The incidence of skin rashes or erythema multiforme to sulfamethoxazole in exposed patients is about 3%. Among patients with acquired immunodeficiency syndrome the risk is ≈ 10 times higher. The pathogenesis of these reactions and the reason for the increased frequency in HIV infections are not understood.Objective
To investigate drug specific T-cell-mediated cytotoxicity in sulfamethoxazole-induced skin reactions.Methods
Specific T-cell lines and T-cell clones generated from a donor who developed a skin rash to sulfamethoxazole were assessed with a standard 4 h 51Cr cytotoxicity assay in the presence or absence of soluble sulfamethoxazole. B lymphoblasts and keratinocytes with and without interferon gamma pretreatment were used as target cells. Selective blockers of FasL/Fas and perforin-mediated killing and immunostaining for perforin were used to evaluate the involvement of the different cytolytic pathways.Results
CD4+ and CD8+ sulfamethoxazole specific T-cell clones showed a drug-specific and MHC-restricted cytotoxicity against autologous B lymphoblasts in the presence of soluble sulfamethoxazole. Keratinocytes, if pretreated with interferon gamma, were specifically killed predominantly by CD4+ T-cell clones. Specific T-cell clones of both CD4+ and CD8+ phenotype showed a strong immunoreactivity for perforin and the cytotoxicity was blocked by concanamycin A which suggests a perforin-mediated killing.Conclusion
Perforin-mediated killing of autologous keratinocytes in the presence of soluble sulfamethoxazole by drug-specific CD4+ lymphocytes may be a pathway for generalized drug-induced delayed skin reactions. The requirement of interferon gamma pretreatment of keratinocytes for efficient specific killing might explain the increased frequency of drug allergies in generalized viral infections like HIV, when interferon gamma levels are elevated.