Induction of unresponsiveness to Heymann's nephritis: inhibited by monoclonal antibody to CD4 but not to CD8

The cellular basis of cardiac allograft rejection. IX. Ratio of naïve CD4+CD25+ T cells/CD4+CD25− T cells determines rejection or tolerance

Naïve CD4+ T cells are central to allograft rejection, but include 3-10% CD4+CD25+ T cells that induce and maintain immune tolerance. Whether increasing the ratio of CD4+CD25+ T cells can inhibit rejection and induce tolerance is not known. This study examined the effects that naïve CD4+CD25+ and CD4+CD25- T cells have on rejection of MHC incompatible PVG cardiac allografts in whole body irradiated DA rats. The ratio of CD4+CD25+ T cells to CD4+CD25- T cells was increased to examine if this delayed rejection. CD4+CD25- T cells alone restored near first set rejection time of 8-10 days and were significantly faster than unfractionated CD4+ T cells which nearly always took over 10 days to effect rejection. Enriched CD4+CD25+ T cells, either fresh or cultured with IL-2 and donor alloantigen, did not restore rejection. Admixing naïve CD4+CD25+ T cells with CD4+ T cells at a ratio of 1:10 prevented graft destruction by rejection. Naïve CD4+CD25+ T cells, either fresh or cultured with IL-2 and donor alloantigen, at a ratio of 1:1, prevented significant episodes of rejection and grafts survived >300 days. These grafts had large areas of normal myocardium but had some foci of CD4+, CD8+ and CD25+ cellular infiltration. This study found CD4+CD25- T cells were the principal mediators of rejection and naïve CD4+CD25+ T cells partially inhibited the CD4+CD25- T cells in unfractionated CD4+ T cells. Increasing the ratio of naïve CD4+CD25+ to CD4+CD25- T cells inhibited rejection allowing grafts to survive indefinitely and may induce transplant tolerance, without a need for long-term immunosuppression.

Anti-CD4 Monoclonal Antibody-Induced Tolerance to MHC-Incompatible Cardiac Allografts Maintained by CD4+ Suppressor T Cells That Are Not Dependent upon IL-4

Anti-CD4 mAb-induced tolerance to transplanted tissues has been proposed as due to down-regulation of Th1 cells by preferential induction of Th2 cytokines, especially IL-4. This study examined the role of CD4+ cells and cytokines in tolerance to fully allogeneic PVG strain heterotopic cardiac allografts induced in naive DA rats by treatment with MRC Ox38, a nondepleting anti-CD4 mAb. All grafts survived >100 days but had a minor mononuclear cell infiltrate that increased mRNA for the Th1 cytokines IL-2, IFN-γ, and TNF-β, but not for Th2 cytokines IL-4 and IL-6 or the cytolytic molecules perforin and granzyme A. These hosts accepted PVG skin grafts but rejected third-party grafts, which were not blocked by anti-IL-4 mAb. Cells from these tolerant hosts proliferated in MLC and produced IL-2, IFN-γ, and IL-4 at levels equivalent to naive cells. Unfractionated and CD4+ T cells, but not CD8+ T cells, transferred specific tolerance to irradiated heart grafted hosts and inhibited reconstitution of rejection by cotransferred naive cells. This transfer of tolerance was associated with normal induction of IL-2 and delayed induction of IFN-γ, but not with increased IL-4 or IL-10 mRNA. Transfer of tolerance was also not inhibited by anti-IL-4 mAb. This study demonstrated that tolerance induced by a nondepleting anti-CD4 mAb is maintained by a CD4+ suppressor T cell that is not associated with preferential induction of Th2 cytokines or the need for IL-4; nor is it associated with an inability to induce Th1 cytokines or anergy.

Active Heymann nephritis in complement component C6 deficient rats

The mechanisms of renal injury that result in proteinuria in active Heymann nephritis (AHN) remain unclear, though data suggest that in analogy of the passive form of the disease the membrane attack complex C5b-9 may be involved. AHN was induced in an inbred strain of PVG/c-rats that are totally deficient in the C6 component of complement and are unable to form the lytic C5b-9 complex, as well as in non-complement deficient PVG/c+ rats that are immunologic identical to the deficient strain. In both groups of animals comparably high titers of anti-Fx1A autoantibodies were found after three weeks and persisted at 40 weeks. Proteinuria was also similar in both groups, and was first evident at six weeks. High levels of urinary protein, ranging from 200 mg/24 hr to 500 mg/24 hr, were found after 10 weeks and persisted up to one year. Renal biopsy findings at various times post-immunization were identical in both groups, including immunofluorescence staining for Ig and C3 deposits, and also EM findings of subepithelial electron-dense deposits were not different. The injection of heterologous rabbit complement, that partially and temporarily restored the CH50 activity in PVG/c- rats did not alter or hasten the disease. Long-term follow-up showed that all rats in both groups continued to have severe proteinuria and that most animals died between 8 to 12 months after disease induction, without renal impairment. EM findings in serial biopsies demonstrated that the growth of the subepithelial deposits as measured by surface area occurred between weeks 4 and 12. A positive correlation (r = 0.94) between the size of the deposits and the level of proteinuria was found. These studies demonstrate that the membrane attack complex of complement does not play a major role in AHN. The relationship of the size of the immune deposits to the level of proteinuria suggests that the growth of the immune deposits on itself initiate secondary mechanisms that damage the permselective characteristics of the glomerular membrane.

