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Memory cells

Effector T-cytotoxic cells destroy cells that presented antigen via MHC class I molecules; also produce cytokines that allow neighboring cells to become more vigilant against intracellular pathogen.

Figure 16.21 Summary of the Adaptive Immune Response

Generation of Diversity

The mechanisms lymphocytes use to produce a nearly infinite assortment of antibodies and antigen-specific receptors were first revealed in studies using B cells. Because the processes are markedly similar to those employed by T cells, we will use them as a general model to describe the generation of diversity with respect to specificity for antigen.

Each B cell responds to only one epitope, yet it is estimated that the population of B cells within the body can respond to more than 100 million different epitopes. Based on the information presented in chapter 7, it might seem logical to assume that humans have over 100 million different antibody genes, each encoding specificity for a single epitope. The human genome, however, has only 3 billion nucleotides and codes for only about 30,000 genes.

The question of how such tremendous diversity in antibodies could be generated perplexed immunologists until Dr. Susumu Tonegawa solved the mystery. For this work, he was awarded a Nobel Prize in 1987. Diversity in antibodies involves a combination of gene rearrangement, imprecise joining of gene fragments, and the association of light chains and heavy chains coded for by the rearranged genes.

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