Specific Defenses Of The Host (Adaptive Immunity)

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Antigen or immunogen

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Is a chemical substance that causes the body to produce specific antibodies or sensitized T-cells.

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Antiserum

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A blood derived fluid containing antibodies.

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serology

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The branch of immunology that studies blood serum and antigen-antibody rxns in vitro (test tube, Petri dish or inside a living organism).

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antibody

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A protein produced by B-cells in response to an antigen, and capable of combining specifically with its specific antibody. An antibody has at least two identical antigen-binding sites.

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Gamma globulin

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The serum fraction containing immunoglobulins (antibodies); also called gamma globulin.

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immunoglobulins (Ig)

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A protein (antibody) formed in response to an antigen and can react with that antigen.

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Describe an IgG antibody molecule.

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The igG antibody molecule is shaped like a Y. It contains two heavy chains and two light chains. The two branches of the Y each contain one light chain and one part of each heavy chain. The stem of the Y is composed of the remaining parts of the two heavy chains

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What do the Fab and the Fc portions of the antibody determine?

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-The Fab (the top arms region of the Y) fragment antigen binding determines specificity.

-The Fc (stem region of the Y) fragment determines antigen class.

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List the 5 classes of antibody & give the major characteristics of each.

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-IgG- monomer; are most abundant in serum, it CROSSES the placenta, recognizes Rh antigens.

-IgM- have 5 monomers(pentamer- 10 binding sites), does NOT cross placenta, recognizes ABO antigens.

-Serum IgA- 2 dimers; secretions/body fluids (mucus, tears, saliva, and colostrum), protect mucosal surfaces.

-IgD- monomer; antibodies are antigen receptors on B-cells; no known function.

-IgE- monomer; antibodies bind to mast cells and basophils and are involved in allergic rxns.

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B cells

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a type of lymphocyte; differentiates into antibody-secreting plasma cells and memory cells

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macrophages

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a phagocytic cell; a mature monocyte

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helper T cells

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a specialized T cell that often interacts with an antigen befor B cells interact with the antigen

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plasma cells

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a cell that an activated B cell differentiates into; plasma cells manufacture specific antibodies

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memory cells

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a long-lived B or T cell responsible for the memory, or secondary response.

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Four types of adaptive immunity

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1) Naturally acquired active immunity: Exposure to foreign antigen (pathogen)

2) Naturally acquired passive immunity: Breastfeeding IgA (colostrum) and cross the placenta (IgG), mother to baby.

3) Artificially acquired active immunity: Vaccines (actual antigen)

4) Artificially acquired passive immunity: Antibodies injected (i.e., Rhogam, anti-venom, antiserum)

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Antibody-Mediated (humerol) immunity:

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Involves B-cells (which have individual (single) specificity (DNA rearrangement). Each B-cell is geared for different antigens (specificity), i.e., (trillion) specificity. At random, DNA is rearranged and that is how it is possible for the trillion-plus specificity.

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Macrophages (APC) Antigen-presenting cell.

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Foreign antigen (on the APC) binds to a receptor on a helper T-cell, and activates it. When macrophages phagocytize they put (present) fragment of pieces on the outer edge of the cell wall.

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Helper T-Cells:

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The helper T-cell, once activated, sends a message to activate the B-cells; Active the immune response

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B-Cells:

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Once the B-cell is activated by the Helper T-cell, it either multiplies (proliferates) and becomes a plasma cell, or in a few instances, will become a memory B-cell.

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Plasma Cells:

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Plasma cell secretes antibodies (against the original bacteria) outside the cell wall (into the blood), which is then eaten by the macrophage.

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Memory Cells:

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Remember that pathogen and next time will start the immune response faster so the pathogen doesn’t become a disease.

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What are the results of antigen-antibody binding: (or functions)

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1) Agglutination: Clump them together (viruses; bacteria)

2) Opsinization: Enhancement
of phagocytosis by stimulation

3) Antibodies activate complement (stimulates inflammation and MAC)

4) Neutralization (of viruses and toxins)

5) Antibody-dependent cell mediated cytotoxicity – stimulated by antibodies (eosinophils – tells them what to attack)

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Primary Immune Response:

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The first time your body is exposed to a virus/ pathogen. It takes a while for the immune system to catch up with the pathogen. (During the time that the immune system is being activated, you have the disease).

