Endotoxin-induced release of colony-stimulating activity in man.

Six healthy adult volunteers were injected intravenously with Pseudomonas endotoxin (Piromen) to determine effects on serum colony-stimulating activity (CSA). Serum was assayed with a double-layer agar cloning technique using normal human bone marrow as the target cell preparation. A marked increase in serum CSA was noted after endotoxin administration lasting up to 180 min. The colonies formed in response to postendotoxin serum were smaller than those seen with leukocyte feeder layers but were otherwise morphologically normal. These studies suggest that granulopoietic humoral factors may be modulated in man by endotoxin administration.