Production of pyrogen by polymorphonuclear leukocytes during the course of casein-induced peritonitis in rabbits

Rabbits with casein-induced peritonitis were febrile only during the early stage (1.5 to 12 hours) of inflammation. At that stage, peritoneal exudate cells (PEC) had preformed endogenous pyrogen (EP), while blood leukocytes and leukocytes obtained at the later stage of the inflammatory process did not. Early PEC consisted of 99% polymorphonuclear leukocytes (PMN). As early PEC and highly purified PMN (almost 100% pure) released almost identical amounts of EP, we concluded that PMN were the EP-producing cells in the early PEC. EP from PMN of rabbits was composed of three factors with similar molecular weight (8,000 to 18,000) but different pI values (pI 7.2, 5.4, and 4.5). EP in the three fractions could not be separated from thymocyte comitogenic factor (TMF) in terms of m.w. and pI values. About 60% of EP activity and 92% of TMF activity in the culture supernatant were present in the pI 7.2 fraction. The pI 7.2 factor was weaker in EP activity and stronger in TMF activity than the other acidic fractions (pI 5.4 and 4.5). After high purification, 42 ng of the pI 7.2 factor had one unit of EP activity: one unit of TMF activity was present in 126 pg of highly purified pI 7.2 factor.