Humoral immunity is so named because it involves substances found in the humours, or body fluids. It is mediated by antibodies produced by cells of the B lymphocyte lineage. B cells, activated by the adaptive immune responses, transform into plasma cells which secrete antibodies. This process is aided by CD4+ T-helper 2 cells, which provide active co-stimulation. The secreted antibodies bind to antigens present on the surfaces of invading microbes, which marks them for subsequent destruction (Pier et al., 2004). Another important function of antibodies is to initiate the "complement destruction cascade." .
