Regulation of delayed-type hypersensitivity. V. Suppressor cell memory in antigen-specific suppression of delayed-type hypersensitivity to sheep erythrocytes

Suppression of antigraft immunity by preimmunization. V. Characterization of suppressor T memory cells

We have previously shown that after intravenous (i.v.) immunization of mice with allogeneic spleen cells, two populations of suppressor T (Ts) cells may occur that can suppress delayed-type hypersensitivity (DTH) to alloantigens: Ts effector cells that transiently occur in the spleen, and long-lived, recirculating Ts cells that occur in thoracic duct lymph and can be transferred by parabiosis. In this study, we investigated whether the latter Ts cells fulfill the criteria for memory T lymphocytes, such as induction by doses of antigen lower than required for T effector cell induction, accelerated onset of activity after reactivation and an increased activity as compared with virgin T cells. The Ts cells accounting for the long-lasting state of suppression of DTH to alloantigens indeed fulfilled these criteria. These Ts memory cells displayed the Thy-1+, L3T4-, Lyt-1+2+ phenotype.

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.

Antigen-specific augmentation of delayed-type hypersensitivity by immune serum factor in mice

The serum from C3H/He mice immunized with chicken erythrocytes (CRBC) in complete Freund's adjuvant contained a factor able to augment delayed-type hypersensitivity (DTH) antigen specifically, when transferred into naive syngeneic recipient mice before their sensitization with CRBC. This activity in immune serum appeared on Day 4 and reached a peak on Day 8 after immunization, and was enhanced when donor mice were treated with cyclophosphamide (CY) 2 days before immunization. The ability of recipient mice to respond to this factor was enhanced by CY treatment of these mice 4 days before being transferred. This factor could be discriminated from conventional antibodies. Production of this factor in the serum donor and the expression of its activity in transferred recipient was mediated by a T-cell subset which showed a low degree of thymus dependency in ontogenic development.

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.

Nonspecific suppression of anti-graft immunity by antigen-specific T suppressor cells

The specificity of T suppressor cells induced by intravenous administration of irradiated allogeneic spleen cells was studied in mice by means of a delayed type hypersensitivity (DTH) assay. T suppressor cells induced by either H-2K, H-2I or H-2D incompatible cells were found to be specific for the inducing alloantigen. Such antigen specific T suppressor cells can suppress the response to another H-2 alloantigen, provided it is administered together with the alloantigen that had induced the T suppressor cells. Similarly, T suppressor cells induced by non-H-2 alloantigens can suppress the response to H-2 alloantigens if administered simultaneously.