Weak Transplantation Antigens Research Articles

Emerging role of innate immunity in organ transplantation part III: the quest for transplant tolerance via prevention of oxidative allograft injury and its consequences

In parts I and II of this tripartite review, the innate immune system was briefly described, focusing on its emerging role in organ transplantation and by emphasizing the oxidative injury-induced allograft inflammation that promotes the generation of immunostimulatory donor- and recipient-derived dendritic cells (DCs) translating innate immune events into adaptive alloimmunity. This part III of the review discusses the possibility to induce adaptive antigen-specific T regulatory cells (Tregs) in the clinical situation by harnessing donor- and recipient-derived tolerogenic DCs (tolDCs) as inducers for alloantigen-specific adaptive Tregs, an effort that follows current trends to harnessing DCs for immunotherapy. This challenge is based on accumulating evidence from basic immunological work in support of the notion that presentation of antigens, including weak transplantation antigens under subimmunogenic conditions within a noninflammatory microenvironment, promotes generation of tolDCs. With respect to these basic immunological studies, which are expressively reviewed, prevention of oxidative allograft injury can be regarded as an efficient tool in the clinical situation to present alloantigens under subimmunogenic conditions within an intragraft noninflammatory milieu, thereby potentially generating tolDCs able to induce Tregs-mediated innate allotolerance. Various therapeutic strategies to prevent oxidative allograft injury occurring in both the brain-dead donor before/during organ removal and the recipient during/after donor organ reperfusion as well as therapeutic options to inhibit injury-induced molecular and cellular consequences are finally discussed.

Induction of long-term H-Y-specific tolerance in female mice given male lymphoid cells while transiently depleted of CD4+ or CD8+ T cells.

Rejection of H-Y-bearing primary skin grafts and generation of H-Y-specific cytolytic T cells by female mice requires the participation of both CD4+ and CD8+ T lymphocytes. Studies were conducted to investigate long-term tolerance of H-Y antigen induced in female mice by transiently depleting them of CD4+ and/or CD8+ T cells and, at the same time, giving them an injection of male lymphoid cells. We confirmed that after recovery of CD4+ to normal levels, female mice that had been transiently depleted of CD4+ cells and concurrently given an injection of male spleen cells were unable to generate H-Y-specific cytolytic T cells. Tolerance was also manifest by greatly extended survival (probably permanent in most cases) of male skin grafts. Further investigations revealed that female mice transiently depleted of CD8+ cells, and concurrently given an injection of male spleen cells, were similarly tolerant of H-Y antigen later when numbers of CD8+ T cells returned to normal. Moreover, small numbers of male cells were detectable in spleen and lymph nodes of tolerant females long after they had been given an injection of male cells and depleted of either CD4+ or CD8+ T cells, whereas no male cells were detected in (nontolerant) females given male cells and control antibodies. These findings show that tolerance of the relatively weak transplantation antigen, H-Y, can be achieved simply by giving male antigen-bearing spleen cells to the host while it is transiently depleted of a type of cell it needs in order to reject those cells, thus allowing the male cells to persist in the host. Furthermore, depletion of helper cells is not obligatory to achieve tolerance. It has been hypothesized that tolerance of H-Y antigen in females given male lymphoid cells while temporarily depleted of CD4+ lymphocytes results from unresponsiveness (anergy) induced in H-Y-specific CD8+ cells that are exposed to H-Y antigen in the absence of help from CD4+ cells. Interpretations of our findings are discussed in relation to this hypothesis.

Expression and function of Qa-2 major histocompatibility complex class I molecules in transgenic mice

Qa-2 molecules are weak transplantation antigens encoded by class I genes of the major histocompatibility complex. When expressed in transgenic CBA mice, Qa-2 molecules provoke rapid rejection of skin grafts and strong, Qa-2 specific, cytotoxic T-cell responses. Efficient rejection of skin grafts from Qa-2 transgenic mice takes place when Qa-2 molecules are attached to the cell membrane with a glycophosphatidyl anchor or by a transmembrane protein domain, except that rejection times are slightly longer in the former case. These results demonstrate that Qa-2 molecules can behave as major transplantation antigens, as do closely related H-2 molecules. Failure of Qa-2 molecules to provoke strong T-cell responses in non-transgenic mice is probably due to the very low level of expression of Qa-2 molecules in skin keratinocytes from such mice since these cells express increased levels of Qa-2 molecules in all Qa-2 transgenic mice.

Elicitation of weak immune response in larval and adult Xenopus laevis by allografted pituitary.

To test the claim that tolerance to organ-specific self antigens is established during the ontogenic development of the immune system, pituitary anlagen were removed from early tailbud embryos of Xenopus laevis, and the resulting hypophysectomized tadpoles were grafted with pituitaries after the tadpoles had become immunocompetent. The result was that none of the histocompatible or allogeneic pituitary grafts was rejected throughout an observation period of 100 days. Subsequent experiments revealed that hypophysectomy does not affect the development of immune responsiveness. In addition, allogeneic pituitary grafts were usually not rejected by unoperated, normal tadpoles or froglets, although they suffered lymphoid invasion to various degrees. However, a significant number of allogeneic pituitaries was rejected when they were grafted, either after or at the same time as the grafting of skin from the pituitary donors. We conclude that the pituitary of Xenopus possesses weak transplantation antigens or expresses them in ways that make them less accessible to the immune surveillance system of the allogeneic host.

