Fever and immunoregulation: hyperthermia, interleukins 1 and 2, and T-cell proliferation.

The role of fever in host defense, if indeed it has one, is poorly understood. Fever in response to exogenous agents is mediated by a host macrophage product called endogenous pyrogen (EP). Recently it has been shown that EP is probably identical to interleukin 1 (IL1), an immunostimulatory macrophage product that induces T-cell proliferation. We postulated that the pyrogenic and immunostimulatory actions of this host mediator might be interrelated and tested T-cell proliferation induced by IL1 at a temperature characteristic of fever. The T-cell proliferative response to IL1 (and to the lymphokine, interleukin 2) was greatly increased at 39 degrees C compared to 37 degrees C, while B-cell mitogenesis in response to lipopolysaccharide was not. These findings suggest that, if similar events occur in vivo, fever may have important immunoregulatory significance and call into question the current indiscriminate use of antipyretic agents.