Genetic control and effector cells in host-versus-graft responses to H-Y antigen in mice

Impaired hematopoietic stem cell functioning after serial transplantation and during normal aging

Adult somatic stem cells possess extensive self-renewal capacity, as their primary role is to replenish aged and functionally impaired tissues. We have previously shown that the stem cell pool in short-lived DBA/2 (D2) mice is reduced during aging, in contrast to long-lived C57BL/6 (B6) mice. This suggests the existence of a genetically determined mitotic clock operating in stem cells, which possibly limits organismal aging. In the study reported here, unfractionated bone marrow (BM) cells or highly purified Lin(-)Sca-1(+)c-kit(+) (LSK) cells were serially transplanted in lethally irradiated D2 and B6 mice. In both strains, serial transplantation resulted in a substantial loss of stem cell activity. However, as we estimate that in B6 mice, the maximum number of population doublings of primitive cells is approximately 30, in D2 mice this is only approximately 20, resulting in a 1,000-fold difference in expansion potential, irrespective of whether whole bone marrow or purified hematopoietic stem cells (HSCs) were transplanted. Interestingly, recipients reconstituted with serially transplanted BM cells were able to accept a freshly isolated graft without any further conditioning. Finally, we show that whereas transplantation of BM cells into healthy, nonconditioned, young B6 recipients does not lead to engraftment, young BM cells do engraft and provide multilineage reconstitution in nonirradiated aged mice. Our data clearly establish the relevance of an intrinsic, genetically controlled program associated with impaired stem cell functioning during aging.

Rejection of H-Y Disparate Skin Grafts by Monospecific CD4+ Th1 and Th2 Cells: No Requirement for CD8+ T Cells or B Cells

We wished to determine whether CD4+ T cells could reject a skin graft that was discordant for a single minor transplantation Ag in the absence of CD8+ T cells or Ab. Transgenic A1(M) mice were constructed that express the rearranged Vβ8.2 and Vα10 TCR genes from a T cell clone that is specific for the male Ag (H-Y) in the context of H2-Ek. In addition, the RAG-1−/− background was bred onto these mice to eliminate any endogenous TCR rearrangements. As expected, clonal deletion was found to be complete in the thymus of male A1(M)×RAG-1−/− mice, while only CD4+ T cells were positively selected and found in the periphery of females. Female A1(M)×RAG-1−/− mice were able to rapidly reject (in <14 days) male (but not female) skin grafts in a CD4-dependent fashion. After multiple grafts, it was confirmed that no CD8+ T cells or surface Ig+ B cells were present. An immunofluorescent analysis of spleen cells after grafting showed that the majority of T cells expressed activation markers (CD44, CD25, and intracytoplasmic IL-2) and a significant proportion were making IFN-γ and IL-4. Surprisingly, the transfer of either Th1 or Th2 CD4+ T cell lines from these mice into T cell-depleted recipients was sufficient to cause a specific rejection of male skin.

A potential weak allelic difference in male-specific antigen between two inbred strains of mice

Differences were detected between male-specific antigen(s) from BALB/c and C57BL/10 mice. Reciprocal crosses between these strains were analysed by means of a popliteal lymph node assay enumerating cells secreting IgM and IgG in a T-dependent bystander B-cell response. The responses, while being indirect, weak and variable, suggested that there are differences in 'immunogenicity' coded by Y-linked (male-specific) genes. This conclusion was strengthened by the results of experiments carried out in Y-backcross mice, where spleen cells from male C57BL mice with a BALB/c-Y (B10.C-YC) stimulated low popliteal lymph node responses in female littermates in comparison with C57BL mice with their own Y-chromosome. In contradistinction, male spleen cells from a BALB/c with a C57B1/10-Y chromosome (C.B10-YB), injected into a hind footpad of a female littermate, induced a relatively higher popliteal lymph node response.

Delayed-type hypersensitivity to allogeneic mouse epidermal cell antigens. I. Lyt-1+2- T cells are important for DTH

Footpad swelling response was used to measure the alloantigenicity of epidermal cells (ECs) in delayed-type hypersensitivity (DTH). Strong footpad swelling was observed 3 h after the challenge, and it continued for 48 h after the challenge. Genetical incompatibility between the recipients and the ECs was required to induce significant footpad swelling. H-2 or non-H-2 incompatibility between mice and ECs in the sensitization phase sufficed to develop significant footpad swelling. Incompatibility caused by point mutation in the A region induced strong responses when B6.C-H-2bm12 mice were immunized with B6/J ECs, but the disparity in immunoglobulin h (Igh) allotype genes was insufficient. H-Y antigen on ECs could also elicit the DTH response. Semiallogeneic F1-derived ECs sensitized the parental recipients. The responses were successfully transferred by immune lymph node cells, but not by immune sera. Treatment of these immune lymph node cells with monoclonal antibodies plus complement revealed that the cells responsible for DTH transfer were Lyt-1+2-, Ia- T cells.

B-cell responses to male-specific antigen(s) in mice

It has been found that B-cell responses to male-specific antigen(s) can be clearly demonstrated by reversed plaque assays. Female mice injected with syngeneic male spleen cells showed significant increases (greater than 100 X in some strains) in the number of immunoglobulin-secreting cells in lymph nodes draining the injection site. There was a variation in B-cell responsiveness between strains and this correlated only partially with previously reported T-cell responsiveness to the H-Y antigen. C57BL (H-2b) mice were among the most responsive, while CBA (H-2k), (CBA X C57BL)F1, and BALB/c (H-2d) were all much less responsive. These results apparently open up a new approach to the investigation of B-cell responses to male-specific antigen(s).

Female popliteal lymph node responses to H-Y antigen on male thymocytes in mice. I. Regulation of primary and secondary responses by H-2-associated Ir genes

H-2-linked genes which control popliteal lymph node (PLN) immune responses to the H-Y antigen were analysed. It was found that at least two genes or two groups of genes are involved in the genetic control and are responsible for the four variants of relations observed between the primary and the secondary response: +/-, +/+, -/+ and -/- ('+' and '-' stand for a high and a low response, respectively). The results obtained with H-2 recombinant haplotypes indicated that the genes controlling the primary and secondary responses map to the left and to the right of the E alpha locus, respectively. A high primary response was observed in the presence of b alleles at K, A beta, A alpha, and E beta loci, whereas a high secondary response occurred only in the presence of d alleles in the chromosomal segment between E alpha and D loci. From the experiments with F1 hybrids it is clear that low secondary responses are, for the most part, dominant and that the two seemingly separate control mechanisms for the primary and secondary responses may interact.