The Adaptive Immune Response

Publisher Summary B cells and T cells comprise the adaptive immune system, which allows an individual to develop a specific response to an infection (antigen) and retain memory of that infection. Memory allows for a faster and more robust response if that same infection occurs again. The adaptive immune response is divided between two components: humoral immunity which is mediated by antibodies produced by B lymphocytes (B cells) and cell-mediated immunity, which is mediated by T lymphocytes (T cells). T cells can directly kill infected cells or activate other cells, like macrophages, to kill or phagocytize infected cells. T cells are also often needed to “help” B cells mount an antibody response. The other major mechanism of host defense is the innate immune system. In contrast to adaptive immunity, innate immunity is not antigen specific, functions to recognize microorganisms, works very quickly (within hours), and is mediated by other cellular mechanisms. The body, through pattern recognition receptors such as Toll-like receptors, recognizes these organisms. Once recognized, invading microorganisms can be attacked by circulating antibodies, opsonized and killed by complement activation, or phagocytized by macrophages. This chapter focuses on the adaptive immune response and how its components interact with bone.