The role of Fas in the homeostatic regulation of CD8+ T cells after antigen challenge was analyzed in the murine model of lymphocytic choriomeningitis virus (LCMV) infection. Mice homozygous for the lpr mutation and carrying T cell receptor (TCR) alphabeta transgenes specific for the LCMV glycoprotein peptide aa 33-41 in the context of H-2Db were used. Five main results emerged: first, development of lymphadenopathy and of CD4- CD8- double-negative B220+ T cells in lpr mice was not inhibited by the alphabeta TCR transgenes; second, tolerance induction and peripheral deletion of CD8+ T cells induced by LCMV glycoprotein peptide injection was independent of Fas expression; third, clonal down-regulation of Fas-deficient TCR-transgenic CD8+ T cells after acute LCM virus infection was identical to the decline of transgenic T cells expressing Fas; fourth, in vivo activated CD8+ effector T cells from TCR transgenic and TCR-lpr/lpr mice were equally susceptible to activation-induced cell death in vitro; and fifth, transgenic effector T cells from lpr/lpr mice were cleared in the declining phase of the immune response in vivo without giving rise to CD4- CD8- double-negative T cells. Taken together, these data suggest that the homeostatic regulation of CD8+ T cells after antigen challenge in vivo is regulated by mechanisms that do not require Fas.

Perforin‐mediated lysis and secretion of IFN‐γ belong to the key effector functions of CD8 T cells. To compare the anti‐tumor activity of these two mechanisms, we used B16.F10 melanoma cells (B16GP33) expressing the cytotoxic T cell epitope GP33 and T cell receptor transgenic (TCR‐tg) mice specific for GP33 and deficient in perforin or IFN‐γ. B16GP33 tumor cells, injected either i. v. to induce experimental metastases or s. c., were similarly controlled in both wild‐type and perforin‐deficient, but not in IFN‐γ‐deficient TCR‐tg mice. A similar result was obtained when the therapeutic efficacy of adoptively transferred TCR‐tg effector cells from these mice was examined in the corresponding perforin‐ or IFN‐γ‐deficient C57BL / 6 hosts. Criss‐cross experiments further revealed that IFN‐γ production by the host strongly influenced the efficiency of the adoptively transferred effector cells. In contrast to the potent ability of GP33‐specific effector cells to mediate B16GP33 tumor regression without perforin, GP33‐specific memory cells, induced with recombinant vaccinia virus expressing GP33, failed to control B16GP33 tumor growth in the absence of perforin. In conclusion, our data demonstrate a crucial role for IFN‐γ in B16GP33 tumor cell elimination in vivo and indicate a differential requirement of perforin by effector versus memory CD8 T cells in anti‐tumor immunity.

SUMMARYThe deposition of antigens and immune eomplexes (IC) in the renal glomerulus is charge-dependcnl. The demonstration that molecules of nei anionic charge, but with discrete positively charged regions, exhibit affinity for the glomerular basement membrane (GBM) extends this concept. Charge hybrid (polar) molecules were constructed by covalently coupling small polycations (lysozyme or linear poly-L-lysine chains with a mean of 17 and 20 residues) to larger polyanions (ovalbumin or human scrum albumin (HSA)). Although the products were of overall net anionic charge they still bound to glomerular structures. ImmunoHuorcscence studies performed after I.v. injection ofthe samples into rats revealed that HSA;poiy-L-Iysine had the highest atfinity. Radioisotopic measurements showed uptake of HSA: poly-L-lysine to be a function of the number of lysine residues; binding of HSA: poly-L-lysine:u was 2-5 times higher than HSA:po!y-L-Iysinen iPmeruli within 12 h. Administration of HSA :poiy-L-lysine followed by anti-HSA antibody induced immune complex formation in the capillary wall, giving rise to a granular immunofluorescence pattern and discrete subendotheliai and subepithelia! deposits. Molecules with polar structure do occur naturally and may contribute to immune eomplex formation in glomerulonephritis.