Synovial inflammatory response to bacterial endotoxin.

The ability of bacterial endotoxins to produce local inflammation has been recognized as one of the many biologic activities of these intriguing products of the gram-negative bacterial cell.1" This property of endotoxin, however, has not been studied extensively with the highly purified materials now available. Preliminary observations are reported here on the inflammatory response elicited by intra-synovial injections of endotoxin into rabbit suprapatellar bursae. These studies were designed to determine the sensitivity of this technique for detecting endotoxin contamination as a possible cause of the inflammatory reaction produced by intra-synovial injection of foreign proteins.' Because the synovial cavity proved extremely reactive to endotoxin-induced inflammation, the initial observations were expanded and compared with other known biologic properties of endotoxin. Repeated intravenous injections of endotoxin produce a relative resistance to many of its biologic effects, particularly the ability to produce fever and to cause death. This relative resistance has been termed 'tolerance' to endotoxin.' The inflammatory reaction in 'tolerant' rabbits was of particular interest.