The immune system is made up of sets of interacting cells. The first to respond in all cases are the antigen-presenting cells (APCs), which are equipped with receptors for microbial patterns. Engagement of these receptors induces co-stimulatory molecules on the surface of the APCs, and allows it to stimulate potent CD4 T-cell responses, and also CD8 T-cell responses. This in turn leads to B-cell-derived antibody responses. The entire response is controlled by suppressor T cells, as predicted many years ago by Richard Gershon.