The localized primary cytotoxic T-cell response to cells expressing minor histocompatibility differences

Lipid-dependent cytotoxicity by the lipase PLRP2 and by PLRP2-positive cytotoxic T lymphocytes (CTLs)

IL-4 induces a lipase, pancreatic lipase related protein 2 (PLRP2), in cytotoxic T lymphocytes (CTLs). Because PLRP2 in semen can mediate lipid-dependent toxicity to sperm, we questioned whether CTL-derived PLRP2 could support similar cytotoxicity toward tumor cells. Recombinant PLRP2 was toxic to P815 tumor cells in 48 h when lipid and another protein, colipase, were present. However, PLRP2-positive CTLs (induced with many lots of IL-4) were unable to mediate lipid-dependent cytotoxicity. Notably, CTLs induced with only one lot of IL-4 had lipid-dependent cytotoxicity. The exceptional lot of IL-4 was effective in multiple experiments at inducing lipid-dependent cytotoxicity. The lipid-dependent cytotoxicity it induced was determined to be perforin-independent. CTLs induced with IL-4 that was unable to induce lipid-dependent cytotoxicity had mRNA for PLRP2 but not mRNA for colipase. Therefore, we added exogenous colipase to the CTL assays but still cytotoxicity was unchanged. We conclude (1) that lipid-dependent cytotoxicity, promoted by the lipase PLRP2 and colipase, will kill tumor cells and (2) that more than PLRP2 alone is required for lipid-dependent cytotoxicity mediated by CTLs.

Further evidence for H-2-unrestricted induction of minor histocompatibility antigens-specific T cell immunity in vivo

Antigenic requirements for inducing minor histocompatibility antigens (MIHA)-specific T cell immunity for second set rejection (SSR) of a MIHA-allogeneic tumor were studied. An intravenous injection of surprisingly small numbers (10(4)-10(5] of live allogenetic spleen cells (SC) effectively primed mice for SSR of the allogeneic tumor, and this immunity was developed as early as 2-3 days after injection of the SC. In contrast, sonication-disrupted allogeneic SC, which should be readily processed by host antigen presenting cells (APC), were not active as immunogens, even at a dose 1000 times higher than the minimum effective dose of live SC. The possibility that host APC preferentially receive MIHA antigens shed by live allogeneic SC for T cell activation was ruled out. These results demonstrated that antigen processing via conventional pathways is very little involved in the mechanism of T cell activation. Under such restricted experimental conditions, the induction phase but not the effector phase of the MIHA-specific T cell immunity was shown to be H-2-unrestricted.

Phenotypic analysis of the inflammatory exudate in murine lymphocytic choriomeningitis

The massive inflammation of the cerebrospinal fluid (CSF) which occurs in adult mice injected with lymphocytic choriomeningitis virus (LCMV) has been analyzed by flow microfluorometry (FMF). The great majority of the T cells detected by direct examination of freshly obtained CSF were found to be Lyt-2+, with an almost total absence of L3T4+ lymphocytes. The Lyt-2/L3T4 ratio of lymphocytes in blood was within normal limits. Predominance of the Lyt-2+ subset was confirmed by culturing the CSF cells after mitogenic stimulation. In addition, the T lymphocytes in CSF of cyclophosphamide-suppressed, virus-infected recipients that had been injected 4 d previously with LCMV-immune spleen cells were almost entirely donor Lyt-2+ cells, while the nonlymphoid elements were exclusively of host origin. However this pattern of donor and host T cell distribution was reversed when the LCMV-infected recipients were not immunosuppressed. The frequency of LCMV-specific CTL precursors in CSF taken immediately before the development of symptoms was as low as 1:3,000 cells. Thus most of the T lymphocytes extravasating into the CSF of mice with LCM are passive participants recruited as a consequence of the function of relatively few LCMV-specific effector T cells. The dominance of the Lyt-2+ T cell subset in the CSF of mice with LCM is intriguing.

Role of the major histocompatibility complex in targeting effector T cells into a site of virus infection

Bone marrow radiation chimeras have been used as virus-infected, cyclophosphamide-suppressed recipients to analyze the major histocompatibility complex (MHC) restriction constraints on the adoptive transfer of lymphocytic choriomeningitis by immune T cells. The basic protocol employed [(A X B)F1----(A X C)F1] chimeras, where A, B, C are different MHC haplotypes, and the establishment of appropriate chimerism was measured by the capacity of, for instance, the transferred A, T cells to generate MHC-restricted, virus-specific cytotoxic T lymphocytes (CTL) in the spleen of the [(A X B)F1----(B X C)F1] recipients. The experiments show quite clearly that maximal inflammatory process is only induced when donor bone marrow, irradiated recipient and transferred T cells share at least one MHC haplotype. Compatibility of the T cells and the radiation-resistant phenotype alone in, for instance, transfer of C immune lymphocytes into [(A X B)F1----(B X C)F1] recipients produced little inflammation if the chimeras had been established for at least 10 weeks. These results are compatible with a model which proposes that the transferred T cells first replicate in MHC-compatible lymphoid tissue and are then targeted onto the appropriate MHC plus virus expressed on cells in the blood-cerebrospinal fluid (CSF) barrier. An alternative postulate, that all that is required for the development of inflammatory process is MHC-restricted T cell replication in lymphoid tissue, with subsequent nonspecific localization to the central nervous system (CNS), was explored by transferring B, immune T cells into [(A X B)F1----A] recipients. The finding was that H-2b effectors did not cause any meningitis in [H-2kXb F1----H-2k] recipients, though potent H-2b-restricted CTL were generated in the spleens of comparable chimeras. However, in the H-2k immune----[H-2kXbF1----H-2b] transfer there was evidence of moderate inflammation that was about 9 times less severe than that caused by the H-2b effectors in comparable recipients. This indicates that, for maximal inflammatory process to occur, the T cells must encounter MHC-compatible, virus-infected cells in the CNS, with the effect being absolute in one strain combination and partial in another. Possible mechanisms underlying this divergence are discussed.

