Regulatory effects of beta-2-microglobulin on reactive oxygen species generation in polymorphonuclear cells

Beta-2-microglobulin ({beta}2m) constitutes the invariant light chain of the major histocompatibility complex class I (MHC I) and is present on all nucleated cells, as well as in biological fluids, platelets and neutrophil granules. Immune cells can increase their production and secretion of {beta}2m in response to cytokines such as IFN-{gamma}, IFN-, and TNF-. Elevated {beta}2m levels can be detected in various inflammatory, autoimmune, infectious and malignant diseases, often correlating with poor prognosis and reduced survival. So far, no specific functions have been agreed on for soluble {beta}2m. In the present study, we investigated the effects of exogenous {beta}2m and two proteolytically processed forms, cK58{beta}2m and dK58{beta}2m, on ROS production in polymorphonuclear leukocytes (PMNs). {beta}2m was shown to enhance ROS generation triggered by latex beads, while cK58{beta}2m and dK58{beta}2m suppressed both baseline ROS levels and responses to latex beads, TNF-, and fMLF. Among these, dK58{beta}2m was generally the most potent inhibitor. The inhibitory effect of cK58{beta}2m and dK58{beta}2m was also confirmed in DMSO-differentiated HL-60 cells, a neutrophil-like cell line. Furthermore, treatment with dK58{beta}2m impaired the recruitment of p47phox and p67phox to the plasma membrane following fMLF stimulation, two key subunits of the NADPH oxidase complex responsible for superoxide anion production in neutrophils. This may explain the reduced ROS production observed in cells treated with dK58{beta}2m. Taken together, these results suggest that {beta}2m, cK58{beta}2m and dK58{beta}2m can regulate ROS generation in PMNs and highlight a potential role for {beta}2m in modulating the innate immune response through control of ROS production.