Review lecture. Immunology of H-Y antigen and its role in sex determination.

H-Y was originally discovered as a transplantation antigen that caused female mice of certain inbred strains to reject skin from otherwise identical males. The ability to make the skin graft rejection response and, in vitro, cytotoxic T cell responses against H-Y is controlled by genes within the major histocompatibility complex, H-2, and by non-H-2 genes. H-Y belongs to a class of weak transplantation antigens characterized by an inability to elicit responses under many conditions. Although genetic factors are very important in determining responsiveness, their action can be modified by immunization procedures. H-Y has been proposed as the differentiation signal that causes the formation of the testes from the undifferentiated gonad in the developing embryo. This hypothesis has been explored by using a series of mice whose karyotype and phenotypic sex are paradoxical.

A new H-2-linked class I gene whose expression depends on a maternally inherited factor.

The maternally transmitted antigen (Mta) is expressed on the cells of most strains of mice. It is a medial histocompatibility antigen, that is, it is recognized by unrestricted cytotoxic T lymphocytes as are major H antigens, but unlike these it is a weak transplantation antigen and does not itself restrict the T-cell recognition of minor H antigens. All other medial H antigens are encoded by genes closely linked to the major histocompatibility complex, H-2 in the mouse. By contrast, Mta appeared to follow extrachromosomal, maternal inheritance. Several substrains of NZB, NZO and non-inbred European NMRI mice are Mta-negative. Females of these strains bear only Mta- offspring, while females of the inbred Mta+ strains bear only Mta+ offspring. Repeated backcrossing from Mta+ females to NZB or NMRI males has shown that, given the right cytoplasmic genes, the chromosomal genes of these Mta- strains permit expression of Mta2. As the Mta type of a mouse cannot be influenced by embryo transfer or foster nursing, we concluded that it was determined by a cytoplasmic factor (Mtf), transmitted through the egg. We now show that a gene, Hmt, closely linked to the H-2 complex, is also required for expression of Mta.

Ontogeny of Transplantation Immunity in the Common Frog, Rana temporaria L.

Viability of allografts exchanged between the field-collected individuals of the common frog, R. temporaria, was long in tadpoles grafted during and immediately after closing of operculum; median survival time (MST) was 26 and 18 days, respectively. This probably reflected the immaturity of the host immune system and temporary tolerance to weak transplantation antigens. Allograft viability was the shortest in tadpoles grafted at foot-paddle stage (MST, 11 days). It was independent from the origin and size of the grafts. Such rate of rejection might reflect a maximal immunological potential of the host and the absence of any suppressor factors in response to highly polymorphic frog transplantation antigens. A gradual prolongation of allograft viability was observed in animals grafted at final stages of metamorphosis, in froglets, and in sexually mature adults (MST: 13, 17, and 28 days, respectively). In particular age groups viability of allografts from sibling donors was longer and from nonsibling ones shorter than MST values cited above. Immunological memory of transplantation antigens did not disappear during the host metamorphosis, as MST (10 days) of second-set allografts in metamorphosing hosts sensitized during larval life was considerably shorter than the viability of the sensitizing grafts in the same age group. The ontogeny of the response to alloantigens reflecting the immunological potential and the appearance of self-tolerance can be realized in different ways, depending on a particular amphibian species.

The H-Y antigen and its role in natural transplantation.

A concise overview of the transplantation biology of the H-Y antigen is presented with particular reference to: its prototypic behavior as a weak transplantation antigen; the facility with which mice of certain inbred strains can be rendered tolerant of H-Y incompatible skin grafts; its capacity to instigate graft-versus-host reactions; its significance in clinical transplantation; and finally, H-2 control of anti-H-Y immune responses. The role of the H-Y antigen in natural transplantation, i.e. pregnancy, is then reviewed. Evidence is presented to support the hypothesis that in certain cases maternal immune responses directed specifically to the H-Y antigen can exert selective pressures on male zygotes, producing deviant sex ratios in certain experimental and clinical situations.

Immunogenic properties of hamster tumours of herpesvirus hominis aetiology

Cells derived from HSV-induced tumour lines were attenuated by X-irradiation (15,000 rads) and used to immunize groups of hamsters prior to challenge with homologous tumour cells. The results indicate that the three HSV tumours studied possess a weak transplantation antigen(s). Some cross-immunity between these tumours was observed, although the rejection antigen(s) were distinct from those of a SV40-induced hamster tumour line.

