Effect of cytokine-induced migration of Langerhans cells on corneal allograft survival

The unique paucity of Ia+ Langerhans cells (LCs) in the central cornea contributes to the immunological privilege of corneal allografts. A variety of stimuli can induce the centripetal migration of peripheral LCs. At least one of these stimuli (i.e. latex bead instillation) induces interleukin-1 (IL-1) secretion by corneal cells which acts as a potent chemoattractant for LCs. Within 30 minutes of intracorneal injection of IL-1, centripetal migration of LCs can be detected. The presence of donor-derived LCs in corneal allografts doubles the incidence of rejection of fully allogeneic corneal allografts as well as MHC matched, multiple minor H mismatched corneal allografts. Although the presence of donor-specific LCs greatly jeopardises corneal allograft survival, migration of host-derived LCs into corneal allografts does not appear to increase the risk of rejection.

Analysis of mutational changes at the HLA locus in single human sperm

Using a simple and efficient single sperm PCR and direct sequencing method, we screened for HLA-DPB1 gene mutations that may give rise to new alleles at this highly polymorphic locus. More than 800 single sperm were studied from a heterozygous individual whose two alleles carried 16 nucleotide sequence differences clustered in six polymorphic regions. A potential microgene conversion event was detected. Unrepaired heteroduplex DNA similar to that which gives rise to postmeiotic segregation events in yeast was observed in three cases. Control experiments also revealed unusual sperm from DPB1 homozygous individuals. The data may help explain allelic diversity in the MHC and suggest that a possible source of human mosaicism may be incomplete DNA mismatch repair during gametogenesis.

The original pink-eyed dilution mutation (p) arose in Asiatic mice: implications for the H4 minor histocompatibility antigen, Myod1 regulation and the origin of inbred strains

Allelic variation of the mouse pink-eyed dilution (p) gene in common laboratory strains and wild mice was examined by Southern blot and by polymerase chain reaction. In these assays the original p mutation allele found in strains SJL/J, 129/J, B10.129(21m), P/J and FS/Ei most closely matches an Asian Mus musculus allele, confirming anecdotal accounts of the Asian origin of this mutation. In contrast, the wild-type allele found in other common laboratory strains was apparently derived from Mus domesticus. Analysis of chromosome 7 loci both proximal and distal to the p locus demonstrates that strains SJL/J, 129/J, B10.129(21M), P/J and FS/Ei contain DNA segments of varying length derived from M. musculus. Strains 129/J and B10.129(21M) contain the largest segment of M. musculus-derived DNA (about 5 cM), including the loci Myod1, p, three clustered GABAA receptor subunit loci (Gabrg3, Gabra5 and Gabrb3), and Snrpn. The difference in the species origin of genes from this region of chromosome 7 may underlie the basis of the antigenicity of the minor histocompatibility antigen H4, defined by the strain B10.129(21M), and may account for the enhanced Myod1 activity observed in SJL/J mice.

Histocompatibility differences and cardiac transplant tolerance produced by intrathymic pretreatment

Control of cardiac transplant rejection without toxic immunosuppressive drugs remains an unreached goal. Our laboratory and others have shown that intrathymic inoculation of donor-specific allogeneic spleen cells can produce tolerance to a subsequent cardiac allograft. The present experiments were designed to investigate whether the degree of donor-recipient histoincompatibility influenced the efficacy of this technique. Four congeneic strains of rats with different degrees of histoincompatibility were studied. Heterotopic cardiac transplantation was done with the following congeneic strain combinations: DA donor into PVG recipient (full major histocompatibility complex and nonmajor histocompatibility complex incompatibility); PVG.RT1a donor into PVG recipient (full major histocompatibility complex incompatibility); PVG.RT1a donor into PVG.R1 recipient (partial major histocompatibility complex incompatibility). Prospective graft recipients underwent intraperitoneal injection of 1 ml antilymphocyte serum and intrathymic injection of 5 x 10(7) prospective donor spleen cells. Three weeks later, heterotopic cardiac transplantation was done with a heart from a donor of the same strain as that used to obtain splenocytes for intrathymic injection. Prolongation of graft survival was observed in pretreated recipients in all strain combinations but was greatest in recipients that differed from donors at fewer histocompatibility loci. Complete graft tolerance was not seen in strain combinations that included nonmajor histocompatibility complex incompatibilities. DA heart survival in PVG recipients was 50.6 days (p < 0.04 versus controls); PVG.RT1a graft survival in PVG hosts was 165.8 days (p < 0.02 versus control) and in PVG.R1 recipients 163.8 days (p < 0.02 versus controls) with four of five grafts in each group surviving indefinitely (more than 200 days).

