Mice homozygous for lpr or gld develop lymphoproliferative disease characterized by the progressive accumulation of functionally impaired B220+ double-negative (DN) T cells and primed CD4+ and CD8+ T cells. The mechanisms leading to the accumulation of these T cells subsets are poorly understood but are clearly dependent on lack of expression of Fas in lpr mice and expression of defective FasL in gld mice. A role for V beta 8+ T cells also has been reported. Recently, a variety of experimental approaches revealed that the majority of B220+ DN T cells are derived from MHC class I-selected CD8+ precursors. Here we used the potent mitogen, staphylococcal enterotoxin B (SEB): (i) to examine the effects of defective Fas-FasL expression on the deletion of peripheral V beta 8+ T cells in 6- to 8- and 20-week old C3H-lpr and -gld mice, (ii) to determine the immunocompetence of B220+ DN T cells in vivo, and (iii) to determine if activated V beta 8+ CD8+ T cells can differentiate into B220+ DN T cells. The role of V beta 8+ T cells in the accumulation of B220+ DN T cells also was reinvestigated. These studies showed that deletion pathways independent of Fas-FasL expression function in young lpr and gld mice and delete CD4+ T cells more efficiently than CD8+ T cells. As the mice age, these alternative pathways become less effective and this may explain the progressive accumulation of memory T cells. No abnormalities in tolerance induction were observed in young or diseased mice. Stimulation of +/+, lpr and gld V beta 8+ CD8+ T cells induced the expression of B220. B220 levels were maximal 2 days after SEB and were undetectable 5 days later, suggesting that B220 is a transiently expressed activation marker on CD8+ T cells. Neither the B220+ V beta 8+ CD8+ T cells nor other V beta 8+ T cell populations converted with detectable frequency into B220+ DN T cells after single or multiple doses of SEB. B220+ DN T cells, which are functionally anergic in vitro, did not proliferate or undergo deletion after SEB stimulation indicating that these cells also are functionally impaired in vivo. In contrast to previous reports, chronic elimination of V beta 8+ T cells had no effect on the accumulation of B220+ DN T cells.(ABSTRACT TRUNCATED AT 400 WORDS)