Complement and the pathogenesis of endotoxic fever

Our results to date are consistent with the hypothesis that pyrogenic doses of LPS, particularly if injected i.p., rapidly activate the complement cascade and that at least one of the components generated, C5, contributes critically to the induction of the febrile response. We speculate that it causes the quick release of a mediator capable of stimulating local, primary sensory nerve terminals that convey the pyrogenic message to the POA. The exact cell source and nature of the mediator thus released remain to be elucidated. The answers should be very helpful in clarifying the sequence of events triggered by the sudden invasion of the body by infectious pathogens and point, perhaps, to ways in which the particularly untoward effects of such an invasion might be mitigated therapeutically. The present data also indicate that the signals that initiate fever differ according to the nature of the exogenous pyrogen [LPS, muramyl dipeptide, poly(I)·poly(C) and, by extension, the original microorganisms from which these compounds are derived], its dose and route of administration (i.v., i.p., etc.), and the species (and even strain) affected. Other studies have shown previously that the time of day, the ambient temperature, the age of the challenged host, the nutritional status, and other factors may influence febrile responsiveness. Hence, the processes underlying the febrile response are diverse and complex. While this is not a novel conclusion in itself, it nevertheless bears repeating as a cautionary reminder to distinguish between the various stages and inducers of fever when studying the mechanisms that modulate the febrile course and to avoid undue generalizations from particular findings. © ISB 2000.