Components of the Immune System

Detection of infection is mediated by the innate immune system, triggering a series of events designed to limit the spread of infection while at the same time activating the adaptive immune system. The innate immune system can discriminate different types of infection, but does not provide immunological memory, namely prior exposure to an infection will not alter future innate immune responses to the same infection. In contrast, activation of the adaptive immune system does generate immunological memory. The effector arms of the adaptive immune system are humoral immunity (namely antibody, produced by B cells) and cell mediated immunity (production of cytokines and cell killing by T cells). Both of humoral and cell mediated immunity are highly specific and tightly regulated by cytokines. Immunological memory is a result of selective expansion of subpopulations of B cells and T cells, providing rapid protection against future infection. It is this process that can be exploited by vaccination to generate protection without disease.