CD101: A versatile molecule associated with immunoregulatory and antimicrobial functions

CD101 is a disulfide-linked immunoglobulin-like glycoprotein with a unique glutamine-tryptophan-isoleucine sequence motif. Allelic variations within the Cd101 gene can influence CD101 expression and function of different myeloid cell and T lymphocyte populations. CD101 serves also as maturation marker for neutrophils and differentiation marker for dendritic cell (DC), eosinophil, and T cell subsets. While the numbers of CD101-expressing eosinophils and T lymphocytes increase in certain chronic disorders, DCs, macrophages, and neutrophils with reduced expression of this transmembrane molecule are transiently observed during acute inflammation, cytokine exposure, or bacterial infection. Indeed, cell-specific expression of CD101 correlates with different functional responses and cellular phenotypes in various settings including Mycobacterium tuberculosis and viral infections, allergic disorders, and cancer immunotherapy. Importantly, myeloid cells and regulatory T cells mediate more powerful protection against experimental enterocolitis and type 1 diabetes when they both express CD101. In contrast, CD101 expression on eosinophils is associated with enhanced inflammatory responses. Moreover, CD101-expressing neutrophils limit bacterial infections better than CD101-deficient cells. Thus, CD101 simultaneously contributes to the restriction of microbial infections and the regulation of immune-mediated tissue damage. However, the mechanisms underlying the diverse functions of CD101 as well as the general biological role of CD101 have not been characterized yet. Moreover, the factors contributing to the regulation of CD101 expression remain unknown. Here, we review current information about the immune-modulatory and antimicrobial functions of CD101. Moreover, we discuss the potential role of CD101 as biomarker for inflammatory and infectious diseases and as predictor for the outcome of cancer immunotherapy.