β2-microglobulin (β2M) is a small protein playing a critical role in stabilizing major histocompatibility complex class I (MHC-I) molecules on nucleated cells. Elevated levels of β2M have been observed in several cancers, inflammatory and autoimmune conditions, and renal failures. High concentrations of β2M were reported to inhibit in vitro generation of functional dendritic cells (DCs). However, our findings showed that β2M exerts a negative effect on DCs only when contaminated with endotoxins. We found that β2M preparations with a high level of endotoxin impurities matured DCs, but that this effect was not seen with functional β2M preparations with low levels of endotoxin impurities, thus showing the maturation effect was due to endotoxin stimulation. We confirmed that the high-level endotoxin β2M compromised the in vitro differentiation of monocytes into DCs. In contrast, a low-level endotoxin β2M had no negative impact on DC differentiation nor prevented their maturation and functionality. Moreover, regardless of the levels of endotoxin impurities, β2M stabilized the expression of MHC-I molecules, confirming its functionality in the experimental settings. Our results show that β2M does not compromise the differentiation of DCs and indicate that elevated levels of β2M are unlikely to negatively regulate the immune system. These results have significant implications for understanding the functions of high β2M concentrations in clinical contexts and in vitro applications.

Department of Immunology 2nd Faculty of Medicine Charles University and Motol University Hospital Prague Czech Republic cuni cz

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