Antigen-Antibody Reactions

To bridge the gap between basic immunology and antibody detection methods (Module 3), we will now briefly review the nature of antigen-antibody reactions. The antigen-antibody reactions that are used most in blood banking are known as hemagglutination, i.e., they cause the agglutination of red cells. These reactions take part in two stages, sensitization and agglutination. In the first stage (sensitization), the antibody binds to the red cell or sensitizes it. In the second stage, the sensitized red cells agglutinate. Although sensitization occurs first, it and agglutination ultimately overlap to some extent. Below is a simplified discussion of these reactions and the factors that affect them.

• First Stage (Sensitization)

• Second Stage (Agglutination)

Enrichment activity #3

E-mail responses to Questions #1-3 to Pat.

Review the diagrams and materials at these antibody-related sites:

• figure 5-15

• figure 5-16

• antibodies

1. Of the body's total immunoglobulins, which percentage is composed of IgG, of IgA, and of IgM?

2. Visit monoclonal antibodies and hybridoma graphic.

   (a) What is a "hybridoma"?

   (b) Describe how monoclonal antibodies are produced.

3. Although initially used to treat immunodeficiency, intravenous immunoglobulin (IVIG) has also been used as prophylaxis and therapy in many other diseases. Its use continues to grow rapidly. See, for example, this NIH statement on IVIG.

   (a) List eight diseases for which IVIG has been used with some success.

   (b) In conditions such as immune thrombocytopenia purpura (ITP), describe proposed mechanisms by which IVIG is believed to act.

4. At the NIH site, one of the hypothesized mechanisms by which IVIG may act involves anti-idiotype antibodies. E-mail a comment or question about anti-idiotype antibodies to the class mailing list.

Antigen-Antibody Reactions