Pertussis toxin interferes with superantigen-induced deletion of peripheral T cells without affecting T cell activation in vivo: Inhibition of deletion and associated programmed cell death depends on ADP-ribosyltransferase activity

Intravenous injection of a bacterial superantigen such as Staphylococcus aureus enterotoxin B (SEB) causes transient activation and expansion of SEB-reactive Vβ8⁺ T cells, as well as specific down-regulation of the immune response, through partial deletion of superantigen-reactive T cells. Here we demonstrate that co-administration of pertussis toxin (PTX) and SEB reduces the SEB-induced deletion of Vβ8⁺ T cells, although it does not affect T cell activation and proliferation. PTX abrogates the SEB-driven deletion of Vβ8⁺CD4⁺ (not Vβ8⁺CD8⁺) splenocytes that is observed early (12-24 h) after SEB injection. Moreover, it antagonizes the late (≥4 days) deletion of Vβ8⁺CD4⁺ and Vβ8⁺CD8⁺ peripheral T cells that follows transient expansion of such cells. This phenomenon is associated with significant reductions in apoptosis and endonucleolysis and is not caused by a compensatory increase in proliferation of SEB-reactive T cells, as we determined by using a combined fluorometric analysis of cell cycle and DNA alterations, which are associated with programmed cell death. These effects are also observed in thymectomized animals, thus excluding the possibility that PTX might act by enhancing the maturation and export of thymic T cells to the periphery. Moreover, the SEB-induced reduction of Vβ8⁺ splenocytes is antagonized by PTX in vitro. The capacity of PTX to reduce clonal deletion depends critically on its ADP-ribosyltransferase activity, inasmuch as a non-enzymatic PTX mutant fails to act in this biologic system. We conclude that PTX selectively antagonizes or impedes the delivery of negative signals to T cells, which are stimulated by superantigens, without interfering with the transmission of stimulatory signals.