Wednesday April 14,1999
Announcements:

Lecture notes:

An antibody is a type of receptor with a specific binding site for 1 type of antigen. ANTIBODIES ARE PROTEINS.

It is produced by B-cells and by decedents of B-cells called plasma cells. (Effector Cells)

Each B-cell produces just one type of antibody which it displays on its cell membrane at maturity.

B-cells that haven't come in contact with antigen are called virgin B-cells.

Antibody molecules are shaped like a Y. The amino acid sequence has constant regions at the base and fork of the Y, and variable regions at the tips of the arms of the Y.

This is what allows for the millions of different antibodies we can produce.

**BE CAREFUL: ANTIBODY ABD ANTIGEN - DON'T MIX THEM UP**

There are five classes of antibodies, each with slightly different shapes and each with different functions.

Collectively, they are called the Immunoglobulins. They form a large part of the proteins that circulate in the blood and lymph.

IgM and IgG: Activate macrophages and the complement system, as well as supply antibodies for most foreign invaders.

IgE: Stimulate mast cells to release histamine. (Also involved in protection against infection by worms.)

IgA: present in saliva, tears, lungs and intestines.

3 main actors: B-cells, helper T-cells and macrophages.

1. Invasion (for example a bacteria)
2. B-cells Macrophages
   Virgin B-cell binds to antigen Macrophage engulfs bacterial cell and
   on bacteria and "processes" it. helps with inflammation.
3. Antigen is displayed near MHC Macrophage "processes" and displays
   marker on B-cell. antigen.
4. Enter the Helper T-cell specific for this antigen.
5. The Helper T-cell binds to the antigen-MHC Complex on the surfaces of both the B-cell and the macrophage.
6. This binding plus secretions by macrophages and helper T-cells cause the B-cell to become activated and differentiate into plasma cells - weapons factories.
7. Some B-cell progeny become memory cells.
8. Plasma cells spew out 2,00 molecules of antibody/second.
9. They find and bind to antigen.
10. "Marked" bacteria are destroyed by macrophages and complement.

T-cells mature in the thymus.

Some mature into future Killer T-cells by displaying antigen receptors on their surfaces. (they look like antibodies)

They lock onto body cells with MHC proteins with an antigen displayed on it.

The killer T-cell excretes "perforin" that perforates the infected cell and kills it. Killer T-cells create memory cells once activated.

**The cell mediated response is implicated in transplant rejection**

Remember: both B-cells and killer T-cells create memory cell once activated.

Primary Immune Response: the first exposure to an antigen. It takes 5 or 6 days to make antibody. By this time you can
be very ill with a disease.

Secondary Immune Response: Subsequent invasions take only 2-3 days to mount a response and the response is of a
greater magnitude and duration that the response to the antigen upon first encounter.

**This is the basis for immunization**

*For many diseases we acquire a permanent immunity after we get that disease. (mumps)

*For some we never gain immunity. (Syphilis, gonorrhea)

we can also gain immunity without getting a disease.

Passive Immunity confers some immunity when antibodies form someone else are introduced into a person needing immunity.

1. Babies get antibodies from their mothers while in the womb. They are present at birth and are slowly cleared from the circulation or are degraded (die)
2. Babies who breast feed get antibodies form colostrum and breast milk.
3. People already exposed to serious diseases such as hepatitis, tetanus, diphtheria, botulism, etc. can be given an injection of "immune globulin" which contains antibodies extracted from human serum or made in the lab.

Passive Immunity provides some protection against the disease.

This protection is temporary.

Some people react badly to the injection of foreign proteins.