Inhibition of cytokine production and interference in IL-2 receptor-mediated Jak-Stat signaling by the hydroxylamine metabolite of sulfamethoxazole

Sulfonamides, used for the treatment of opportunistic infections in immunoc ompromised patients, are associated with a high incidence of adverse drug e vents, including severe hypersensitivity reactions. Imbalances in the produ ction and detoxification of reactive sulfonamide metabolites have been impl icated in the pathogenesis of these life-threatening reactions. The hydroxy lamine metabolite of sulfamethoxazole (SMX-HA) inhibits the proliferation o f mitogen-stimulated peripheral blood mononuclear cells (PBMCs) in vitro wi thout reducing Interleukin 2 (IL-2) expression. We investigated the effects of SMX-HA on accessory cytokine expression and IL-2 receptor (IL-2R) media ted signal transduction. SMX-HA did not reduce significantly mRNA productio n of proinflammatory [tumor necrosis factor alpha (TNF-alpha) and IL-1 beta ], Th1-type (IFN-gamma), Th2-type cytokines (IL-4 and IL-10). Sublethal con centrations of SMX-HA (25 muM) reduced significantly the production of TNF- alpha, IL-1 beta, and IL4 protein without inhibiting the production of IFN- gamma. This finding suggests that exposure to SMX-HA might direct a respons e towards a Th-1 vs. a Th-2 response. Immunoblot analysis of IL-2R-mediated Janus kinases and signal transduction activators of transcription (Jak-Sta t) signal transduction revealed diminished phosphorylation of Jak1 and Jak3 and inhibited downstream phosphorylation of Stat3, Stat5a, and IL-2R gamma in phytohemagglutinin/rIL-2 activated PBMCs treated with SMX-HA. SMX-HA di d not inhibit Jak association with IL-2R gamma or IL-2R beta. These data il lustrated that sublethal concentrations of SMX-HA interfere with IL-2R-medi ated signal transduction, resulting in altered cytokine production and inhi bition of lymphocyte proliferation.