... these biochemical clusters which trigger the immune response. Immunological memory is the term used to describe how the adaptive immune system appears to remember all pathogens it has encountered previously, and changes behaviour as a consequence of earlier experience. It relates only to epitopes that have been encountered previously. Small lymphocytes are T and B cells found circulating in the blood and lymphatic system and stationary in the lymph nodes, spleen and other lymphoid organs. Each has receptor molecules on its surface with a unique structure and specificity that binds to just one epitope shape. B cells mature in the bone marrow. Contact with antigen › clonal expansion › differentiation into memory B cells or plasma cells. T cells mature in thymus. Some have regulatory role, some involved in prolonging inflammation, and others kill infected host cells. All carry antigen receptors and undergo clonal selection, expansion, differentiation into memory cells and defensive ...

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