Cellular control of lymphocytes initiating graft vs. host reactions

Analysis of neonatally induced tolerance of H-2 alloantigens. II. Failure to detect alloantigen-specific T-lymphocyte precursors and suppressors

There is a considerable amount of evidence, confirmed and extended by our studies, in favor of clonal deletion of alloantigen-reactive cells in neonatally induced transplantation tolerance. We have demonstrated in adult mice bearing long-standing skin allografts that lymphocytes specifically reactive with the tolerated H-2 alloantigens are undetectable by mixed lymphocyte and graft-versus-host reactions, and in cell-mediated lympholysis. In addition, lymphoid cells capable of suppressing the reactivity of syngeneic normal lymphocytes in these assays similarly escape detection. Moreover, putative precursors of T cells specific for the tolerated antigens cannot be activated polyclonally with concanavalin A (Con A), nor can they be identified among thymocytes of H-2-tolerant mice. Since the tolerant state can be adoptively transferred with lymphohematopoietic cells to adult, syngeneic mice, we infer that transplantation tolerance is maintained by an active process that achieves specific clonal deletion at an early stage in the ontogeny of alloreactive T lymphocytes.

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.

Ultrastructural findings in the mouse exocrine pancreas during graft-versus host reaction

12- to 36-hours-old newborn CBA mice were intraperitoneally injected each with 10 X 10(6) allogeneic spleen cells of adult C57Bl mice. Control mice received syngeneic spleen cells of adult CBA mice either in the same way or remained untreated. The animals were killed 1, 3, 7, 14 or 21 days after the spleen cell injection. The pancreas was studied histologically and electron microscopically by common methods. Together with an interstitial lymphohistiocytic infiltration of the pancreas different acinar cell alterations were observed in the mice treated with allogeneic spleen cells: 1. Acute lethal pancreatic cell damages on the day after the intraperitoneal injection of allogeneic spleen cells. 2. Membrane-lined inclusion vacuoles between the 7th and 21st experimental day. 3. Atrophy of pancreatic acinar cells in the terminal stage of a severe graft-versus-host disease. The pathogenesis of the observed pancreatic changes seems to be due to nonimmunological and immunological processes. The membrane-lined inclusion vacuoles of the acinar cells could be the consequence of a cell-mediated immune process in the graft-versus-host reaction.

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.

Changes in lymphocyte recirculation and liberation of the adoptive memory response from cellular regulation in irradiated recipients

Thoracic duct lymphocytes from previously immunized (AS2 x AS)F1 rats ('TDL) were adoptively transferred to syngeneic recipients and triggered by soluble HSA (s-HSA) the following day. The response of 'TDL in an irradiated recipient was almost two orders of magnitude greater than the response in a nonirradiated adult host. The affinity of the antibody in the adult recipients was significantly reduced but increased with time. Nonirradiated young recipients (3 weeks old) also supported an adoptive memory response which was comparable in quantity and quality to that found in irradiated hosts. The response of 'TDL declined progressively when transferred into 2-week-old or 4-week-old radiation chimeras, or was reduced in irradiated hosts when the memory cells were mixed together with nonimmune TDL. The experiments indicate that the differential response between the adult and irradiated recipient is the result of a restrictive control in the former host rather than an enhancing factor in the latter. Lymphocytes in the nonimmune population regulate both the expansion and maturation of the adoptive memory response, the high energy-binding B cells being at a selective disadvantage. Host irradiation effectively liberates the adoptive response from this cellular control mechanism. A comparative study of transferred, [14C]leucine-labeled TDL showed that distribution and homing of lymphocytes to lymph nodes and spleen was not altered by irradiating the recipients. However, adoptively transferred cells almost completely failed to recirculate in irradiated rats, in contrast to normal recipients. But, the injection of large numbers of unlabeled TDL following irradiation forced more labeled cells into the recirculating pool, suggesting that saturation of depleted lymphoid tissue with lymphocytes is an important factor regulating lymphocyte traffic. The relevance of this "saturation effect" in regulating the adoptive memory response is discussed.

