IL-32 induces indoleamine 2,3-dioxygenase+CD1c+ dendritic cells and indoleamine 2,3-dioxygenase+CD163+ macrophages: Relevance to mycosis fungoides progression

Mycosis fungoides (MF) progresses from patch to tumor stage by expansion of malignant T-cells that fail to be controlled by protective immune mechanisms. In this study, we focused on IL-32, a cytokine, highly expressed in MF lesions. Depending on the other cytokines (IL-4, GM-CSF) present during in vitro culture of healthy volunteers' monocytes, IL-32 increased the maturation of CD11c+ myeloid dendritic cells (mDC) and/or CD163+ macrophages, but IL-32 alone showed a clear ability to promote dendritic cell (DC) differentiation from monocytes. DCs matured by IL-32 had the phenotype of skin-resident DCs (CD1c+), but more importantly, also had high expression of indoleamine 2,3-dioxygenase. The presence of DCs with these markers was demonstrated in MF skin lesions. At a molecular level, indoleamine 2,3-dioxygenase messenger RNA (mRNA) levels in MF lesions were higher than those in healthy volunteers, and there was a high correlation between indoleamine 2,3-dioxygenase and IL-32 expression. In contrast, Foxp3 mRNA levels decreased from patch to tumor stage. Increasing expression of IL-10 across MF lesions was highly correlated with IL-32 and indoleamine 2,3-dioxygenase, but not with Foxp3 expression. Thus, IL-32 could contribute to progressive immune dysregulation in MF by directly fostering development of immunosuppressive mDC or macrophages, possibly in association with IL-10.