Final answer:
The clonal diversity in B and T cells arises from gene mutation and recombination during their development. Clonal selection and expansion allow the immune system to selectively expand cells with receptors specific for invading pathogens, while central tolerance mechanisms remove or inactivate self-reactive B cells.
Step-by-step explanation:
Clonal Diversity in B and T Cells
The clonal diversity in B and T cells is a fundamental aspect of the adaptive immune system, allowing it to recognize a vast array of pathogens. This diversity is achieved by the mutation and recombination of genes that encode for antigen receptors in stem cell precursors of these cells. During the maturation process of B cells in the bone marrow, up to 100 trillion different clones of B cells are generated, each capable of producing a distinct antigen receptor. Similarly, T cells differentiate into clones with specific receptors.
Clonal Selection and Expansion
The concept of clonal selection and expansion applies to both B and T cells. For T cells, clones with receptors specific for antigens on a pathogen are selected and expanded. The interaction between the antigen-displaying MHC molecule and a complementary T-cell receptor (TCR) triggers the immune response and production of that specific T cell. For B cells, immature cells that recognize self-antigens undergo clonal deletion or clonal anergy, effectively establishing central tolerance. In contrast, B cells with receptors fitting foreign antigens expand to form antibody-secreting plasma cells and memory B cells.
Role of Cytokines
Additionally, once activated by linked recognition, T-helper cells (TH2) produce cytokines that prompt B cell proliferation into clonal daughter cells and differentiate into memory B cells for rapid response upon re-exposure to the antigen and plasma cells.