The Immune System AP Biology Unit 6 Types of Immunity Innate Immunity = non-specific protection...
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Transcript of The Immune System AP Biology Unit 6 Types of Immunity Innate Immunity = non-specific protection...
The Immune SystemThe Immune System
AP BiologyUnit 6
Types of Immunity
• Innate Immunity = non-specific protection against many different microbes
• Acquired Immunity = specific protection against microbes
Nonspecific Defenses
• Target a wide range of pathogens (non-specific foreign body) – Examples include: skin, mucous membranes,
inflammatory response, phagocytic cells
Nonspecific Defenses: Lymphatic System
• “filters” interstitial fluid and blood continually
• immune system cells in the lymph (in lymph nodes) take care of foreign particles and microbes
Phagocytosis
• phagocytes are white blood cells (leukocytes) that ingest microbes
• neutrophils and macrophages are the most common
Antimicrobial Proteins
• Complement System– Series of 30 proteins that are usually present in
the blood (inactive)– Activated when microbes are present (by
molecules on the surface of microbes)– Creates a cascade of reactions results in the
microbe cells bursting– May also trigger inflammatory response (by
attracting phagocytes)
Antimicrobial Proteins: Interferons
• Secreted by cells infected by viruses
• Causes nearby cells to inhibit viral reproduction/replication
• Not virus-specific
• Because of these, you aren’t as likely to get 2 viral diseases at the same time
Inflammatory Response
• A non-specific way to protect tissues from possible infection by destroying invading bacteria
Signs of Inflammation
• Redness– Due to the dilation of blood vessels
• Swelling– Due to extra fluid in the area
• Heat– Due to dilation of blood vessels (increased
blood flow)
• Pain– Extra fluid presses on nerves
Inflammatory Response
• Chemokines are small proteins that guide macrophages and signal them to increase lysosome contents
Natural Killer Cells
• Recognize virus-infected cells and cancer cells
• They directly release lethal chemicals, leading to apoptosis
Image taken without permission from http://www.news.utoronto.ca/images3/killercells.jpg
Specific Defenses
• Antigen = foreign body recognized by acquired immune system
• Examples of antigens include viruses and bacterial toxins
• Antibodies in the immune system bind antigens
Half way through day 1 lecture…
Specific Defenses
• B cells and T cells are lymphocytes with receptors that each recognize a specific antigen. – Ex. Specific B and T cells recognize the cold
virus, but not the chicken pox virus.
• After recognizing the specific antigen, certain cells are activated to eliminate the antigen or infected cells
B and T Cell Receptors
• The receptors on B and T cells and antibodies are formed from the random rearrangement of gene segments– Like different
combinations of the letters in the alphabet make different words
Humoral Immune Response
• Involves the actions of antibodies
• Antibodies– Proteins also known as Immunoglobulins – Tremendous Diversity—there are thought to be
millions (1015) of different specific antibodies
B cells
• Each B cell has a different antigen receptor on it
• Mature in the bone marrow
• Differentiate to become Memory cells or Plasma (Antibody-Secreting) cells after binding to the appropriate antigen
B cells
• “Anti-self” cells are destroyed before fully differentiating (Clonal Selection) – This has to occur since the antigen receptors are
formed from RANDOM gene rearrangements could accidentally produce a receptor that recognizes a body cell/molecule
– Autoimmune diseases result when clonal selection fails
Steps of the Humoral Response
1. Macrophage presents antigen on Class II MHC and binds to Helper T Cell
– MHC proteins are on the surface of cells and bind antigens
Steps of the Humoral Response
2. Helper T Cell secretes cytokines
Cytokines activate other Helper T Cells
Steps of the Humoral Response3. B cell with specific antibody binds to antigen (at the
same time Helper T cells are being activated)
4. Cytokines activate B cell to divide and differentiate into: Plasma Cells and Memory B cells
5. Antibodies combine with antigens all over body and help to facilitate phagocytosis
Plasma Cells
• Secrete loose antibodies into the bloodstream– Like antibody factories
• Plasma cells have a lot of ribosomes and Rough ER– WHY?– Antibodies are proteins these are the
organelles needed for protein synthesis
Image taken without permission from http://bcs.whfreeman.com/thelifewire/default.asp?s=&n=&i=&v=&o=&ns=0&uid=0&rau=0
Actions of Loose Antibodies
• Surround virus/bacteria prevent it from binding to and infecting cells
• Antibodies can bring together multiple bacteria or antigens, making them much larger and hence more noticeable for destruction by macrophages or phagocytes – clumps them together
End of Day 1 Lecture
Cell-Mediated Response
• Involves the action of Cytotoxic T Cells
• Eliminates infected cells, cancer cells, and transplanted cells
T cells
• Arise from lymphocytes maturing in the thymus gland
