Analyses of H-2 restriction specificity of helper T cells in fully allogeneic bone marrow chimera in mice

Positive and negative selection of T cell repertoires during differentiation in allogeneic bone marrow chimeras

T cells acquire immune functions during expansion and differentiation in the thymus. Mature T cells respond to peptide antigens (Ag) derived from foreign proteins when these peptide Ag are presented on the self major histocompatibility complex (MHC) molecules but not on allo-MHC. This is termed self-MHC restriction. On the other hand, T cells do not induce aggressive responses to self Ag (self-tolerance). Self-MHC restriction and self-tolerance are not genetically determined but acquired a posteriori by positive and negative selection in the thymus in harmony with the functional maturation. Allogeneic bone marrow (BM) chimera systems have been a useful strategy to elucidate mechanisms underlying positive and negative selection. In this communication, the contribution of BM chimera systems to the investigation of the world of T-ology is discussed.

Influence of graft versus host reaction on the T cell repertoire differentiating from bone marrow precursors following allogeneic bone marrow transplantation

When lethally irradiated AKR (Mls-1a) mice were reconstituted with bone marrow (BM) cells plus a small number (0.5%) of mature T cells from allogeneic B10.AQR or B10 (Mls-1b) mice and minor GVHR was induced in the recipients, almost complete donor chimerism was accomplished in the early stages after reconstitution. By contrast, in irradiated AKR mice reconstituted with T cell-depleted BM cells alone from B10 or B10.AQR mice, radio-resistant T cells of recipient origin persisted for a relatively long period in peripheral lymphoid tissues. In this paper the influence of residual T cells in the chimeric mice on generation of the T cell repertoire derived from donor BM is discussed. It will be demonstrated that the recipient (AKR) T cells are capable of producing Mls-1a antigens (Ag) after lethal irradiation in vivo. These recipient T cells eventually induce clonal elimination of Mls-1a reactive V beta 6+, V beta 8.1+ and V beta 9+ T cells derived from developing thymocytes of donor BM origin. The Mls-1a reactive T cells are not eliminated in GVHR chimeras in which recipient T cells are absent. However, V beta 5+ T cells reactive to I-E plus Etc-1 Ag are deleted in the chimeras undergoing GVHR. These results indicate that recipient cells which produce tissue-specific antigens (tolerogens) should be taken into consideration when generation of the T cell repertoire of donor origin following allogeneic BM transplantation is investigated.

Influence of a small number of mature T cells in donor bone marrow inocula on reconstitution of lymphoid tissues and negative selection of a T cell repertoire in the recipient

Allo-chimerism and clonal elimination of self antigen (Ag) (Ia + Mls-1a) reactive V beta 6+ T cells were analyzed and compared between allogeneic bone marrow (BM) chimeras reconstituted with BM cells which had been treated with anti-Thy-1 monoclonal antibody (mAb) plus complement (C) (T- chimeras) and BM chimeras which had been reconstituted with BM cells pretreated with anti-Thy-1 mAb alone (T+ chimeras). When lethally irradiated AKR (Mls-1a) mice were reconstituted with BM cells from B10 or B10 H-2 congenic mice, both T+ and T- chimeras were entirely free of signs of graft-versus-host reaction (GVHR). However, complete replacement of the AKR lymphoid tissues by donor BM cells was accomplished at an early stage in T+ chimeras but not in T- chimeras. On the other hand, clonal elimination of V beta 6+ T cells reactive to the recipient Ag (Mls-1a) was abolished in T+ chimeras but successfully induced in T- chimeras. The V beta 6+ T cells not eliminated in T+ chimeras showed depressed responses against Mls-1a antigens. The findings herein demonstrate that T cells which contaminate a BM inoculum survive in recipient mice after treatment with anti-Thy-1 mAb without C in vitro followed by BMT. The surviving T cells have been estimated to represent fewer than 0.5% of the BM cells inoculated. These cells appear to accelerate the full replacement of recipient lymphoid tissues by donor cells. Furthermore, the T cells which survive in the marrow inoculum influence eventually the development of a tolerant state in the T cell repertoire of the donor.

H-2K molecules positively select V beta 17a+ CD4(-)8+ T cells in bone marrow and thymic chimeras

Population size of V beta 17a brightly positive cells among CD4(-)8+ thymocytes was analyzed in thymic chimeras as well as bone marrow (BM) chimeras in which SWR/J mice were used as BM donors and various strains of mice including H-2Kb mutant (bm) mice as recipients. It was shown that the proportion of V beta 17a+ CD4(-)8+ thymocytes was determined by H-2K molecules expressed on thymic epithelial cells. The highest proportion was observed in Ks and Kb thymuses, the intermediate proportion in Ks/q and Kk, and the lowest in Kq thymuses. Fine analysis of the H-2Kbm molecules involved in the positive selection revealed that the region important to the selection was located on the beta-pleated floor of antigen recognition site. According to the three-dimensional class I structure, this site appears not to be directly accessible to the T cell antigen receptor. Thus, the present finding suggests that the substitutions of amino acids at this site alter the shape and charge of the peptide binding site and eventually influence the positive selection of the V beta 17a+ T cell repertoire during differentiation.

