An anti-inflammatory substance in normal human plasma.

A substance of low molecular weight, below 1000 daltons, has been separated from normal human plasma by a stepwise process involving ultrafiltration followed by column chromatography. The spectrum of anti-inflammatory activity of the active fraction in a variety of animal models shows that it is most active in situations in which the emigration of circulating leucocytes plays the more prominent role. The fraction exerts a selective action on the release of chemotactic factors after the activation in vitro of the complement cascade by the alternate but not by the classical pathway. The existence of the plasma fraction raises several interesting queries. Is it part of the naturally occurring control mechanisms in inflammation? What is its relevance to human disease, e.g., rheumatoid arthritis, and do conventional antirheumatic drugs interact with it? Does its lack of activity against chemical mediators of inflammation and their generating systems throw any light on the importance of these materials in inflammatory reactions?