Attempts to demonstrate an in vivo role for serum blocking factors in tolerant mice

Constitutive synthesis of tumor necrosis factor in the thymus

Although tumor necrosis factor (TNF) is a major mediator of endotoxic shock, the normal function of TNF that has preserved this protein throughout mammalian evolution remains unknown. If the protein serves a role in normal development or homeostasis, it must be produced under physiologic conditions. To determine whether TNF secretion occurs in normal animals, and to define the tissue sources of the protein, we prepared a reporter construct in which the TNF coding sequence and introns are replaced by the chloramphenicol acetyltransferase (CAT) coding sequence. This construct was inserted into the murine genome, yielding 13 transgenic founders. Macrophages harvested from 4 of the transgenic lines expressed CAT activity after stimulation with Escherichia coli lipopolysaccharide in vitro. Each of these 4 transgenic lines also constitutively expressed CAT activity in the thymus but in no other tissue examined. Cultured thymocytes secrete TNF, as demonstrated both by cytotoxicity assays and by immunoprecipitation of radiolabeled thymic culture medium. CAT activity was associated with the thymic lymphocyte population and not with thymic macrophages or dendritic cells. CAT activity was present in thymic lymphocytes irrespective of CD4 or CD8 expression; T cells from the spleen, however, had no detectable CAT activity. The biosynthesis of TNF in the thymus of normal animals implies a role for this protein in the development or regulation of the immune response.

[The allogeneic liver transplantation. II. Immunological examinations in pigs (author's transl)]

Although pig liver allograft induces a regular cellular immune response the transplanted live shows only mild injection or can be accepted. Long term survivors show a reduced cellular immunity in vitro involving the lack of donor-specific memory cells and the development of blocking antibodies. These immunoglobins are mainly considered to mediate the increased survival time of the grafted liver. They show anti-Ia-like specificities and their induction is favoured by the particular Ia- and SD-antigen pattern of the liver tissue. The immunological status observed in liver-allografted pigs is comparable to the active enhancement. In terms of morphological, functional and immunological changes the clinical liver transplantation shows striking similarities to the experimental animal model with pigs. The predominant, non-immunological complications could be overcome in the past few years so that the one-year survival rate was increased to 50%. The good survival rate and the low rejection risk due to the immunological peculiarity of the liver seem to justify the clinical application of the liver transplantation in cases of severe liver disorders which cannot be treated by conventional clinical methods.

Functional clonal deletion in immunological tolerance to major histocompatibility complex antigens

CBA (H-2k) mice were rendered tolerant to H-2d antigens by injection of (CBA X BALB/c)F1 spleen cells at birth. At intervals of 2 days to 12 weeks, the frequencies of anti-H-2d cytotoxic T lymphocyte precursor cells (CTL-P) in thymus and spleen were determined by using a limiting-dilution microculture assay system for CTL-P. This assay, utilizing irradiated H-2d stimulator cells and concanavalin A-induced spleen cell conditioned medium, was shown to be linear over the range 30 to 100,000 responder cells and uninfluenced by IJ-positive cells. A profound and long-lasting deficit in activatable CTL-P, first demonstrable by day 5 of life in the thymus and day 8-10 in the spleen, developed in mice rendered tolerant, reaching a greater than 95% reduction by 6 weeks. Functional clonal deletion thus seems to be at least as important in the tolerant state as suppressor T cells. Repeated in vivo administration of anti-IJk serum partially inhibited clonal deletion, suggesting either that suppressor T cells are actively involved in producing clonal deletion or that IJk-bearing cells in the donor inoculum or the host represent an important factor.

Studies on transplantation immunity. IV. Murine natural immunity to lymphoid cells in vivo

A natural response acting to discriminate between allogeneic and syngeneic lymphocytes in vivo is described for normal mice. Eighteen to 24 h after systemic injections of low doses of 51Cr-labeled cells, less radioactivity is found in the lymph nodes after allogeneic transfer. The spleen but not the liver participates in the response. It can be abolished by neonatal induction of transplantation tolerance, is shown to be immunologically specific, and is resistant to irradiation up to 1000 rd, although a radiosensitive phase occurs during recovery from sublethal irradiation. The response is cell-mediated but depends upon cooperation from a factor present in normal serum. It is thymus-independent: this clearly distinguishes it from the superficially similar immune response acquired by immunization and aligns it with the class of responses to which the hybrid histocompatibility response and natural killer-like phenomena belong. Unlike these, however, it is present at birth and directed primarily against H-2 antigens. It appears to follow the classical transplantation rules in a limited range of strains. Some of the difficulties inherent in this type of study are discussed.

