Proinflammatory effects of interleukin 1 in the rat air pouch

We have utilized the 6-day air-pouch model in rats to study the local tissue response to interleukin-1 exposure. Injection of either recombinant human interleukin 1 alpha (rIL-1 alpha) or interleukin 1 beta (rIL-1 beta) directly into preformed air pouches caused a 10- to 100-fold increase in the number of white blood cells present within the pouch. On a weight basis, rIL-1 beta was more active than rIL-1 alpha. Polymorphonuclear neutrophils (PMN) represented the majority of cells entering the pouch following either a single injection or repeated daily injections of rIL-1 alpha or rIL-1 beta. Significant increases in the number of mononuclear cells present were observed only following repeated injections. Repeated injections of rIL-1 beta, but not rIL-1 alpha, also caused the accumulation of large amounts of fluid within preformed pouches and a grossly apparent thickening of the connective-tissue lining of the pouch. Microscopic examination of stained sections of pouch lining tissue indicated a proliferation of the connective-tissue elements of the lining and deposition of large quantities of extracellular collagen within the pouch wall. These findings are entirely consistent with a role for interleukin 1 in the development and perpetuation of inflammatory reactions.