Effect of mycophenolate mofetil (RS-61443) on cytokine production: inhibition of superantigen-induced cytokines.

The effects of the immunosuppressant mycophenolate mofetil (MPAM, RS-61443) on cytokine production at the single cell level were assessed using in vitro activated human mononuclear cells. Cytokine production was studied with UV microscopy of fixed and permeabilized cells stained with cytokine specific monoclonal antibodies (mAbs). The cytokines evaluated included interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10 interferon gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), TNF-beta, and granulocyte macrophage-colony stimulating factor (GM-CSF). MPAM exhibited a marked antiproliferative effect without cytotoxicity in all mononuclear cell cultures. Six to 24 hours after stimulation with the superantigen Staphylococcus aureus enterotoxin A (SEA), most cytokine production was unaffected by MPAM at therapeutic concentrations (10(-6) M), with the exception of GM-CSF. In contrast, by 48 h after antigen activation, MPAM significantly inhibited all studied cytokine production (p < 0.05). Cyclosporin A (CsA), used as a control at a concentration of 100 ng/ml, inhibited production of all studied cytokines, at all time points. Monokine production after lipopolysaccharide (LPS) stimulation was unaffected by MPAM. Similarly, the production of most of the cytokines studied after mitogen stimulation with phorbol ester (PMA) plus calcium ionophore (ionomycin) was not affected by MPAM, in comparison to CsA which demonstrated significant inhibition of all cytokines tested under these conditions. However, a late inhibitory effect on IL-3 production was seen by MPAM at 48 h after mitogenic stimulation. Further observations are required to explain the divergent results on cytokine production by MPAM in superantigen-activated and mitogen-activated human mononuclear cells.