Suppression of contact sensitivity by T cells in the mouse. I. Demonstration that suppressor cells act on the effector stage of contact sensitivity; and their induction following in vitro exposure to antigen

Mice injected intravenously with picryl sulphonic acid (PSA) fail to show contact sensitivity when subsequently immunized and challenged with picryl chloride applied to the skin. The injection into normal recipients of lymph node (and to a lesser extent, spleen and bone marrow cells) from mice treated with PSA, depressed the contact sensitivity which otherwise followed immunization by picryl chloride applied to the skin. Experiments were designed to show the location of the block in the development of contact sensitivity. Lymph node cells from mice treated with PSA (‘suppressor cells’) blocked the effector stage of contact sensitivity. This was shown by taking advantage of the fact that contact sensitivity to picryl chloride can be transferred to normal recipients by lymph node cells from mice immunized with picryl chloride (immune lymph node cells). The contact sensitivity is detected by applying picryl chloride to the ears of the recipients and measuring the increase in thickness at 24 h. The addition of lymph node cells from mice treated with PSA (suppressor cells) to the immune lymph node cells limited passive transfer of contact sensitivity. Although suppressor cells limited passive transfer they had little or no ability to depress the DNA synthesis which occurs in draining lymph node following skin painting with picryl chloride. Lymph node cells from mice treated with PSA do not immediately develop the ability to limit the passive transfer of contact sensitivity. PSA was injected into normal mice and their lymph node cells taken at various times afterwards. These cells first depressed the passive transfer of contact sensitivity when taken at 4 days. In contrast, cells taken after one day depressed the development of contact sensitivity when injected into normal mice which were then sensitized with picryl chloride and challenged 6 days later. Both these activities were present at day 10 and were waning by day 14. The depression of contact sensitivity by suppressor cells was specific. Cells from mice treated with PSA did not depress contact sensitivity to ‘oxazolone’. Moreover, these cells failed to block the passive transfer of contact sensitivity to ‘oxazolone’ even when the recipients were challenged with a mixture of picryl chloride and ‘oxazolone’. Lymph node cells treated for 2 h in vitro with PSA also blocked the development of contact sensitivity. T cells were probably involved, as treatment with anti-theta antibody and complement before incubation with PSA abolished this effect. Thymus cells were ineffective unless they were treated with neuraminidase. The hypothesis was put forward that the injection of PSA gives rise to an immunological response which generates specific suppressor cells.

Deficit of specific thymus-dependent lymphocytes in transplantation tolerance in the rat

Recovery from adoptively terminated transplantation tolerance was studied by utilizing formerly tolerant rats as donors of lymphocytes in local renal graft-vs.-host reactions (GVHR). The origin of the proliferating lymphocytes in the GVHR was studied by means of sex chromosome markers. A deficit of specifically reactive lymphocytes, while tolerance was in effect, was revealed by the continuing absence of autochthonous specifically reactive cells after tolerance was abolished in adult thymectomized chimeras. The findings are consistent with Burnet's hypothesis of the cellular basis of tolerance, but apply only to the T lymphocytes of donor origin which normally proliferate in these GVHR.

Active suppression as a possible mechanism of tolerance in tetraparental mice

Previous work has indicated that tetraparental mice, chimeric since the eight-cell stage because of embryo fusion using histoincompatible strain combinations, possess autospecific immune cells and blocking antibodies. Although this phenomenon has been demonstrated in vitro, it may have relevance to the self-tolerance shown by these mice in vivo. The experiments described here indicate that spleen cells from tetraparental mice can block mixed lymphocyte reactions between the two parental cell types, but not between unrelated strains. Furthermore, this suppressive ability is not affected by an otherwise effective treatment of the tetraparental spleen cells with anti-theta antibody and complement. The in vitro experimental system elaborated here should help to characterize the cell type responsible for the suppression.