The functional basis of minor histocompatibility loci

This work addresses the functional basis of classical minor histocompatibility (H) loci. We focus on the H-3 locus, which is actually a complex genetic unit to which the phenotypic trait of tissue rejection, genes whose products stimulate specific subsets of T cells, and Ir genes have been mapped. To clarify how these genes relate to one another and to the trait of tissue rejection, strains of intra-H-3 recombinant mice were produced and analyzed. These mice allowed us to selectively elicit immune responses to Ag (referred to as type I Ag) that stimulate MHC class I-restricted CTL, or Ag (referred to as type II Ag) that stimulate MHC class II-restricted Th. The splitting of H-3 in this manner resulted in a dramatic diminution of the skin allograft response, and with rare exception, an elimination of the CTL response after spleen cell immunization. A selective response to type I Ag resulted in slow, incomplete skin allograft rejection that demonstrated both CD4+ cell-dependent and -independent components. A selective response to the type II Ag failed to result in allograft rejection. The type II Ag did, however, act as an Ir gene that determined whether responses to type I Ag could occur. Altogether, the results indicate that the trait of tissue rejection associated with H-3 is a consequence of the strongly synergistic effects of Th-CTL collaboration induced by products of type I and type II genes. Moreover, the results suggest a genetic explanation for some of the Ir gene effects associated with H-3.

A genetic analysis of human minor histocompatibility antigens demonstrates Mendelian segregation independent of HLA

An analysis of the genetic traits of human minor histocompatibility (mH) antigens is, unlike with inbred mice, rather complicated. Moreover, the fact that mH antigens are recognized in the context of MHC molecules creates an additional complication for reliable segregation analysis. To gain insight into the mode of inheritance of the mH antigens, we relied upon a series of HLA-A2-restricted cytotoxic T-cell (CTL) clones specific for four mH antigens. To perform segregation analysis independent of HLA-A2, we transfected HLA-A2-negative cells with the HLA-A2 gene: this results in the cell surface expression of the HLA-A2 gene product and, if present, mH antigen recognition. The mode of inheritance of the HLA-A2-restricted mH antigens HA-1, -2, -4, and -5 was analyzed in 25 families whose members either naturally expressed HLA-A2 or were experimentally rendered HLA-A2-positive. Analysis of distribution of the mH antigens in the parent population among the mating types, together with their inheritance patterns in the families, demonstrated that the four mH antigens behaved as Mendelian traits, whereby each can be considered a product of a gene with two alleles, one expressing and one not expressing the detected specificity. We also showed that the loci encoding the HA-1 and HA-2 antigens are not closely linked to HLA (lod scores Z (0 = 0.05) <-4.0). Some indication was obtained that the HA-4- and HA-5-encoding loci may be closely linked to HLA. While we are aware of the limited results of this nonetheless comprehensive study, we feel the similarity in immunogenetic traits between human and mouse mH antigens is at least striking.

The genetic origin of minor histocompatibility antigens

The purpose of this study was to elucidate the genetic origin of minor histocompatibility (H) antigens. Toward this end common inbred mouse strains, distinct subspecies, and species of the subgenus Mus were examined for expression of various minor H antigens. These antigens were encoded by the classical minor H loci H-3 and H-4 or by newly identified minor H antigens detected as a consequence of mutation. Both minor H antigens that stimulate MHC class I-restricted cytotoxic T cells (Tc) and antigens that stimulate MHC class II-restricted helper T cells (Th) were monitored. The results suggested that strains of distinct ancestry commonly express identical or cross-reactive antigens. Moreover, a correlation between the lack of expression of minor H antigens and ancestral heritage was observed. To address whether the antigens found on unrelated strains were allelic with the sensitizing minor H antigens or a consequence of antigen cross-reactivity, classical genetic segregation analysis was carried out. Even in distinct subspecies and species, the minor H antigens always mapped to the site of the appropriate minor H locus. Together the results suggest: 1) minor H antigen sequences are evolutionarily stable in that their pace of antigenic change is slow enough to predate subspeciation and speciation; 2) the minor H antigens originated in the inbred strains as a consequence of a rare polymorphism or loss mutation carried in a founder mouse stock that caused the mouse to perceive the wild-type protein as foreign; 3) there is a remarkable lack of antigenic cross-reactivity between the defined minor H antigens and other gene products.

