organisms

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