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Secondary Immune Response:

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Remembers the pathogen, and the immune system will start faster so that the pathogen does not become a disease; responds faster, stronger, and lasts longer.

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CELL MEDIATED (CELLULAR) IMMUNITY:

What three types of cells are killed by cytotoxic T-cells?

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1. Virus infected cells – have different proteins on their surface.
2. Tumor cells – also have different proteins on their surface
3. Transplanted cells – Tissue rejection

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Cytokines:

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A small protein released from human cells in response to bacterial infection; directly or indirectly may produce fever, pain, or T-cell proliferation.

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Antigen-presenting cells

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(APC) – Macrophages and dendritic cells:

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Cytotoxic T-cells (Killer T-Cells):

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(Killer T-Cells): Also have specificity; get activated by Helper T-cells

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Suppressor T-cells:

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Have the opposite effects of Helper T-cells; suppress the immune response

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Natural killer cells:

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Not specific (no specificity for antigens); Similar to cytotoxic T-cells

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What cells are infected by HIV?

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CD4 receptors

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Why is HIV infection so effective at suppressing the immune response?

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HIV – attacks the cells that are important in the immune system. Immunosuppressive meds suppress the cytotoxic T-cells

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Explain why vaccinations work?

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Stimulate a primary immune response so if you are exposed to the pathogen again, the secondary immune response will begin. (Vaccines are the primary response).

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Inactivated (Non-living/killed) whole-agent vaccines:

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Salk polio vaccine: First one in the 50’s
Influenza vaccine (injected): Specific to the strain(s) (H&N spikes)
Trivalent (against three different strains)

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Attenuated (Weakened) whole agent vaccines: Can still infect

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Sabin polio vaccine: (oral) The virus has to be active –
Enters thru the lining of the intestines. Multiplies slowly – faster immune response because it is alive – makes more antibodies.
Influenza vaccines (nasal sprays)

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Subunit Vaccines (not the whole agent/virus; just pieces of the cell wall)

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Acellular pertussis vaccine: Whooping cough – bacteria causes this – the toxin (safety issue)
Hepatitis B vaccine: Use a protein coat or spike – no nucleic acid – won’t reproduce (recombinant)

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Conjugated vaccines (attach it to another protein that will stimulate an immune response)

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Haemophilus influenzae b (Hib) vaccine (surface is a polysaccharide)

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Toxoids (modified toxins, no longer toxic)

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Diphtheria vaccine retain enough of the strain, so that antibody will be recognized.

Tetanus vaccine

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Combined multiple vaccines (because there is more than one – easier)

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DPT: diphtheria, pertussis and tetanus

MMR: measles, mumps and rubella (attenuated)

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Explain the use of the TB (PPD) skin test and BCG vaccine:

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To see whether you are going to have a secondary response – put in a protein under the skin – if you have been exposed, you will have a reaction (rash, bump).

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SEROLOGY:

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(Serum/antiserum (serum with antibodies against some kind of antigen)

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What are the benefits of using antibodies for diagnostic immunology (serology)?

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1. Use antibodies to detect antigens (Ag)

2. Use antigens to detect antibodies (ABS)

These tests are specific and sensitive. Easy to use (i.e., home pregnancy test – enzyme is used – resultant color change)
-The human chorionic gonadotropin (hCG) test is done to measure the amount of the hormone hCG in blood or urine to see whether a woman is pregnant.

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What techniques are used to detect antibody-antigen binding?

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ELISA: (Enzyme-linked immunosorbent assay): A group of serological tests that use enzyme reactions as indicators.

RIA (radio immunosorbant assay): Uses radioisotopes/Geiger counter; extremely sensitive
Immunofluorescent: resultant neon color

Precipitin ring test: Add the possible antibodies – agglutinate (clump together – see a powder on the bottom). Done in a capillary tube.