Isolation of an HLA-A2.1 extracted human minor histocompatibility peptide

Purified HLA-A2.1 molecules obtained by affinity chromatography of 6 x 10(10) Epstein Barr virus (EBV)-transformed B lymphocytes were used in an attempt to isolate the human HLA-A2.1-restricted minor histocompatibility (H) peptides H-Y and HA-2. Fraction 18 of the high-performance liquid chromatography (HPLC)-separated HLA-A2.1 peptide pool was found to contain the natural HA-2 peptide. An HA-2-specific, HLA-A2.1-restricted cytotoxic T lymphocyte clone lysed HLA-A2.1+ HA-2- EBV-transformed B lymphocyte cell lines reproducibly and in a concentration-dependent fashion in the presence of fraction 18, but not in the presence of other HPLC fractions. By contrast, H-Y sensitizing activity was not found in any fraction. Amino acid sequencing of peptide fraction 18 revealed a mixture of peptides with maximal length of nine amino acids, in which the presence of Leu at positions 2 and 9 was dominant. Surprisingly, the HA-2 peptide could not be mimicked by any of the peptide mixtures synthesized according to the amino acid sequences found in fraction 18. Our failure to obtain the actual amino acid sequence of the human minor H peptide HA-2 from a peptide pool with the established pattern for binding to HLA-A2.1 may indicate that this CTL defined minor H peptide does not represent an abundant HLA-A2.1 binding peptide.

Orthotopic corneal transplantation in mice--evidence that the immunogenetic rules of rejection do not apply

The fate of orthotopic corneal transplants has been studied in inbred strains of mice. Using a surgical technique that achieves > 95% success of syngeneic cornea grafts, it was determined that a high proportion of orthotopic cornea allografts were accepted indefinitely, irrespective of the degree of immunogenetic disparity between graft donor and recipient. Grafts that succumbed to irreversible rejection developed extensive corneal edema and intrastromal neovascularization as harbingers of corneal opacity and endothelial cell failure. The highest rate of rejection occurred among grafts that confronted their hosts with multiple minor histocompatibility antigens, with or without major histocompatibility antigens. Much lower rates of rejection (< 35%) were observed when the donors of the grafts differed from recipients at class I and/or class II major histocompatibility loci. Corneal grafts that confronted their hosts with class II MHC alloantigens alone experienced early, acute inflammation, and eventually developed stomal neovascularization, but only a small minority of these grafts were eventually destroyed. Allogeneic corneas that were transplanted orthotopically into eyes of presensitized mice were uniformly subjected to an acute rejection process that produced opacity within three weeks; however, in a minority of instances, the inflammation and opacity subside, and after eight weeks the grafts displayed a clear, nonvascularized appearance. The high rate of success of even grossly histoincompatible orthotopic corneal allografts in mice resembles the extraordinary success of unmatched allogeneic corneas transplanted into human eyes. The results are discussed in terms of the possible mechanisms that permit orthotopic corneal allografts to enjoy significantly better survival than orthotopic grafts of other types of solid tissues.

Evidence that rapamycin rescue therapy delays rejection of major (MHC) plus minor (non-MHC) histoincompatible heart allografts in rats

The capacity of delayed onset of rapamycin (RAPA) therapy to block process of destruction was examined in rats undergoing heart allograft rejection. Untreated Wistar Furth (WFu; RT-1u) recipients reject Buffalo (BUF; RT-1b) heart allograft with a mean survival time (MST) of 6.5 +/- 0.5 days. A 14-day i.v.infusion of 0.8 mg/kg RAPA begun on the day of transplantation prolonged the survival to 74.1 +/- 20.2 days (P < 0.001), 0.2 mg/kg to 32.2 +/- 10.0 days (P < 0.001), and 0.08 mg/kg to 36.4 +/- 11.8 days (P < 0.001). When RAPA therapy (0.8 mg/kg) was begun 3 or 4 days after transplantation, the grafts survived 85.2 +/- 31.1 (P < 0.001), and 70.2 +/- 43.3 (P < 0.005) days, respectively. Therapy initiated on day 5 was much less effective; most transplants were rejected within 10 days; one graft survived 32 and two grafts 60 days (MST = 17.6 +/- 20.0, NS). A 0.2 mg/kg RAPA dose prolonged graft survival with initial use on days 3 (31.6 +/- 12.2 days; P < 0.001) or 4 (31.4 +/- 8.1 days; P < 0.001) but not on day 5. The 0.08 mg/kg RAPA prolonged hearts only when started on day 3 (47.2 +/- 2.7 days; P < 0.001) but not on days 4 or 5. WFu recipients treated with a subtherapeutic dose of cyclosporine (1 mg/kg; 9.1 +/- 1.5 days) displayed prolonged heart allograft function when treated subsequently with RAPA (0.8 or 0.08) beginning from days 4, 5, or 6 postgrafting. These in vivo results are supported by in vitro experiments. The frequency of BUF alloreactive elements among normal WFu LN cells (fTc) was 337 +/- 139/10(6) T cells in limiting dilution assay. Addition of RAPA (1 muMol) at the beginning of culture significantly reduced (P < 0.025) the fTc to 17 +/- 6.6/10(6), or alternatively on days 4 or 6 to 37.3 +/- 20.0/10(6) and 58.6 +/- 21.8/10(6), respectively. Thus, both in vivo and in vitro data demonstrate that delayed RAPA therapy may interrupt alloimmune reactions.

