ANTIBODIES def - protein molecules that combine specifically with antigens. Proteins with antibody activity are known as immunoglobins.

A. Structure - four polypeptide chains Fab Fc- fragment crystalline light chain heavy chain S S SS SS Fragment antigen binding DISULFIDE BRIDGES

B. Classes - IgG, IgA, IgM, IgD, IgE

1. IgG most versatile neutralizes toxins activates complement opsonization - “candy coats” only class to pass the placental barrier longest half life important to secondary response

2. IgM can form a ringed pentamer only class synthesized in the fetus reacts to ABO blood system excellent at complement fixation excellent at agglutination important in the primary response

3. IgA antiviral present in tears, saliva, colostrum, sweat, mucus

4. IgD found on B cells play a role in B cell differentiation (formation of plasma cells, which secrete antibody and memory cells which are important to secondary response)

5. IgE protects against parasitic worms binds to mast cells and basophils play a role in hypersensitivity

C. GENETIC BASIS FOR ANTIBODY FORMATION 1. There are an estimated 1,000,000 to 100,000,000 different Ab in an individual 2. Antibodies are pieced together from distinct regions of DNA 3. Antibody genes can move and rearrange themselves within the genome of a differentiating cell 4. See pages AND of the notes for more detail