Neutrophil beta-2 microglobulin: an inflammatory mediator

Beta-2 microglobulin (beta 2m) constitutes the light invariant chain of HLA class I antigen, and is a constituent of mobilizable compartments of neutrophils. Two forms of beta 2m exist: native beta 2m and proteolytically modified beta 2m (Des-Lys58-beta 2m), which shows alpha mobility in crossed radioimmuno-electrophoresis. The modification of native beta 2m can be executed by membrane-associated activity of mononuclear cells, and Des-Lys58-beta 2m augments the production of interleukin 2. In this study we present evidence that human neutrophils contain native beta 2m in specific granules, secretory vesicles, and plasma membrane. Beta 2m was released in the native form from neutrophils in response to stimulation with chemotactic stimuli and phorbol ester. The results of experiments designed to study the modification of native beta 2m by neutrophils indicated that neutrophils do not participate in the proteolysis of beta 2m. However, we demonstrated that native beta 2m following degranulation may be transformed to Des-Lys58-beta 2m by lymphocytes. We suggest that neutrophil beta 2m following exocytosis may be transformed to Des-Lys58-beta 2m, acting as an extracellular messenger between granulocytes and lymphocytes in the inflammatory focus.