IL-10 inhibits ICAM-1 expression on human Langerhans cells but not on keratinocytes, dermal endothelial cells or fibroblasts.

Intercellular adhesion molecule-1 (ICAM-1) is regularly expressed or inducible on all major cutaneous cell populations including Langerhans cells, keratinocytes, endothelial cells and dermal fibroblasts. ICAM-1 is induced in the skin under inflammatory conditions and plays an important role in the activation of T cells. Interleukin-10 (IL-10) is a pluripotent immunosuppressive cytokine that inhibits proliferation of T cells via inhibition of antigen-presenting cells including Langerhans cells. We demonstrates that IL-10 inhibits baseline and also cytokine-stimulated ICAM-1 expression on human Langerhans cells, which has previously been shown in the murine system. No effect of IL-10 was seen on human dermal vascular endothelial cells, which like Langerhans cells are also able to present antigen. Additionally, no inhibitory effect of IL-10 was observed on the ICAM-1 expression of keratinocytes and dermal fibroblasts. As IL-10 only weakly suppresses MCH II on human Langerhans cells, inhibition of ICAM-1 and other accessory molecules by IL-10 seems to be an important mechanism inhibiting the antigen-presenting function of human Langerhans cells.

Human epidermal Langerhans' cells are targets for the immunosuppressive macrolide tacrolimus (FK506).

BACKGROUND: The immunosuppressive macrolide tacrolimus (FK506) has been shown to inhibit allergic contact dermatitis in animal models as well as in human beings. More recently, successful treatment of atopic dermatitis with an ointment containing tacrolimus has been reported. OBJECTIVES: We explored the effects of this compound on epidermal Langerhans' cells (LCs), which are known to play an important pathophysiologic role in inflammatory skin diseases. METHODS: The expression of the intracellular FK506 binding protein (FKBP12) was monitored on freshly isolated and cultured epidermal LCs. Phenotyping and functional exploration of LCs treated with different concentrations of tacrolimus and beta-methasone valerate (betaMv) were performed. RESULTS: FKBP12 is expressed in freshly isolated LCs but is lost while they are maturating into mature dendritic cells. Tacrolimus inhibited the expression of IL-2R (CD25) and of the costimulatory molecules CD80 (B7.1) and CD40. Expression of MHC class I and II was also affected, whereas CD86 (B7.2) expression was not altered. In contrast, betaMv strongly increased the expression of CD25. Paradoxically, while decreasing CD40 and MHC class I expression, betaMv significantly increased the expression of MHC class II, CD80, and CD86 on cultured LCs but impaired their allostimulatory activity. Tacrolimus was about 100 times more potent than betaMv at inhibiting LC stimulatory function. CONCLUSION: Tacrolimus can exert immunopharmacologic alterations on LCs, which may account, at least in part, for the therapeutic effect of this compound in eczematous skin diseases.