Poulsen, S. E. | Search bioRxiv

bioRxiv2025

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.

immunology↗

bioRxiv2025

Beta-2-microglobulin stimulates neutrophil phagocytosis of bacteria and apoptotic cells

Efficient clearance of dead cells and pathogens is essential for survival and requires both the innate and adaptive immune systems. Polymorphonuclear leukocytes (PMNs, predominantly consisting of neutrophil granulocytes) constitute an important first line of defense. These highly specialized cells can phagocytose pathogens and clear apoptotic cells through efferocytosis. Beta-2-microglobulin ({beta}2m) serves as the light chain of major histocompatibility complex class I (MHC I) molecules, associating non-covalently with the heavy transmembrane chain that binds and presents antigenic peptides to CD8+ T cells. This represents the canonical role of {beta}2m. {beta}2m is also found in the granules of PMNs and is released into the extracellular space during degranulation. However, a specific function for {beta}2m in the context of PMN function or degranulation has not yet been identified. We now present evidence that {beta}2m is of importance for both phagocytosis of pathogens and efferocytosis of dead cells by PMNs. The addition of exogenous {beta}2m (50 mg/l) to PMNs in the presence of latex beads increased the phagocytic activity from 23% to 31%. Furthermore, both {beta}2m and desLys58-{beta}2m (dK58{beta}2m) enhanced phagocytosis of Gram-negative and -positive bacteria by more than 3.6-fold, though no effect was observed with zymosan bioparticles. Maintaining tissue homeostasis requires the continuous generation of new cells and the efficient clearance of apoptotic cells through efferocytosis. Treatment with {beta}2m or dK58{beta}2m led to a dose-dependent increase in efferocytosis of apoptotic Jurkat cells, reaching up to a two-fold enhancement. This effect was comparable to that obtained by GM-CSF, used as a positive control. In all cases, cytochalasin D blocked {beta}2m-mediated uptake in PMNs. These data demonstrate that {beta}2m can be of importance in phagocytosis of bacterial pathogens as part of the innate immune response and tissue homeostasis by removing dead cells by efferocytosis.

immunology↗