[A histo-morphometric study on peripheral nerve allografts in rats with cyclosporin A]

This investigation evaluates regeneration across peripheral nerve allografts in minor mismatch rats immunosuppressed with Cyclosporin A (CSA). Lewis(RT1(1)) rats were recipients of 20 mm sciatic nerve grafts from allogenic Fischer (RT1(1)) donors. The recipients were randomly allocated to CSA immunosuppressed or untreated groups. CSA was administered at a daily dose of 5 mg/kg by subcutaneous injection for 8 weeks. Two animals from each group were sacrificed at 2, 4, 6, 8 and 12 weeks after the operation, and bilateral sciatic nerves were resected. Until the 8th week, the CSA-treated group showed good vascularization and minimal scar formation. The regeneration was faster and better in the CSA-treated group than in the untreated group. At the 12th week, however, the CSA-treated group showed scarring in the grafted nerves and Wallerian degeneration in the distal nerves, whereas the untreated group showed increased vascularization and myelinated fibers. The results have demonstrated that CSA greatly facilitates the regeneration process across the nerve allograft whereas the discontinuation of CSA leads to reduction of the regenerated nerve fibers. These findings would indicate that the use of CSA is imperatively needed even in minor mismatch cases.

Selective breeding of miniature swine leads to an increased rate of acceptance of MHC-identical, but not of class I-disparate, renal allografts

Previous work from this laboratory demonstrated that tolerance to MHC-identical or class I-disparate renal allografts develops in approximately one third of miniature swine without exogenous immunosuppression. A back-cross study indicated that rejection of MHC-identical transplants due to minor Ag was controlled by one or possibly two non-MHC-linked, autosomal dominant Ir genes. According to this hypothesis, and assuming complete penetrance, graft acceptors would be homozygous recessive at the relevant Ir loci, as would their offspring. Alternatively, if the gene(s) were incompletely penetrant, then two acceptors could give rise to a rejector. However, a high rate of MHC-identical graft acceptance would still be expected in the offspring of acceptors even if the Ir gene(s) were incompletely penetrant. To test this hypothesis and to obtain a higher frequency of acceptor animals for studies of tolerance, a program of selective breeding of renal allograft acceptors was begun. In the present paper, we assess the effect of selective breeding on renal graft acceptance. The analysis indicates a marked increase in the rate of MHC-identical graft acceptance, from 27.3% (n = 24) for the earliest of the four chronologic subgroups assessed to 64.5% (n = 33) for the most recent subgroup (p less than 0.0001). Calculations of kinship revealed that the increased acceptance of MHC-identical grafts was not the result of differences between acceptors and rejectors in donor/recipient consanguinity. Class I-disparate grafts (n = 128) were similarly stratified chronologically and compared. Unlike MHC-identical grafts, the rate of acceptance of class I-disparate grafts has not changed over time. We conclude that rejector/acceptor status with respect to class I MHC incompatibility is determined by genetic factors in addition to those that control responses to minor antigen incompatibilities only.

