Different H-2-subregion-coded antigens as targets for T-cell subsets synergizing in graft-versus-host reaction

Spleen cells from antithymocyte serum pretreated mice do not induce GVHD but exert increased repopulating activity in irradiated semiallogeneic recipients

Graft-versus-host disease (GVHD) due to allogeneic bone marrow transplantation can be prevented by depleting the T cells from the marrow graft in vitro. However, the elimination of the donor T cells results in a higher frequency of graft failure, secondary infections and, in case of leukaemia, relapse. We found, that, in contrast to normal spleen cells, spleen cells from A or B10 donor mice pretreated with xenogeneic antithymocyte serum (ATS) in vivo did not induce GVHD in non-irradiated (B10 x A)F1 hybrids. Spleen cells of ATS-pretreated A donors did not cause GVHD in allogeneic CBA mice made neonatally tolerant to the A donor strain either. Furthermore, spleen cells from ATS-treated donors did not cause GVHD in irradiated F1 hybrid recipients, moreover, they decreased the lethal effect of irradiation. The in vivo ATS pretreatment improved the repopulating capacity of spleen cells in irradiated syngeneic recipients, too. The effect of the ATS treatment does not rely solely upon the elimination of T cells, since flow cytofluorometric analysis revealed only a partial depletion of both the CD4+ and CD8+ T cells of the ATS-pretreated animals. These observations may also have clinical relevance.

Regulation of delayed type hypersensitivity to host histocompatibility antigens during graft-versus-host reactions

During GvH reactions in irradiated mice a variety of specific anti-host immune responses may occur. One of these is the occurrence of DTH to the host histocompatibility antigens, which may account for the inflammatory aspects of GvH. During acute as well as delayed GvH reactions the occurrence of anti-host DTH precedes the clinical symptoms of GvH disease. The anti-host DTH is mediated by long-lived, recirculating Lyt-1 + 2- T cells that need to proliferate in the irradiated recipients in order to display maximum activity. Not all host histocompatibility antigens can elicit anti-host DTH. H-2I and Mls-locus coded alloantigens do, but H-2K/D coded alloantigens and non-H-2 alloantigens other than Mls-locus coded alloantigens do not. This correlates with the ability to elicit proliferative mixed lymphocyte reactions in vitro but is in contrast to the response of nonirradiated mice to sc administered alloantigens. Under the latter conditions, all histocompatibility antigens induce a state of antigen-specific DTH. While the anti-host DTH is mediated by long-lived, recirculating Lyt-1 + 2- T cells, their response can be amplified by short-lived, sessile Lyt-1 + 2 + T cells. The latter T cell subset reacts to the host H-2K/D alloantigens and/or to non-H-2 alloantigens other than Mls-locus coded products. These cells alone cannot mount an anti-host DTH response. The anti-host DTH can be mitigated by Ts cells and non-T suppressor cells. Appropriate Ts cells can be readily induced by iv preimmunization of the donors with 5 X 10(7) irradiated, recipient-type spleen cells. Non-T suppressor cells can be induced by iv injection of bacterial LPS and simultaneous sc injection of 1 X 10(7) recipient type spleen cells. The suppression induced by these protocols shares several characteristics. In both cases the suppression is long-lasting, i.e., lasts at least 50 d, is transferable to syngeneic mice by spleen and lymph node cells, and both suppressive systems affect the induction of anti-host DTH as well as already activated anti-host DTH reactive T cells. Furthermore, while Ts cells and non-T suppressor cells are specific with regard to their antigen recognition, they are both able to suppress the DTH to a completely different set of host alloantigens. This, however, only occurs if the latter are inherited by the irradiated recipients as bystanders to the type of alloantigens that had activated the suppressor cells in the lymphoid cell donors.

Augmentation of natural killer cell activity by anti-host delayed-type hypersensitivity during the graft-versus-host reaction in mice

During a graft-versus-host (GVH) reaction in unirradiated F1 hybrid mice there is a generalized activation of natural killer (NK) cells. We have examined whether the enhanced NK activity is due to an F1 resistance mechanism directed at the parental cells used to induce the GVH reaction. Spleen cells of C57BL/10 origin induce much more NK cell activation in B10F1 hybrids than the opposite parental type, despite a similar intensity of systemic GVH reactions. However, this does not correlate with in vivo resistance of mice with GVH reaction to a local challenge dose of B10 cells. NK cell activation in (CBA X BALB/c)F1 mice with GVH reaction involves both host and donor cells and is preceded by an anti-host delayed-type hypersensitivity (DTH) response. B10 cells have a greater ability to induce DTH in B10F1 mice than cells from the opposite parent. We propose that NK cells are one group of non-specific effector cells recruited by DTH in a GVH reaction and may contribute to the tissue pathology.

Characterization of suppressor T cells in graft-versus-host reactions

Intravenous (i.v.) immunization of mice with irradiated (2000 rads) allogeneic lymphoid cells induces the generation of suppressor T cells. Such suppressor T cells can suppress the anti-host delayed type hypersensitivity (DTH) by other T cells during acute Graft-versus-Host reactions in irradiated recipient mice. Suppression of anti-host DTH is detectable at least 50 days after i.v. induction of the state of suppression in the donors. The generation of suppressor T cells in the donors is associated with proliferation. Furthermore, the suppressor T cells need to proliferate further in the irradiated allogeneic hosts in order to display a maximal suppressive effect. Two types of suppressor T cells were found to be required for suppression of the anti-host DTH response: a Lyt-1+2- cell population and a Lyt-1-2+ cell population.

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Synergism of T lymphocyte subsets in the response to Mls-locus coded antigens during graft-versus-host reaction

After transplantation of lymphoid cells into lethally irradiated (semi)allogeneic mice specific anti-host directed effector T cells are generated. This can be demonstrated using a delayed type hypersensitivity (DTH) assay. In H-2 compatible combinations, Mls-locus antigens, but no other minor histocompatibility antigens, can induce the generation of such effector T cells. This paper shows that maximal anti-host DTH responses are obtained when the lymphoid cells transplanted constitute of a mixture of long-lived, recirculating T2 cells and short-lived, sessile T1 cells. It was demonstrated that anti-Mls locus-directed DTH effector T cells are the progeny of T2 cells, and that T1 cells amplify this response. The latter, however, are by themselves incapable of displaying anti-Mls DTH reactivity. The T1 cells were found to be of the Lyt-1+2+ phenotype, and the T2 cells of the Lyt-1+2- phenotype. The same Lyt phenotypes were found for T1 and T2 cells synergizing in the GvH reaction against H-2 alloantigens.