On the genetics of transplantation in the lizardCnemidophorus tigris

A total of 195 allografts were analyzed among 14 wild individuals of the whiptail lizardCnemidophorus tigris. The cumulative time for rejection of all allografts by each individual varied in a uniformly graded sequence ranging from 502 to 2263 days. One individual did not reject 9 of 13 allografts. A comparison of rejection rates revealed that the relative degree of antigenicity of a donor was more or less proportional to its immune response, i. e., the strongest rejectors tending to elicit the strongest immune response and the weakest rejectors the weakest response. Such a relationship as well as the graded sequence of rejection suggest that neither the “many weak transplantation antigen” hypothesis, nor the “strong locus” hypothesis adequately explain the present results. Probable genetic models are discussed and a summary of transplantation studies in lower vertebrates is presented.

A RAPID METHOD FOR PREIMMUNISATION AND GRAFTING OF MICE WITH EAR SKIN

A schedule for a histocompatibility test among mice involving preimmunisation with ear skin is described and has been tested with the weak transplantation antigen H-Y in C57BL responder and C3H nonresponder strains. The transplantation technique was tested by autografting, and more than 99% of the operations were successful. The priming method reduces the survival of ear skin grafts in every combination tested.

Further characterization of immunological unresponsiveness induced in mice by ultraviolet radiation. Growth and induction of nonultraviolet-induced tumors in ultraviolet-irradiated mice.

Ultraviolet (UV)-irradiated mice were compared with unirradiated mice for their susceptibility to primary and transplanted tumors etiologically unrelated to UV radiation. Although UV-irradiated mice are unable to reject transplants of highly antigenic syngeneic tumors induced by UV light, the growth of syngeneic, non-UV-induced tumors generally was not accelerated in these animals. Furthermore, UV-irradiated mice were no more susceptible to the induction of primary leukemias, mammary tumors, or sarcomas than were unirradiated animals. Tests of immune responses to weak transplantation antigens showed that UV-irradiated mice rejected H-Y-incompatible skin grafts as vigorously as did normal animals, and that the primary in vitro cytotoxic responses of spleen cells from UV-irradiated mice to trinitrophenyl (TNP)-modified syngeneic cells and to Hh antigens were unaffected. We conclude that the susceptibility of UV-irradiated mice to challenge with UV-induced tumors represents a selective unresponsiveness, and that it is not attributable to a generalized deficiency in the immune response to tumor-specific antigens or to weak transplantation antigens.

Immunologic reactivity to weak transplantation antigens: factors which favor sensitization rather than tolerance.

Immunologic reactivity to weak transplantation antigens: factors which favor sensitization rather than tolerance.

Inhibition of erythropoiesis in the spleens of irradiated mice injected with allogeneic lymphocytes: Reactivity of lymphocytes against non-H-2 transplantation antigens

Abstract A sensitive technique has been applied for studying the graft-vs-host reactivity of murine lymphocytes against non-H-2 transplantation antigens. The method is based on the finding that allogeneic lymphoid cells are able to depress the growth of erythroid cells in the spleens of lethally irradiated mice injected with syngeneic bone marrow cells. Using this technique, it was possible to show that large numbers of normal, non-sensitized lymphocytes can depress the hematopoietic activity of bone marrow cells with different non-H-2 antigens. This effect was markedly enhanced by prior sensitization of the cells in the spleens of X-irradiated recipients having the same genotoype as the target bone marrow cells. Such sensitized cells did not exhibit any detectable reactivity against bone marrow cells having completely different transplantation antigens. They also exhibited an impaired capacity to react against bone marrow cells bearing both foreign H-2 antigens and the non-H-2 antigens against which the cells had been sensitized. Lymphoid cells which were recovered from the spleens of irradiated mice differing at both H-2 and non-H-2 transplantation antigens exhibited a strong reactivity against the foreign H-2 antigens but largely lacked reactivity against the non-H-2 antigens. The results emphasize that the present technique is useful for studies on the graft-versus-host reactivity of lymphocytes against weak transplantation antigens.

The effect of X-ray on the antigenicity of donor cells in transplantation immunity

Summary The x-ray sensitivity of normal histocompatibility antigens in mice was studied. Strong antigens associated with the H-2 locus were found to be resistant to as much as 12,800 r in vitro , in that mice inoculated with such heavily irradiated cells were immunized by them and gave second set responses to subsequent skin grafts. Weak antigens associated with H-1 and H-3 loci were effectively destroyed by as little as 400 r, failing to induce immunity after irradiation in vitro . The cells used to induce immunity were spleen cells and a methylcholanthrene-induced sarcoma. Possible biologic relationships between strong and weak transplantation antigens are discussed and a reason for their different sensitivities to irradiation suggested.

The Effect of X-Ray on the Antigenicity of Donor Cells in Transplantation Immunity

Summary The x-ray sensitivity of normal histocompatibility antigens in mice was studied. Strong antigens associated with the H-2 locus were found to be resistant to as much as 12,800 r in vitro, in that mice inoculated with such heavily irradiated cells were immunized by them and gave second set responses to subsequent skin grafts. Weak antigens associated with H-1 and H-3 loci were effectively destroyed by as little as 400 r, failing to induce immunity after irradiation in vitro. The cells used to induce immunity were spleen cells and a methylcholanthrene-induced sarcoma. Possible biologic relationships between strong and weak transplantation antigens are discussed and a reason for their different sensitivities to irradiation suggested.