Post on 30-Dec-2015
Introduction to ImmunityImmunity is a physiological reaction of the body to
factors it considers threatening and foreign to it
Immune system can distinguish ‘self’ from ‘non-self’
A factor which evokes the immune response is referred to as an Antigen (or immunogen)
Antigens may be isolated molecules or may be molecules at the surface of an invading cell
Antigens are usually exogenous, but may be endogenous (i.e. part of the auto immune reaction)
Non Specific or Specific Immunity?
Non-specific = Innate = Inherited defence mechanisms
Specific = Acquired = Prior exposure
Non-specific Immunity Eyes, Mouth, NoseLungs, Skin, StomachReproductive SystemLarge intestine, Urinary Tract
Non-Specific Immunity
Eyes e.g. Lysozyme in tear fluid, flushing action
Mouth e.g. Lysozyme in saliva, flushing action
Nose e.g. sneezing, nose hairs
Non-Specific ImmunityLungs
e.g. coughing, muco-ciliary clearance
Skine.g. waterproof skin/physical barrier, sebum and acid pH
Non-Specific ImmunityStomach
e.g. HCl in gastric juice
Reproductive Systeme.g. competition from harmless bacteria in vagina, acid pH of vagina, antibacterial proteins in semen
Non-Specific ImmunityLarge intestine
e.g. competition from normal gut flora
Urinary Tracte.g. directional flow and flushing action of urine
Non Specific Responses: Phagocytosis and Inflammation
Phagocytosis
Phagocytes contain lysosomes with enzymes
Phagocytes adhere to, engulf and destroy (digest and recycle) micro-organisms
Phagocytosis
Neutrophils
Generated in bone marrow
Comprise 50-70% of total white cell count
Recognise and phagocytose unwanted or foreign materials, then die
Phagocytosis
Macrophages
Highly mobile cells that migrate through connective tissue
Widely distributed throughout body tissues
Role is to phagocytose large bacteria and dead body cells
Phagocytosis
Monocytes
Multiple roles in immune function:• Replenish resident macrophages • In response to inflammation signals, can move
quickly to sites of infection in the tissues and differentiate into macrophages
• Have large kidney shaped nucleus
[Recognition by phagocytes can be enhanced by the binding of antibodies to the bacteria]
PhagocytosisPhagocytes are attracted to the micro-organism by a
process known as Chemotaxis
Neutrophils and monocytes
are able to squeeze through
tiny gaps between adjacent
endothelial cells
(Diapedesis)
PhagocytosisWhat intracellular structures (necessary for digesting ingested
particles) are highlighted in the diagram ?
What happens to the bacterium?
InflammationMast cells release histamine
Histamine:
• Increases blood flow via vasodilatation
• Increases capillary permeability
Both processes result in more phagocytes to the area
Inflammation and Phagocytosis
Identify (on the diagram below):• The site of bacterial entry? • What has coated the bacterium? • Where have the antibodies come from? • Where is the phagocytic cell coming from? • What has activated the mast cells? • What chemical has the mast cell released? • What effects has this chemical had on the
capillary?• What is diapedesis?
Leucocytes
Leucocytes are attracted
to an area of inflammation
by Chemotaxis
In which order do the
leucocytes arrive at the
area of inflammation?
Additional points
• What are endotoxins?
• What are Cytokines (and some examples)?
• What is the Complement system?
• What are Interferons?
Specific or Acquired Immunity
The immune system also produces very specific responses
Antigens / Immunogens induce specific immune responses.
Antigens include: foreign proteins, bacteria, viruses, foreign cells
Lymphocytes
Specific immunity involves Lymphocytes
Lymphocytes are derived from stem cells in the bone marrow
Lymphocytes replace themselves by cell division
T Lymphocytes
Lymphocytes that seed
the thymus become
T lymphocytes
(the thymus atrophies
after puberty)
T lymphocytes do
not secrete antibodies
Types of T Lymphocytes
Helper T cells* Activation of other defence cells (e.g. production of antibodies by B cells)* Regulate the response of both T Killer cells
and B cells
Suppressor T Cells* Inhibit T and B cell activities* Affect the amount of antibodies secreted
and moderate immune response (‘switch off’ immunity)
Types of Lymphocytes
Killer T cells
* Destroy specific cells with antigens on their surface
* Must be in actual contact with their victim cells
* Defend against viral and fungal infections
T Lymphocytes provide cell mediated immunity
B Lymphocytes
B lymphocytes are processed in the bone marrow
B lymphocytes combat bacterial infections as well as viral infections by secreting antibodies into the blood and lymph.
Antibodies bind to Antigens
B lymphocytes provide humoral immunity (blood and lymph are body fluids or humors)
B Lymphocytes
B lymphocytes when stimulated produce:
a) Memory cells
b) Plasma cells
Antibodies
Antibody proteins are also known as immuno-globulins (or gamma-globulins)
[Immuno globulins may be found in, for example, colostrum]
Antibodies
lgG Main form of antibodies in circulation: production increased after immunization; secreted during secondary response
lgA Main antibody type in external secretions, such as saliva & mother’s milk
lgE Responsible for allergic symptoms in immediate hypersensitivity reactions
lgM Function as antigen receptors on lymphocyte surface prior to immunization; secreted during primary response
lgD Function as antigen receptors on lymphocyte surface prior to immunization; other functions unknown
Primary and Secondary Immune Response
On first exposure to a pathogen, the immune response is insufficient to combat the disease
There is a latent period in which there are insufficient amounts of specific antibodies
On second exposure to the same antigen antibody production is much more rapid
Application to practice• You might like to think about relevant cases from
practice (maintaining confidentiality, of course).
• You could also consider own history with regard to infections / vaccinations / problems with immunity (for example, when have you found yourself prone to infections?).
• For those with an interest in mental health, what is Agranulocytosis and what anti-psychotic drug has this listed as an adverse effect?
• What are the arguments for allowing children to be exposed to ‘childhood infections’?