Antagonistic maternal immune reactions (rejection and facilitation) to the embryo in the urodele amphibian Salamandra salamandra lin

In vitro assays have been employed to demonstrate that pregnant salamanders mount an immune reaction against their embryos. Maternal spleen cells kill up to 85% of dissociated embryonic epidermal cells during a 48 h incubation period. The degree of killing depends upon the ratio of maternal to embryonic cells and on the number of embryos borne by the mother. The cytotoxicity shows considerable specificity for the embryos of a given mother although a weak degree of killing can occur with embryos from other mothers, presumably due to some form of cross-reactivity. The effect is inhibited by the addition of maternal serum to the cultures. The degree of protection is also a function of the number of embryos borne by the mother. Pre-incubation experiments indicate that the maternal serum has a protective action on the embryonic cells which is largely specific for the female's own embryos (and suggested to be antibody in nature) and an inhibitory action on the maternal spleen cells which occurs also with spleen cells of other females (and suggested to be either an immune complex or a nonimmunological substances). An increase in beta protein peaks is seen following electrophoresis of sera from pregnant (and also allografted) salamanders. These findings indicate that the pregnant salamander mounts a double immune reaction against her embryos, an aggressive (rejection) reaction and a protective (facilitation) reaction.

Analysis of mechanisms of maintenance of neonatally induced tolerance to foreign alloantigens

Mice made tolerant to allogeneic tissues in neonatal life have been examined at different times for their ability to respond to the tolerizing determinants in a variety of assays (in vitro CML, MCL and in vivo GvH assays). All animals were tolerant in terms of their inability to produce CTL to the relevant determinants, and to induce GvH in lethally irradiated F1 recipients. Nevertheless, some mice also showed a normal MLC proliferative response and contained antigen-specific serum inhibitory factors, while other mice contained apparently antigen-specific suppressor cells. The pool of the latter, futhermore, was expanded considerably upon adoptive transfer of tolerant cells (with tolerizing antigens) to lethally irradiated syngeneic recipients. The data are compatible with the notion that suppression of clonal expansion represents the primary mechanism of tolerance maintenance (induction), and that the infrequently observed serum reactivity in such tolerant mice represents a vestige of the means whereby-cell mediated suppression was induced.

A solution to the graft-versus-host problem in bone marrow transplantation to humans

Many clinical situations arise where it would be desirable to transplant bone marrow to a marrow function deficient patient. However, bone marrow is immunologically competent by virtue of its content of lymphocyte precursors. Marrow transplantation in these patients is followed by the graft's immunological rejection of the patient - a fatal disease. A system for specific abrogation of this graft-versus-host disease after xenogeneic bone marrow transplantation to humans is presented. In this system, prospective patient cells are removed by skin biopsy for example, and injected into a fetal chimpanzee. The fetal chimpanzee becomes tolerant to this patient's antigens and will not attack or reject them when its bone marrow is removed after birth and injected into the specific patient from whom the tolerogenic cells were obtained. A simple and straightforward experimental test of this system's clinical applicability is also presented.

Lymphocytes which differentiate in an allogeneic thymus. II. Evidence for both central and peripheral mechanisms in tolerance to donor strain tissues

Nude mice which have been grafted with an allogeneic H-2-incompatible thymus are frequently specifically tolerant to skin grafts from the thymus donor strain. The evidence presented here indicates that both clonal deletion and peripheral suppressor cells play a part in maintaining this tolerance.

Persisting T cells in rats tolerant of human serum albumin. The significance of tolerant and nonimmune T cells which preferentially restrict high affinity antibody synthesis

The adoptive response of primed rat thoracic duct lymphocytes ('TDL) following specific antigen challenge (soluble human serum albumin, s-HSA) was restricted when cells were transferred into syngeneic, adult (AS2 X AS)F1 hybrid recipients in comparison with irradiated hosts. This adoptive memory response was also inhibited in irradiated recipients by transferring nonimmune TDL along with 'TDL. Recirculating B cells (B-TDL) did not inhibit the 'TDL response, indicating that the adoptive secondary response was regulated by T cells. Antibody synthesis was preferentially restricted in the high affinity memory cell precursor population, demonstrating a role for T cells in regulating the maturation of antibody affinity. The adoptive memory response was liberated from this T regulatory effect in adult recipients when hosts were challenged with the alum-precipitated adjuvant form (HSA-adj) rather than the soluble form of HSA. Since the adoptive memory response was sensitive to the presence or absence of T cells, this experimental model was used to determine whether or not T cells were eliminated from HSA-tolerant rats. Antibody synthesis by 'TDL was reduced approximately 10-fold compared with controls when transferred into tolerant recipients and challenged with either s-HSA or HSA-adj; a similar reduction was not observed by substituting bovine serum albumin (BSA) 'TDL and challenging with s-BSA. The tolerance-induced inhibition of HSA 'TDL was destroyed by irradiation and TDL from HSA-tolerant donors were more effective than normal nonimmune TDL in reducing the adoptive HSA 'TDL response. HSA-tolerant TDL did not inhibit the BSA 'TDL response significantly. The results indicate that T cells are not eliminated by tolerance induction in this model and after interaction with tolerogen may exert an active (or competitive) role in restricting antibody synthesis by high affinity B memory cell precursors. However, the fact that tolerant T cells are not able to prevent a primary response suggests that unresponsiveness to HSA in the T compartment represents a functional deficiency and not an active suppression at this level. Nevertheless, the presence of these tolerant cells probably accounts for the failure of antibody affinity to mature in partially tolerant rats.