Hereditary C6 deficiency in a strain of PVG/c rats

A chance observation has led to the discovery of a strain of PVG rats (PVG/c-) which are deficient in complement (C) component C6. Analysis of total haemolytic activity (CH50) of PVG/c- serum revealed an absent CH50 activity compared with serum of other rat strains and of a PVG/c rat (PVG/c+) that showed normal C activity. Thus, the PVG/c- rat was unable to activate the C5b-9 membrane attack complex. To gain insight into the complement abnormalities, analysis of individual C components was performed. Testing the PVG/c- serum in a C6 haemolytic assay and using deficient human sera showed a deficiency of C6 in the PVG/c- rat. Highly purified human C6 and human sera deficient in other components were able to reconstitute the CH50 activity of the PVG/c- rat. The possibility that an inactivator of C was present in PVG/c- serum was excluded. The deficiency was found to be inheritable and under the control of an autosomal recessive gene. Furthermore, tissue antigens and immunity of the PVG/c- rat were found to be identical to those determined in the PVG/c+ rat. With regard to their health status, the PVG/c- animals seem to have no disadvantages compared with PVG/c+ rats when held under the same conditions within the protected environment of animal facilities. Taken together, both rat strains provide an unique animal model for studying the biological role of C, particularly the C5b-9 membrane attack complex in experimental medicine.

Partial prevention of active Heymann nephritis by 1 alpha, 25 dihydroxyvitamin D3

The hormone 1 alpha, 25 dihydroxyvitamin D3 (1,25(OH)2D3) has potent immunosuppressive effects in vitro. Recent publications also described a protective effect of the hormone in various animal models of immune-mediated diseases. To test its in vivo activity we induced active Heymann nephritis in Lewis rats that were either untreated or treated with 1,25(OH)2D3 or its synthetic 20-epi analogue, KH1060. Treatment with cyclosporine A (CsA) was used as an immunosuppressive control. In this nephrotic model the administration of 1,25(OH)2D3 (0.5 microgram/kg body weight) given on alternate days during the first 13 days after active immunization significantly reduced the proteinuria as measured by weeks 7-9. This reduction was comparable to the reduction observed in rats treated with CsA (20 mg/kg) on alternate days. A second series of experiments with 1,25(OH)2D3 confirmed these findings. The level of autoantibodies was found to be significantly suppressed during the treatment time in the CsA (20 mg/kg) group, whereas the limit of significance (P = 0.06) was reached in the 1,25(OH)2D3 (0.5 microgram/kg) group. The size of the immune deposits also was found to be substantially smaller in the groups that developed less proteinuria. The administration of 1,25(OH)2D3 transiently increased the mean serum calcium concentration with 2.5 mg/dl above the pretreatment values, and the urinary calcium excretion by a factor of 3-5 during the short treatment time. Treatment with the analogue KH1060 did not reduce the proteinuria significantly. Our experiments add evidence to the hypothesis that 1,25(OH)2D3 in pharmacological doses has immunosuppressive potency.

Presence of CD4+ T suppressor cells in mice rendered unresponsive to tumor antigens by intravenous injection of irradiated tumor cells

We used in vivo and in vitro assays to determine whether suppressor cells are generated in mice rendered unresponsive to tumor-specific antigens by intravenous (i.v.) injection of non-replicating tumor cells. The results show that a single i.v. injection of 2 x 10(7) irradiated P815 tumor cells resulted in the induction of a state of specific unresponsiveness to tumor-associated antigens, as revealed by the inability of the treated mice to achieve immunologically-mediated regression of an intradermal P815 tumor containing C. parvum, or to generate effector T cells capable of causing rejection of a P815 tumor in T-cell-deficient (T x B) test recipients. Failure to respond to tumor antigens was associated with the presence in spleen of CD4+ T cells capable, on passive transfer, of suppressing adoptive T-cell-mediated tumor regression in T x B recipients. However, the same CD4+ suppressor cells failed to inhibit the generation of tumor-specific cytotoxic T lymphocytes (CTL) in vitro. On the contrary, spleen cells from mice made unresponsive by i.v. injection of tumor cells were primed to generate CTL in response to tumor antigens in vitro. Taken together, our results suggest that unresponsiveness induced by i.v. injection of tumor antigens is an active process mediated, at least in part, by CD4+ T suppressor cells, and that these cells coexist in the spleen with antigen-primed effector T cells with a capacity to generate tumor-specific CTL when released from suppression in vitro.