Natural killer cells contribute to inflammation but do not appear to be essential for the induction of clinical lymphocytic choriomeningitis

The inflammatory exudate found in cerebrospinal fluid (CSF) of mice 6 days after intracerebral infection with lymphocytic choriomeningitis virus (LCMV) contains substantial populations of both cytotoxic T lymphocytes (CTL) and natural killer (NK) cells. Removal of NK cell activity by in vivo treatment with antibody to the asialo GM1 ganglioside and studies with NK-deficient bg/bg mice did not clearly determine whether NK cells contribute in any way to the development of clinical LCM. However, the LCM disease process induced in cyclophosphamide-suppressed, LCMV-infected recipients by the adoptive transfer of LCMV-immune spleen cells occurs in the absence of NK cell effector function in spleen, lymph nodes, or CSF of the recipients, though potent CTL populations are present in all of these sites. In this situation, NK cells are apparently not required for the induction of neurological symptoms that are indistinguishable from those of classical LCM.

Treatment of mice with polyinosinic-polycytidilic polyribonucleotide reduces T-cell involvement in a localized inflammatory response to vaccinia virus challenge

Mice inoculated intracerebrally with 10(3) PFU of vaccinia virus developed a nonfatal meningitis which was maximal 7 days after challenge. Intravenous administration of an interferon (IFN) inducer, polyinosinic-polycytidilic polyribonucleotide [poly(I)-poly(C)], on days 4 and 6 postinjection was associated with a three- to fourfold decrease in the number of T lymphocytes present in cerebrospinal fluid, reflected primarily by a decreased number of vaccinia virus-specific cytotoxic T-lymphocyte precursors. The lack of a concomitant reduction in the overall cytotoxic activity of cerebrospinal fluid cells directed against virus-infected target cells seemed to be largely due to an increase in natural killer cell activity. IFN was implicated as mediating the effect of poly(I)-poly(C) because high systemic levels of IFN were evident after injection, and neither the magnitude of the inflammatory response nor the T-cell levels were affected when poly(I)-poly(C)-treated mice were also given anti-IFN antiserum. However, the poly(I)-poly(C)-induced IFN did not seem to reduce the localized inflammatory response by affecting viral replication in brain tissue because the vaccinia virus titers present on days 6 through 8 of infection were similar to the titers in phosphate-buffered saline controls. These findings are consistent with either an effect of IFN on T-cell recruitment to the central nervous system or an inhibition of proliferation of cells participating in the response. These findings suggest that there is a potential source of complications for clinical protocols that use IFN or inducers to enhance T-cell function in various disease situations, and this effect of IFN may be a contributing factor to the immunosuppression often associated with many viral infections.

Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

The immunological surveillance hypothesis was formulated prior to the realization of the fact that an individual's effector T cells generally only see neoantigen if it is appropriately presented in the context of self MHC glycoproteins. The biological consequence of this mechanism is that T lymphocytes are focused onto modified cell-surface rather than onto free antigen. The discovery of MHC-restricted T cell recognition, and the realization that T cell-mediated immunity is of prime importance in promoting recovery from infectious processes, has thus changed the whole emphasis of the surveillance argument. Though the immunological surveillance hypothesis generated considerable discussion and many good experiments, there is no point in continuing the debate in the intellectual context that seemed reasonable in 1970. It is now much more sensible to think of "natural surveillance" and "T cell surveillance," without excluding the probability that these two systems have elements in common. We can now see that T cell surveillance probably operates well in some situations, but is quite ineffective in many others. Part of the reason for this may be that the host response selects tumor clones that are modified so as to be no longer recognized by cytotoxic T cells. The possibility that this reflects changes in MHC phenotype has been investigated, and found to be the case, for some experimental tumors. In this regard, it is worth remembering that many "mutations" in MHC genes that completely change the spectrum of T cell recognition are serologically silent. The availability of molecular probes for investigating the status of MHC genes in tumor cells, together with the capacity to develop cloned T cell lines, monoclonal antibodies to putative tumor antigens, and cell lines transfected with genes coding for these molecules, indicates how T cell surveillance may profitably be explored further in both experimental and human situations.