Maternal immunocompetence. I. The graft-versus-host reactivity of lymphocytes from pregnant rats and the distribution pattern of 51Cr-labeled lymphocytes in pregnant mice

Lymphocytes from the peripheral blood, spleen, or para-aortic lymph nodes of prrimigravida L rats carrying (L X BN) F1 (LBN) fetuses are fully capable of mounting graft-versus-host (GVH) reactions in LBN F1 recipients. The reactivity of lymphocytes from interstrain pregnant (L X BN) or intrastrain pregnant (L X L) rats, or from rats postpartum from these pregnancies, is equivalent to that of normal virgin females over a full dose-response curve, ruling out both specific and nonspecific effects of pregnancy on the intrinsic GVH competence of the maternal thymus-derived (T) lymphocyte. Attempts to block GVH reactivity with serum from pregnant rats were unsuccessful. In addition, when the distribution pattern of 51Cr-labeled syngeneic and semiallogeneic lymphocytes was studied in intact primigravida mice, there was no difference between interstrain and intrastrain pregnant mice, and there was no evidence of immunologically specific 'trapping' in the para-aortic lymph nodes draining the interstrain pregnant uterus.

Neonatally induced transplantation tolerance: in vitro evidence supporting a clonal inactivation mechanism

Mixed lymphocyte culture (MLC) tests on the cells of mice made fully tolerant to allogeneic tissues in neonatal life showed an absence of specific antigen-reactive cells. Similary, no cells cytotoxic in a chromium release test could be detected. The absence of reactivity in the tolerant populations could not be accounted for by either suppressor cell activity or serum blocking factors. By contrast, mice in which partial tolerance had been deliberately or inadvertently induced often possessed detectable numbers of MLC-reactive cells and, after grafting, their sera inhibited the MLC reactivity of normal cells. These results are discussed in terms of possible mechanisms of self tolerance.

Histocompatibility studies in a closely bred colony of dogs. V. Mechanisms of cellular adaptation in long-term DL-A identical radiation chimeras

20 Cooperstown beagles of known DL-A genotypes (B" dogs) were exposed to supralethal total body irradiation and received a bone marrow allograft from a DL-A identical donor (A" dog); the resulting chimeras have survived uneventfully for 882, 1466 days, with no evidence of secondary disease, and have been tolerant to kidney and skin allografts obtained from the donor of marrow. Treatment of "A" dogs with serum obtained from their long-term "B" chimeras had no significant effect upon the ability of the recipients to reject "B" skin allografts...

Neonatal tolerance induced by antibody against antigen-specific receptor

Specific immunologic unresponsiveness is induced by injecting adult or neonatal mice with antibody against antigen-specific receptor (antireceptor antibody). Suppression in mice treated as adults lasts several weeks, and cells from these suppressed mice respond normally in culture. In contrast, unresponsiveness induced in neonatal mice is long-lasting; cells from these mice do not respond in culture and do not affect the response of normal cells. Evidently, antireceptor antibody reversibly blocks antigen receptors in adult animals, but induces unresponsiveness in neonatal mice by depleting the clone of receptor-bearing cells.

Restoration of immune competence in tolerant mice by parabiosis to normal mice

These studies demonstrate that mice tolerant to human gamma globulin (HGG) regain their ability to make antibody to HGG after parabiosis to normal mice. This can be demonstrated by enumeration of PFC in the spleens of both the normal and tolerant partners. Hemagglutinin titers of normal-tolerant parabionts, however, are exceptionally low; serum antibody appears to be neutralized by circulating HGG present originally in the serum of the tolerant partner. These data support the hypothesis that tolerance to HGG in mice is a "defective" state due to the absence of cells capable of responding to this antigen.

Cell-mediated immunity and blocking serum activity to tolerated allografts in rats

W/Fu rats were neonatally inoculated with bone marrow cells from B/N rats and vice versa. Of the inoculated rats, some were capable of accepting a foreign (B/N or W/Fu) skin graft over the period of observation (i.e. for more than 100 days), while other rats rejected their skin grafts as early as control animals (within 8-12 days) or after a prolonged period of acceptance (20-96 days). Using a microcytotoxicity test, it could be shown that both those rats that rapidly rejected skin grafts and those that kept their grafts during the observation period had lymphocytes capable of destroying cultivated allogeneic cells from the respective strains with whose cells the rats had been inoculated as newborns. The degree of lymphocyte reactivity decreased upon time, so that 4 of 13 rats that had carried "tolerated" skin grafts over more than 84 days had lymphocytes which were nonreactive in the highest dose tested, and the degree of reactivity in the other 9 rats was less than seen early after tolerance induction. Rats that were capable of accepting skin grafts over prolonged periods of time had sera that could specifically block lymphocyte-mediated cytotoxicity, while sera from rats that had rejected their grafts did not block. Sera from rats that rejected their skin grafts after 20-96 days lost the blocking activity 3-10 days before rejection.