• Differentiate to become Cytotoxic T Cell or Helper T Cell – Helper T cells also participate in Humoral
Response
• Differentiate to become Memory cells or Effector cells– Effector cells will act immediately, memory
cells act later if the microbe returns
T Cells
• The receptors on each T cell are specific to an antigen
• T cell receptors can also recognize antigen fragments
Steps of the Cell Mediated Response
1. Infected cell presents antigen on Class I MHC
2. Cytotoxic T Cell recognizes antigen and binds to it
Steps of the Cell Mediated Response
3. Cytotoxic T Cell reproduces (clones itself)
4. Cytotoxic T Cells bind to antigen bound to infected cells and release perforin to lyse infected cells
Primary versus Secondary Response
• Primary Response = initial immune response to antigen
• Secondary Response = immune response when exposed the same antigen a second time (carried out by Memory cells)
Primary vs. Secondary Response
• The secondary response is much faster than the primary response– More antibody & T cell production in a shorter
amount of time
Primary response
Secondary Response
Helper T cells
• Participate in both the Humoral and Cell-Mediated Immune Responses
• the HIV virus attacks Helper T cells
Immunizations
• Active immunity = immunity due to exposure to an antigen (produces memory cells)
• Immunizations (vaccinations) allow an individual to develop active immunity to an antigen without actually getting “sick” during initial exposure
• Vaccines are usually made up of weakened viruses or microbes
Immune Responses to Donor Tissue• There are 3 kinds of antigens associated
with blood: A, B, and Rh – Antibodies are produced that react to the wrong
blood type (Anti A and Anti B)– This causes agglutination (clumping of RBCs)
and lysis (bursting) of RBCs which can lead to serious conditions
Blood Donors and Recipients
• What blood type is the Universal donor? – Type O does not have any surface antigens
(A or B) so the donor’s body will not attack it
• What is the blood type of the Universal recipient? – Type AB no anti A or B, so it won’t attack
any of the other blood cells
Rh factor
• The Rh factor is another surface protein that is found on the surface of red blood cells
• An individual either has the Rh factor on RBC (+) or doesn’t (-) – genetically determined
• Individuals who are Rh- will produce antibodies that attack Rh+ cells– This is particularly dangerous if a mother is Rh-
and her fetus is Rh+ (she produces antibodies against Rh)
Tissue Donors
• In tissues, the body looks at MHC molecules to identify self from non-self.
• What is the best host of tissue you might need for a transplant? – Yourself or someone very closely related to
you (identical twin would be ideal)
Allergies
• When the immune system “overreacts” or becomes hypersensitive to certain antigens
• Most allergies involve the actions of IgE antibodies – This causes mast cells to release histamine
Allergies
• Histamine triggers inflammatory responses leads to allergy symptoms such as runny nose, tearing eyes, etc.
• Many allergy medicines are antihistamines to block the receptors for histamine
Autoimmune Disorders• When the immune system fails to recognize
a body cell as a self cell and attacks it – Could be due to a failure in clonal selection
• Examples include: – Lupus (attacks a variety of body cells) – Rheumatoid Arthritis (attacks cartilage and
joints between bones) – Type I Diabetes (attacks beta cells in pancreas
that produce insulin) – Multiple Sclerosis (attacks myelin sheaths on
nerves)
HIV: the Basics
• The Human Immunodeficiency Virus attacks Helper T Cells
• HIV progresses to AIDS when white blood cell counts reach a certain low
• HIV is a retrovirus (RNA is the nucleic acid inside)
HIV: the Basics
• Mutations to the HIV surface antigen occur each time the virus replicates, which is why finding a cure is difficult.
• Drugs can help slow HIV reproduction but some drug resistant strains have now been generated from mutations during viral replication
ELISA
• ELISA = Enzyme Linked Immunosorbent Assay
• This is a test that detects the presence of specific antibodies in the blood to determine if an individual has a certain condition
• The same principles are used in home pregnancy tests
ELISA• The ELISA plate is coated
with antigens specific to the antigen being tested for (ex. Chicken pox)
• Blood is added that may contain the antibodies (present only if the person has the disorder)– Only the specific antibody
will bind to the antigen on the plate
antigens
ELISA
• Unbound antibodies are washed away
• A secondary antibody (anti antibody) is added that will bind to the antibody already bound to the antigen
• The secondary antibody has an enzyme attached to it
After washing
Secondary Antibody
ELISA• After washing away unbound
secondary antibody, a substrate is added
• If there is secondary antibody in the well (bound to the antibody), there will also be enzyme present to break apart rhe substrate
• Breaking apart the substrate causes a color change antibody present
ELISA and Pregnancy tests
• Home Pregnancy tests use the same principles as home pregnancy tests.