Expanding the List of Dysregulated Immunosuppressive Cells in Psoriasis

Traditionally, myeloid-derived suppressor cells (MDSC) have been studied in regard to their increased numbers of circulating cells in cancer patients. Recent research efforts have also increased awareness of MDSC in non-malignant inflammatory diseases, including asthma, inflammatory bowel disease, and arthritis. Psoriasis can now be added to the growing list of inflammatory disorders with an MDSC component. Cao et al. report increased numbers of monocytic myeloid-derived suppressor cells (Mo-MDSC) in psoriasis patients and examine the implication of dysregulated Mo-MDSC function. Cao et al. describe psoriatic Mo-MDSC that produce increased IL-23, IL-1b, and CCL4 cytokines compared to Mo-MDSC from healthy controls. These results complement previous research demonstrating psoriatic Mo-MDSC are unable to suppress autologous and heterologous CD8 T-cell proliferations, display decreased expression levels of PD-1 as well as PD-L1, and fail to produce effective immuno-competent regulatory T cells (Tregs). Cao et al. also identify the unique expression of the surface protein DC-HIL on psoriatic Mo-MDSC. The expanded population of DC-HIL(+) Mo-MDSC in psoriasis patients, however, display inferior suppressive capabilities compared to DC-HIL(+) Mo-MDSC found in melanoma patients, suggesting contextual signaling as a potential contributing factor to Mo-MDSC function.