MICR130 Immunology part 2 (applications + disorders) - Quiz 12/13

Tests, adaptive immunity

ELISA

Enzyme Linked Immunosorbent Assay

Introduces an enzyme’s substrate (eg. detecting presence of enzyme urease / production of ammonia to test for H. pylori activity)

Anti-human antibody linked to enzyme (eg urease) introduced. Add substrate (urea) and pH indicator. Reaction will take place only if human anti-virus-antibody is present

eg. take-home pregnancy tests

Direct ELISA: detects antigen, antibody is added + patient sample with antigen added

Indirect ELISA: detects antibodies, antigen is in well + patient serum added

Fluorescent Microscopy (Fluorescent-Antibody Techniques / FA)

Identifying microbes / antibodies with fluorescent dye FTIC / TRITC

Antigens react with antibody and glow under microscope

Fluorescence Activated Cell Sorter (Fluorescent-Antibody Techniques / FA)

Fluorescent cytometry

Instrument with laser counts and separates fluorescent stained cells

eg. Can be used to count number of CD4 (helper T cells) and CD8 cells in a sample to test for the progression of AIDS for less CD4 cells

Agglutination

Detects particulate antigens (particles/cells carrying antigenic molecules) or soluble antigens adhering to particles

Antigens will link together to form visible aggregates (clumped together masses)

Direct vs Indirect agglutination

Direct: Detects antibodies against regularly large cellular antigens and clumping of these cells naturally eg. red blood cells, bacteria, fungi

Indirect / Latex agglutination: Antigen (or antibody) is attached to larger particles to improve visualization, and observing the aggregation of those, such as latex beads.

Common testing for strep

Precipitation

Detects soluble antigens with IgG or IgM antibody

Antigens and antibodies bind, creating antigen-antibody complexes that form large, insoluble lattices

Area of equivalence

Precipitation tests require an optimal ratio of antigen to antibody

Antigen/antibody placed adjacent to each other, and a cloudy line of precipitation forms in the area with the optimal ratio

Clonal Selection Hypothesis

1. Stem cells differentiate into B cells and are already present in body since birth

2. B cell encounters an antigen without T cells, producing a weak immune response (IgM / first response)

3. Some B cells proliferate to become memory cells, some proliferate into plasma cells (type of specialized B cell proliferates when it encounters an antigen / is selected)

4. B cells that proliferate into memory cells can be stimulated to become plasma cells that produce antibodies against the antigen it encountered. Same cell might class switch (produce a different antibody than IgM— eg. IgG or IgE)

5. Plasma cells secrete antibodies into circulation

First vs Secondary Response

First response:

• IgM

• Naive cells

• Takes place first, weaker, less antibody

Secondary response:

• Intensified immune response after first due to memory cells

• Less IgM, class switching, more antibody made

• (vaccination/artificially acquired immunity can be explained by this response)

HCG (hormone that produces placenta) latex inhibition agglutination test

1. Add urine + antibody reagent, allowing antigen + antibodies to bind

2. Add HCG latex beads

3. If HCG is present, will already be bound to the antibodies and thus antibodies will not bind to the latex particles

Inhibition (no clumping): positive / pregnant

Clumping: negative

Reagent antibodies

Specific, sensitive reagents made in animals that bind to specific molecules

Type I hypersensitivity

What is it/what is involved, examples?

Anaphylactic

Fast acting <30 min

Reaction from IgE on basophils/mast cells binding with antigens

• Antigen bridges gap between two antibodies, causing degradation (cell releases its granules + contents, including histamine)

Eg. common allergic reactions (mucousal secretions, itchy eyes), shock in systemic rx

Type II hypersensitivity

What is it/what is involved, examples?

Cytotoxic

IgG/IgM reacts with antigen to activate complement, then lyses cells

Antigens located on cell or tissue surfaces

Eg. blood transfusion reactions, erythroblastis fetalis/HDNB (hemolytic disease of newborn)

Type III hypersensitivity

What is it/what is involved, examples?

Immune complex reactions

IgG/IgM reacts with soluble antigens in serum to form an antibody-antigen complex that is deposited in tissues. Complement is activated, causing inflammatory damage

• Complex circulates blood then becomes trapped in basement membrane endothelial cells. Immune complex activates complement and endothelial cells/membrane is damaged by enzymes from neutrophils

Eg. serum sickness, autoimmune conditions such as Rheumatoid arthritis, Post-Strep glomerulonephritis, Grave’s disease, Lupus, Arthus reaction (side effect of toxoid vaccines)

Type IV hypersensitivity

What is it/what is involved, examples?

Delayed cell-mediated reaction

Delayed (24-28 hours) cell-mediated (involves CD4 T cells)

• Macrophage antigen presentation → T cells become memory cells then proliferate (no dermatitis during sensitization)

• Dermatitis occurs upon secondary contact as memory cells release cytokines + cause inflammation

Eg. contact dermatitis (poison ivy, mango rash), PPD (purified protein derivative of tuberculosis) test

Erythroblastis fetalis and how to treat it?

Rh- mother carries Rh+ fetus then becomes immunized during her first pregnancy

During 2nd pregnancy with Rh+ fetus, mother produces antibodies that damage fetal RBCs causing jaundice and anemia

Preventable with RhoGAM: anti-Rh antibodies (blocking antibodies) to combine with the fetal Rh+ instead of her immune system to prevent mother from being immunized during 1st pregnancy

Fc region of IgE

IgE binds to mast cells via the Fc region

Mast cells have Fc-IgE receptors

Hyposensitization therapy

Desensitization therapy

Used to treat type I hypersensitivity

Patient is repeatedly immunized with small doses of allergen to try to force the immune system to synthesize IgG instead of IgE

If successful, IgG binds to allergen before IgE, thus blocking the allergic response

Blocking antibody

An antibody that binds to a specific target to prevent other molecules from binding to it

eg. IgG in hyposensitization therapy, RhoGAM

Natural antibodies

Antibodies that exist in our plasma without prior immunization

In ABO group system, individuals possess antibodies to antigens they don’t possess

Immune complexes

Soluble, circulating antigen-antibody aggregate that can fix to complement

Form under certain ratios of antigen and antibody

Type III hypersensitivities (Grave’s disease, lupus, rheumatoid arthritis, serum sickness)