The pyrogens of myxoviruses I. Induction of hyperthermia and its tolerance

Abstract

The minimal effective dose of influenza A virus (strain PR8) capable of inducing fever on intravenous administration to adult rabbits is 0.2 μg. On the basis of the febrile response to reinjection, the myxoviruses can be divided into two subgroups. While all members of the group are capable of inducing tolerance to the pyrogenic effect of influenza, parainfluenza, and mumps viruses, none is effective against challenge by NDV and fowl plague virus. The characteristic difference holds for all the numerous strains tested. After prolonged daily injections of NDV, partial homologous tolerance can be induced. During the stage of hyperthermia an endogenous pyrogen is present in the blood, capable of inducing fever in both normal recipients and animals tolerant to the action of viral pyrogens. Accordingly, tolerance to viral pyrogens cannot rest either on incapacity to respond to endogenous pyrogens or on interference with their action, but rather on the blocking of a stage preceding their liberation. Unlike bacterial pyrogens, comparable doses (in terms of the febrile response they provoke) of viruses do not produce a Shwartzman reaction.