In vitro immunosuppressive effects of methotrexate and azathioprine on Langerhans cells

The long-term use of immunosuppressive agents may cause profound suppression of the cutaneous immune function. Because epidermal Langerhans cells (LC) play an important role in the cutaneous immune system, they could be the target of immunosuppressants. Since little information is available about the direct immunosuppressive effects of methotrexate (MTX) and azathioprine (AZA) on LC, we studied the viability and immunostimulatory effects of purified LC after pulsation with MTX or AZA at various concentrations. Both MTX and AZA started to suppress the mixed LC-T lymphocyte reaction (MLCLR) significantly at a concentration of 1 microgram/ml. However, the suppressive effect of MTX was not dose-dependent; no further suppression was seen up to a concentration of 1 mg/ml. MTX showed no inhibitory effect on the viability of LC even at concentrations as high as 1 mg/ml. In contrast, the suppressive effect of AZA on the MLCLR was dose-dependent and AZA at a concentration of 500 micrograms/ml or higher markedly decreased the viability of LC. Our study confirmed the immunosuppressive effect of MTX and AZA on epidermal LC. In comparison to MTX, AZA at pharmacological levels showed stronger inhibitory effects on alloantigen-presenting capacity of human epidermal LC and was more cytotoxic to LC. In the therapeutic range, however, MTX and AZA probably have no direct effect on epidermal LC. Our study supports the notion that long-term immunosuppressants deplete cutaneous LC by bone marrow suppression.