Mls-1a-induced peripheral tolerance to host minor histocompatibility antigens in radiation bone marrow chimeras. Modification of T cell repertoire associated with active suppression and permanent presentation of host antigens

Minor histocompatibility Ag (mHAg) can be responsible for the development of graft vs host reaction (GVHR) after bone marrow transplantation. In a mouse model, B10.D2 donor immunization against Mls-1a prevents lethal GVHR developed by CD4+ T cells against DBA mHAg in irradiated (DBA/2 x B10.D2)F1 hosts. Such F1 hosts become 100% chimeric and show long term survival (LS mice). The cellular mechanisms underlying the tolerance in LS mice was investigated. It was found that a state of tolerance can be induced in thymectomized F1 hosts. Although spleen cells from LS mice are able to initiate lethal GVHR in third-party H-2k-incompatible hosts, no GVHR is observed in secondary hosts incompatible for specific DBA/2 mHAg. Mixed lymphocyte experiments in vitro confirm that T cells from LS mice are unresponsive toward specific DBA/2 mHAg, although they are able to proliferate in response to H-2 or Mls-1a Ag. The responsiveness to Mls-1a correlates with the presence of V beta 6+ cells in LS mice, probably derived from mature T cells present in the donor inoculum. The tolerance in LS mice is not due to the lack of DBA/2 mHAg presentation; instead, permanent presentation of Ag (Ag I and Ag II) previously described as being responsible for lethal GVHR is consistently observed. A significant protection against GVHR is obtained by transferring normal B10.D2 cells together with spleen cells from LS mice, clearly indicating the contribution of active suppression in the state of tolerance; this is further confirmed by in vitro results obtained in limiting dilution assays. It is concluded that tolerance in chimeric LS mice 1) is due to a peripheral (thymus-independent) mechanism; 2) is specific for mHAg; 3) correlates with unresponsiveness of the repertoire to host mHAg, without alteration of the repertoire for H-2 and Mls-1a Ag; and 4) is associated with an active suppression and with a permanent presentation of at least two mHAg responsible for GVHR mortality.

What are minor histocompatibility loci? A new look at an old question

In this article, Derry Roopenian relates the traditional view of minor histocompatibility (H) loci to recent advances in understanding of the tissue rejection process and the molecular nature of minor histocompatibility antigens. He proposes that minor H loci can be subdivided by the ability of their products to stimulate different T-cell subsets and discusses the implications of this concept in terms of the origins and behavior of minor H loci and their antigens, tumor immunology and autoimmunity.

Development of diabetogenic T cells from NOD/Lt marrow is blocked when an allo-H-2 haplotype is expressed on cells of hemopoietic origin, but not on thymic epithelium

Diabetes is a T cell-mediated process in NOD/Lt mice, with a major genetically recessive component of susceptibility linked to homozygous expression of the unique H-2g7 MHC haplotype. Heterozygous expression of the H-2nb1 haplotype derived from the NON/Lt strain confers diabetes resistance both in (NOD x NON)F1 hybrids and in NOD mice congenic for the H-2nb1 haplotype. However, diabetes resistance is abrogated in F1 hybrids by NOD/Lt bone marrow reconstitution. To establish whether the generation of beta cell autoreactive T cells from NOD/Lt bone marrow-derived precursors required at least heterozygous expression of the H-2g7 haplotype on thymic epithelium, adolescent thymectomized (NOD x NON)F1 mice were implanted with neonatal NON/Lt thymus grafts before lethal radiation and reconstitution with NOD/Lt bone marrow. Peripheral T cells maturing through this ectopic thymic implant exclusively expressed the NOD H-2g7 haplotype and were tolerant to H-2nb1 skin grafts. Nevertheless, diabetes developed in 32% of the NON/Lt thymus-grafted chimeras vs 38% of the sham-thymectomized NOD bone marrow chimeras. Thus, homozygous expression of the diabetes-resistant H-2nb1 haplotype on thymic epithelium failed to block development of a diabetogenic T cell repertoire. To examine if expression of H-2nb1 on hemopoietically derived APC could alter the diabetogenic potential of NOD/Lt marrow, diabetes-resistant NOD.NON-H-2nb1 congenic mice were mated with NOD/Lt mice to produce NOD-H-2g7/H-2nb1 heterozygous recipients. These were lethally irradiated and reconstituted with either NOD/Lt marrow alone, NOD.H-2nb1 homozygous congenic marrow alone, or a 1:1 mixture of the two marrow populations. By 25 wk of age, all of the MHC heterozygous recipients of NOD.NON-H-2nb1 marrow remained diabetes-free whereas 75% of the MHC heterozygous recipients of NOD/Lt marrow developed diabetes. A striking decrease in diabetes was observed when T cell precursors derived from NOD/Lt marrow interacted with H-2nb1 gene products on hemopoietically derived APC, inasmuch as only 7% of the MHC heterozygous recipients reconstituted with a 1:1 mixture of NOD/Lt and NOD.NON-H-2nb1 marrow developed diabetes. Peripheral leukocytes in all reconstitution classes expressed the MHC phenotype(s) of the marrow donor(s). Skin grafting confirmed that all reconstitution classes of MHC heterozygous recipients were tolerant to the H-2nb1 haplotype.(ABSTRACT TRUNCATED AT 400 WORDS)

