Determination of the dose-response curve for rabbit leucocytic pyrogen reveals a hyperthermic "ceiling" at which there is a marked insensitivity to dosage. This finding has important implications in relation to the quantitative assay of leucocytic pyrogen.
Polymorphonuclear leucocytes separated from normal rabbit blood possess the capacity to produce less than 5 per cent of the pyrogen generated by the same number of rabbit granulocytes collected from acute peritoneal exudates.
Blood granulocytes, separated in the cold from the buffy coat, contain no detectable preformed pyrogen.
The amount of preformed pyrogen within exudate granulocytes represents but a small fraction of the pyrogen which the cells are capable of generating when incubated in normal saline at 37°C. It is suggested that the active pyrogen is formed from an inactive precursor within the cells.
Under the conditions tested, cell fragments of rabbit granulocytes fail to produce endogenous pyrogen.
The fact that the production of pyrogen is blocked at 4°C is in keeping with the hypothesis that it involves metabolic reactions within the cell.