One early reaction of the host to infection with protozoan parasites is the secretion of an array of potent cytokines including tumor necrosis factor (TNF), interleukin (IL-1) and IL-6. The combined action of these cytokines causes fever, leukocytosis and the production of acute phase proteins such as C-reactive protein (CRP). These early responses contribute significantly to the outcome of infection by influencing the course of infection directly and by regulating the specific immune response to the parasite.