Extrathymic clonal deletion of self-reactive cells in athymic mice

The repertoire of T cells present in congenitally athymic mice was studied by flow cytometric analysis on populations of T cells expanded polyclonally in vitro. Athymic (BALB/c x C57BL/6)F1 mice have levels of potentially autoreactive V beta 3- and V beta 11-bearing T cells that are significantly higher than those of euthymic CB6F1 mice. Examination of potentially autoreactive cells in athymic AKR mice, however, yielded contrasting results. V beta 6+ cells, which are deleted intrathymically in normal AKR mice, are present in the repertoire of young (less than 6-wk-old) AKR nu/nu mice. Isolation of a cloned CD4+V beta 6+ cell line with Mls-1a reactivity from young AKR nu/nu mice indicates that the correlation between TCR usage and specificity is consistent with that described in euthymic mice and that this population contains autoreactive T cells that are not anergic. By 6 mo of age, however, cells expressing V beta 6 are no longer detectable. Inability to detect these cells is not simply caused by failure to expand these cells in culture, because freshly isolated populations from old nude mice exhibit the same selective absence of V beta 6-bearing cells. The data strongly suggest that extrathymic deletion, rather than clonal anergy, accounts for the apparent absence of autoreactive V beta 6-bearing cells in aged AKR nu/nu mice.

Evidence against suppressor cell involvement in naturally acquired tolerance of a minor histocompatibility antigen

The hypothesis was investigated that suppressor cells may be responsible for maintenance of immunologic tolerance of a minor H3 antigen in mice that express the antigen naturally. Lymphoid cell populations from B6.C-H-24c (HW54) mice, a congenic-resistant strain histoincompatible with H-24b-expressing C57BL/6 (B6) mice only with respect to the H-24 locus, were examined in cell-transfer experiments to see if they contained naturally arising H-24c-specific suppressor cells. The H-24 antigen was chosen for these studies because, unlike most other minor and major histocompatibility (H) antigens, it is not detectable on mature lymphoid cells by any of several functional criteria. Thus transfer of HW54 lymphoid cells to B6 hosts could be done without the complication of inducing hyporesponsiveness de novo in the host, as occurs with other minor H antigens that are expressed on lymphocytes. B6 hosts were given HW54 skin grafts along with HW54 lymphoid cells to assess their tolerance of the H-24c-encoded antigen. The hosts were either (1) normal, nonimmune B6 mice; (2) B6 mice rendered immunodeficient by thymectomy and irradiation (TXB) and repopulated with H-24c-immune B6 lymphocytes; or (3) TXB B6 hosts repopulated with nonimmune B6 lymphocytes. In each case it was found that the additionally infused HW54 lymphoid cells did not suppress the ability of these hosts to reject HW54 skin grafts. In other words, HW54 lymphoid cells appear not to possess suppressive activity specific for the H-24c antigen that might maintain antigen-specific natural tolerance. Additional experiments were performed to determine whether HW54 lymphoid cells can inhibit the ability of sublethally irradiated B6 mice to regain the capacity to reject HW54 skin. The purpose of these experiments was to determine whether there are naturally occurring HW54 lymphoid cells that can suppress the development of lymphocytes potentially reactive to H-24c antigen that presumably emerge in B6 mice following sublethal irradiation. Such suppressor cells would be candidate initiators of self-tolerance. Here, too, no evidence for such suppressor cells was obtained.

Suppressor function of hepatic mononuclear inflammatory cells during murine chronic graft-vs-host disease. I. Macrophage-enriched cells mediate suppression in the liver

Murine chronic graft-vs-host disease (CGBHD) to minor histocompatibility antigens (B10.D2----BALB/c) is characterized by inflammatory destruction of intrahepatic bile ducts, scleroderma-like skin lesions, and lymphoid involution. Spleen cells isolated from this model proliferate poorly when stimulated with mitogens. Previous reports indicate defective lymphocyte proliferation in this model is the result of active suppression induced by the graft-vs-host reaction in the spleen and is mediated by Thy 1.2-, sIg-, plastic nonadherent, splenic natural suppressor (NS) cells. To determine whether the intense CGVHD in the liver is associated with induction of suppression, we compared the suppressor activity of hepatic and splenic mononuclear inflammatory cells isolated concurrently during murine CGVHD. Both hepatic and splenic MC suppressed the proliferation of mitogen-stimulated normal spleen cells in a non-MHC, non-Mls restricted manner. T cells contributed to the suppressor activity of both populations. However, the suppressor activity of hepatic MC was mediated largely by a macrophage-enriched population of MC while that of splenic MC was mediated largely by NS cells.

