The effects of thermal injury on serum interleukin 1 activity in rats

Interleukin 1 (IL-1) is present in the blood of burned patients but its pathophysiologic role is not fully understood. Rat models would be useful research tools, if this cytokine could be identified in a complex fluid like blood. We describe a methodology, which revealed IL-1 activity from the serum of burned rats. Serum was collected from 37 rats with 30% total body surface burns and 9 unburned controls. To vary the burn response, the wounds of 17 rats were seeded with nonvirulent Pseudomonas aeruginosa at the time of injury. IL-1 activity was assessed by its capacity to induce IL-2 secretion in murine lymphoma cells (LBRM-33-1A5). Only after the serum had been fractionated, concentrated, and dialyzed, was IL-1 activity uncovered. Sera from burned rats contained five times more IL-1 activity than those from control animals (p < 0.05). There was no difference in serum IL-1 activity between burned and burn-seeded animals. The IL-1 activity was heat labile, and not produced by P. aeruginosa endotoxin, TNF-alpha, or endogenous IL-2 in rat serum. These results confirm that serum IL-1 levels are increased following thermal injury, and that there is no apparent relationship between IL-1 levels and infection. The serum preparation scheme presented in this study offers a reasonable approach to the measurement of serum IL-1 levels in rat models of disease and injury.