Preliminary characterization of the cells causing an H-2-restricted GVH reaction.

An H-2-restricted graft-versus-host reaction can be demonstrated when irradiated bone marrow-protected recipients receive injections of cells from radiation chimeras. The cells responsible are Thy-1-positive, thymus-dependent, radiation-sensitive and pass through a nylon wool column, i.e., they are T cells. Treatment of the cells with anti-Lyt-1 or anti-Lyt-2 serum and complement reduces but does not eliminate the activity which can be eliminated by treatment with both antisera. Combining anti-Lyt-1-treated and anti-Lyt-2-treated cells does not restore the original activity.

H-2-restricted graft-versus-host reaction: foreign determinants and restriction elements.

Nylon-wool-purified T cells from radiation chimeras cause a lethal graft-versus-host reaction (GVHR) in irradiated, bone-marrow-protected recipients only if the recipient shares a restriction element with the T-cell donor and also expresses antigens foreign to the donor. Class I molecules (H-2K and H-2D) can act as restriction elements, but restriction to class II molecules could not be demonstrated. However, class II molecules as well as H-2K and some non-H-2 determinants could serve as foreign antigens.

Failure of parental T cells to restore T-cell deficient F1 mice.

The ability of normal, parental type T cells to initiate an immune response and to generate memory T cells in T-cell deficient F1 mice was investigated using two types of F1 recipients: Congenitally athymic (nude) mice and thymectomized, lethally irradiated, syngeneic bone marrow reconstituted (TIR) mice. In contrast to normal syngeneic T cells, normal parental type T cells elicited neither immune response nor memory T cells in F1 T-cell deficient mice. Parental T cells were ineffective even when obtained from chimeric donors tolerant to the second parental type transplantation antigens and normal, parental T cells did not counteract the restorative activity of F1 T cells in F1 T-cell-deficient recipients. These two latter findings exclude a suppression due to an ongoing GVH reaction as a possible cause for failure of parental T cells to restore F1 T-cell-deficient mice.

H-2-Restricted lethal graft-versus-host diseases.

T cells from radiation chimeras in several strain combinations cause lethal GVHD in irradiated, bone-marrow-protected mice which share the D end of the H-2 complex with the T cells and also have foreign determinants. This phenomenon was not found with T cells from normal mice. I suggest that H-2-restricted GVD cells may be present in normal mice, but their effects may be masked by unrestricted GVH cells, which however, develop more slowly in the chimeras so that lethality due to restricted cells can be observed.

Non-specific T-cell replacing factor fails to promote a secondary response in vivo.

The supernatant from concanavalin-A-treated cultures has been used in vivo in nude mice to investigate the nature of the antibody response that can be induced after injection of this non-specific T-cell replacing factor (NSF). Although NSF alone does not induce a response, it permits a greatly augmented response to sheep erythrocytes. This response is, however, restricted to IgM and is not accompanied by development of memory. No secondary response could be obtained with antigen alone or with NSF and antigen, and there was usually no response even if normal congenic thymus cells were injected with antigen into animals that had responded to NSF and antigen.

The relationship between alloantigen responses in nude mice injected with a low number of congenic thymus cells.

BALB/c-nu mice were injected with 10(6) normal congenic thymocytes. This number of cells permits only partial reconstitution and in individual mice some functions were restored and others were not. The relationships between the functions of skin graft rejection, circulating alloantibody production and the ability to generate, in vitro, cytotoxic T cells were studied with regard to the strains CBA and C57BL/6.

Restriction specificities, alloreactivity, and allotolerance expressed by T cells from nude mice reconstituted with H-2-compatible or -incompatible thymus grafts.

Congenitally thymusless nude mice that lacked functional T cells were reconstituted with H-2-compatible or -incompatible thymus grafts taken from either fetal, newborn, or adult mice and transplanted under the kidney capsule or subcutaneously. Transplantation with unirradiated fetal (15--17 d) or newborn thymus grafts reconstituted the nude mice as assessed by their subsequent generation of virus-specific cytotoxic T cells in vivo or alloreactive T cells in vitro. The restriction specificity of T cells from homozygous mice was exclusively for the nude host H-2, as shown by direct cytolysis or by cold target competitive inhibition assays. irrespective of whether nude mice were reconstituted with H-2-compatible, semiallogeneic, or H-2-incompatible, unirradiated newborn or fetal thymus grafts (in order of decreasing efficiency of reconstitution). The restriction specificity for the nonhost H-2 of the thymus could not be demonstrated even after primary or secondary sensitization in an infected appropriate F1 environment. These nude mice reconstituted with fetal or newborn grafts were tolerant to the H-2 of the thymus donors. Nude mice transplanted with irradiated adult thymus grafts were reconstituted functionally with syngeneic or semisyngeneic but not with allogeneic thymus grafts. In homozygous nu/nu irradiated heterozygous recipients of F1 thymus grafts, the restriction specificity for the nonhost thymic H-2 could not be elicited upon adoptive sensitization in irradiated and infected F1 heterozygote stimulator mice; in fact, these chimeras' lymphocytes were not tolerant to the nonhost H-2. The discrepancy between the restorative capacity of unirradiated vs. irradiated thymus grafts suggests that precursors of T cells in nude mice can acquire restriction specificity and immunocompetence independently of a conventional, functioning H-2-compatible thymus if exposed to an allogeneic fetal or a newborn thymus that contains functioning thymocytes of donor type but not if reconstituted with an irradiated adult allogeneic thymus.

In vivo activity of a nonspecific T cell-replacing factor.

Nonspecific T cell-replacing factors prepared as supernatants from mixed lymphocyte cultures or concanavalin A-stimulated spleen cells are active in vivo iv injected into nude mice at least 3 days before antigen. The supernatants appear to act by enhancing the week IgM responses that occur in untreated nudes. Secondary responses and IgG antibody were not found.

Specificity of helper T cells for different antigens.

BALB/c nude mice have been injected with 10(6) congenic thymus cells, a number which allows some, but not all mice to respond to any particular T-dependent antigen. These mice have been tested for their ability to respond to three bacteriophages, T4, T7 and phiX, sheep and horse erythrocytes, and alloantigens of C3H and C57BL/6 mice. The number of mice able to respond to each of these antigens was of the same order of magnitude. Sheep and horse erythrocytes showed cross-reactivity at the T cell level, i.e. the responses to these two antigens were not independent. The same was observed for C3H and C57BL/6. Otherwise, the responses were independent showing that the antigens are recognize by different populations of specific helper T cells.