Immunodominance in the graft-vs-host disease T cell response to minor histocompatibility antigens

Immunodominance controls the generation of CTL in the C57BL/6By (B6) anti-BALB.B H-2b-matched strain combination. Despite the potential of responding to numerous individual minor histocompatibility (H) Ag on BALB.B APC, the focus of the CTL response is largely specific for only a limited number of target Ag. These minor H Ag could be distinguished by their differential expression on a panel of target cells from the CXB recombinant inbred strains, the E, G, I, J, and K (all H-2b), which express different composites of the original BALB minor H Ag. A hierarchy was observed in which first-order immunodominant Ag were present on both CXBK and CXBG cells, whereas second-order dominant Ag were found on CXBE, CXBJ, and CXBI cells. To test whether immunodominance also plays a role in the development of lethal graft-vs-host disease (GVHD) directed to multiple minor H Ag, B6 T cells were transplanted along with T cell depleted bone marrow, to irradiated (825 rad) recipients of either the BALB.B or CXB recombinant inbred strains. The results indicate that a hierarchy of immunodominance does exist in GVHD, but it differs from that predicted from the in vitro CTL studies. GVHD was observed in BALB.B, CXBE, CXBI, and CXBJ recipients, but not in CXBG and CXBK recipients. Presensitization of B6 donor mice to CXBG or CXBK splenocytes 3 wk before transplant did not significantly increase the overall GVHD potential in the corresponding CXBG or CXBK recipients. Evidence for second-order immunodominance was provided by the transfer of CXBE T cells and ATBM to irradiated CXBG and BALB.B recipients with resultant, potent GVHD.

Induction of tolerance in peripheral T cells with monoclonal antibodies

Our goal has been to develop ways to tolerize the mature immune system to any defined antigen. In this report we show that peripheral (post-thymic) T cells of mice can become tolerant to a range of antigens (human and rat immunoglobulins, and bone marrow and skin grafts that differ at multiple minor transplantation antigens). In the case of human gamma globulin (HGG), this required that the antigen be given under the cover of a short course of non-depleting anti-CD4 antibody, while for tolerance to skin and marrow grafts anti-CD8 antibody was also required. Tolerance to HGG could be reinforced by repeated injections of HGG, but was lost in the absence of any further exposure to antigen. This reversal of tolerance with time was due to new T cells being exported from the thymus, as it was not observed in tolerized, adult thymectomized mice. In contrast, tolerance to marrow and skin grafts was permanent, presumably because the established grafts acted as a continuous source of antigen to reinforce the tolerant state. Tolerance could not be broken by the infusion of unprimed spleen cells and in one example (tolerance to Mls-1a) there was clear evidence that specific peripheral T cells were anergic. We propose that anergic cells may themselves participate in reinforcing the tolerant state by competing at sites of antigen presentation.

Sequential mechanisms of cyclophosphamide-induced skin allograft tolerance including the intrathymic clonal deletion followed by late breakdown of the clonal deletion

The cellular basis of the transplantation tolerance in a model system of BALB/c (Mls-1b) mice rendered cyclophosphamide (CP)-induced tolerant to DBA/2 (Mls-1a) skin allograft was investigated by assessing V beta 6+ T cells. From our results, three major mechanisms that are essential to the CP-induced skin allograft tolerance were sequentially elucidated. The first mechanism was destruction of donor-Ag-stimulated T cells in the periphery by CP treatment. The second mechanism was intrathymic clonal deletion of donor-reactive T cells, such as V beta 6+ T cells, correlating strongly with intrathymic mixed chimerism. The clonal deletion, however, was not always essential for the maintenance of the skin allografts, because DBA/2 skin survived even after the clonal deletion terminated and V beta 6+ T cells reappeared in the periphery of the recipient BALB/c mice. The third mechanism was generation of tolerogen-specific suppressor T cells, especially in the late stage of the tolerance. In contrast, the clonal anergy that is evidenced by the specific suppression of mixed lymphocyte reaction in the recipient BALB/c mice after injecting with DBA/2 spleen cells alone was not considered as a significant mechanism in prolonging skin allograft survival because such anergic mice showed accelerated rejection of the skin allografts. These results may suggest practical hierarchy of the mechanisms of CP-induced allograft tolerance.

