The immune system: cells and molecules for the integration of self and non-self

In a reductionist view, the immune system consists of 4 cell types, 3 diverse receptor systems and 10 to 15 soluble mediators including lymphokines and antibody molecules. Using these elements, the immune system generates 3 different effector mechanisms: Activated macrophages for the killing of intracellular microorganisms, cytotoxic T cells for the killing of virus-infected cells, and antibodies for the neutralization of soluble and cell-associated antigens of various types. While it is already very difficult to derive reliable results form reductionists experiments, such as studying immune responses in culture systems, it is infinitely more complicated to study the influence of physical exercise on the immune system.