Studies in cryptococcal fever. II. Responses of sensitized and unsensitized rabbits to various substances derived from cryptococcal cells.

The cause of fevers induced in rabbits by intravenous injection of cryptococcal cells and soluble extracts was investigated in a previous paper in this series.' Two distinct types of pyrogenic responses were found to be produced by this organism. Intact cells, whether live or killed, caused fevers in normal rabbits, whereas the soluble material induced responses primarily in animals that had been previously exposed to cryptococci or its products. Since some unsensitized rabbits were also found to react to the soluble pyrogen with fever, the present studies were undertaken to investigate further the nature of this material. Evidence is presented that the soluble material from cryptococci contains two different pyrogenic agents, a polysaccharide and a protein, which appear to act by different mechanisms to produce fever.