Bone marrow-derived cells are essential for intrathymic deletion of self-reactive T cells in both the host- and donor-derived thymocytes of fully allogeneic bone marrow chimeras

The fate of self-reactive T cells was examined in both the host- and donor-derived thymocytes of fully allogeneic bone marrow (BM) chimeras of two strain combinations of AKR/J (H-2k, IE+, Thy-1.1, Mls-1a2b) and C57BL/6 (H-2b, IE-, Thy-1.2, Mls-1b2b). Sequential appearance of host- and donor-derived T cells occurred in the thymus of both AKR----B6 and B6----AKR chimeras in which 5 x 10(6) of T cell-depleted BM cells were used to reconstitute recipients lethally irradiated with 950 rad. Thymocytes bearing V beta 6 high, which recognize MHC class II IE-binding Ag encoded by Mls-1a allele, were detected in neither host- nor donor-derived thymocytes of AKR-B6 chimeras in which Mls-1a and IE were expressed only by the BM-derived cells. Thymocytes bearing V beta 11high capable of recognizing IE were also deleted in the host- and donor-derived thymocytes of the AKR----B6 chimeras. One million of BM cells were inadequate to deletion of the B beta 6high and V beta 11high T cells in the host-derived thymocytes of these chimeras. On the other hand, significant number of V beta 6high and V beta 11high thymocytes were detected in both the host- and donor-derived thymocytes in B6----AKR chimeras where sufficient dose of IE- stem cells were used to reconstitute irradiated Mls-1aIE+ recipients. These results suggest that clonal deletion of the host- and donor-reactive T cells in both the host- and donor-derived thymocytes is an important mechanism for the induction of transplantation tolerance in allogeneic BM chimeras and that BM-derived APC may be essential for the intrathymic elimination of both the host- and donor-reactive T cells in the BM chimeras.

Resistance to H-2-restricted but not to allo-H2-specific graft and cytotoxic T lymphocyte responses in lymphoma mutant

The lymphoma mutant RMA-S escaped graft rejection after transplantation over a minor histocompatibility barrier, whereas it was rejected in H-2 allogeneic mice. The parental control line was rejected in both situations. The mutant, which had been selected against MHC class I molecules retained 5 to 10% of the wild-type H-2Db, Kb, and beta 2-microglobulin expression on the cell surface. It remained sensitive to allo-H-2b CTL in vitro, but was completely resistant to minor histocompatibility antigen-specific, H-2b-restricted CTL. It was equally resistant to other H-2b-restricted responses against internally derived Ag, such as tumor-specific CTL or a CTL clone specific for the influenza virus nucleoprotein. The results indicate a target cell defect that selectively abolishes the sensitivity to H-2-restricted CTL directed against internally processed Ag. This appears sufficient to shift the transplantation response over a minor histocompatibility Ag barrier from rejection to acceptance. There are two possible explanations for the results: 1) a block in the MHC class I-directed pathway for internal Ag processing, and 2) subthreshold H-2/Ag ligand density in relation to triggering requirements of restricted CTL. Regardless of the type of defect, the results demonstrate a difference between allo-H-2-specific and H-2-restricted CTL recognition at the level of the target cell.

A role for clonal inactivation in T cell tolerance to Mls-1a

Clonal deletion plays a major part in the maintenance of natural self-tolerance in both normal and transgenic mice. Self antigens that are expressed in the thymus result in the physical elimination of autoreactive thymocytes at a particular stage in their development. For example, the majority V beta 6- and V beta 8.1-bearing T cells that recognize the minor lymphocyte-stimulating antigen, Mls-1a (ref. 10) , are clonally deleted in the thymuses of normal mice and transgenic mice expressing Mls-1a (refs 2, 3, 9). In contrast, a very different mechanism of tolerance involving the functional inactivation, but not elimination, of autoreactive cells, termed clonal inactivation or clonal anergy, has been implicated in some experimentally manipulated systems of tolerance. To test further the mechanisms involved in self-tolerance, we have generated transgenic mice expressing a V beta 8.1 beta chain on greater than 95% of peripheral T cells and have tested tolerance to Mls-1a in these mice. Surprisingly, a significant fraction of the CD4+ peripheral cells that survived deletion were non-responsive in vitro to any stimulus tested. Naturally occurring tolerance to a self antigen expressed in the thymus can thus be mediated by clonal anergy, as well as by clonal deletion.