•Production of new lymphocytes (lymphopoiesis): in central lymphoid tissues
• B cells: bone marrow; fetus (fetal liver, yolk sac)
• T cells: precursor cells in bone marrow and then migrate to thymus
•
•Ag specificity of an individual lymphocyte is determined early in its differentiation by gene rearrangement. The early stages of B and T cell development proceed along broadly similar lines.
•
•Specificity and affinity of the receptors determine the fate of the immature lymphocytes
•
• -Positive selection: interact weakly with self Ag. Receive signals to survive. Eg. α:β T cells recognize peptide bound to MHC
• -Negative selection: lymphocytes whose receptors bind strongly or not at all to self antigen and receive signals to die (immunological tolerance).
•
Lymphocyte Development and Survival—Part 1