Ia restriction specificity of KLH-specific T cells from allogeneic bone marrow chimeras is influenced by histocompatibility at the H-2 and minor histocompatibility loci

Ia restriction specificity involved in T cell proliferative responses to keyhole limpet hemocyanin (KLH) has been analyzed using a variety of allogeneic bone marrow chimeras. The chimeric mice were prepared by reconstituting irradiated AKR, SJL, B10.BR and B10.A(4R) mice with bone marrow cells from B10 mice. When such chimeric mice had first been primed with KLH in complete Freund's adjuvant (CFA), T cells from H-2 incompatible fully allogeneic chimeras showed significantly higher responses to KLH in the presence of antigen-presenting cells (APC) of donor strain (B10) than APC of recipient strain. However, in H-2 subregion compatible chimeras, [B10----B10.A(4R)], which were matched at the H-2D locus and at minor histocompatible loci, the T cells could mount vigorous responses to KLH with antigen-presenting cells (APC) of either donor or recipient type. The same results were obtained as well with chimeras that had been thymectomized after full reconstitution of lymphoid tissues by donor-derived cells. A considerable proportion of KLH-specific T cell hybridomas established from [B10----B10.A(4R)] chimeras exhibited both I-Ab and I-Ak restriction specificities. The present findings indicate that the bias to donor Ia type of antigen specific T cells is determined by donor-derived APC present in the extrathymic environment but that cross-reactivity to the recipient Ia is influenced to some degree by histocompatibility between donor and recipient mice, even though the histocompatible H-2D locus and minor histocompatibility loci seem not to be directly involved in the I-A restricted responses studied herein.

Sequential analysis of distributions of donor-derived thymocytes bearing T-cell antigen receptor (TCR) and donor-derived Ia+ cells in thymuses of fully allogeneic bone marrow chimera in mice

Lethally irradiated SJL/J mice were reconstituted with B10 bone marrow cells, and the process of thymic reconstitution by donor-derived cells positive for I-A or V beta 8 molecules was investigated. The donor-derived Ia+ cells appeared in the medulla on day 7 after reconstitution. The Ia+ cells became confluent up to day 14, and the cellularity in the medulla on day 17 was almost the same as that in the normal thymus. Dull V beta 8+ thymocytes were first recognized in the cortex on day 10 and were identifiable in the medulla by day 14. The V beta 8+ cells seemed to be mainly CD4+8+ double-positive. Furthermore, most of the V beta 8+ cells in the medulla of chimeras given cyclosporin A for 3 weeks after reconstitution appeared to be CD4+8+ thymocytes which bear a low concentration of TCR exist in the thymic medulla at a relatively early stage when donor-derived Ia+ cells have already settled there. The coincidental appearance and coexistence of Ia+ cells and TCR+ thymocytes in the medulla suggest that these histological characteristics may be related to the selection of thymocytes in this area.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. II. Further characterization of the CD4+ or CD8+ single positive thymocytes

Differentiation of CD4+8- and CD4-8+ single-positive (SP) thymocytes in fully allogeneic bone marrow chimeras were investigated using multicolor cytometric analysis. The proportion of CD3+ cells in CD4+ SP population derived from donor mice considerably increased between day 12 and 14 after bone marrow transplantation (BMT), and gradually increased thereafter. The proportion of V beta 8+ cells in the CD3+CD4+ population remained constant (around 20%) at each period, suggesting that alpha and beta chains were used as TCR. The proportion of J11d+ cells in the CD4+ SP thymocytes transiently increased from day 12 to 14 and decreased thereafter, even though almost half of CD4+ SP cells were still dull J11d+ at day 35 after BMT. When CD8+ SP populations were analyzed, the proportion of CD3+ cells was very small until day 18. Thereafter, the proportion considerably increased and reached a maximum (83.2%) at day 21. The proportion of V beta 8+ cells in the CD3+ CD8+ SP population fell within range between 20 and 30%. However, before day 18, most of the V beta 8+ cells were dull positive, while after day 21 the majority were bright V beta 8+. Further, CD8+ SP cells at day 12, 14 and 18 were largely bright J11d+. After day 21, however, the proportion of bright J11d+ cells rapidly decreased. Similar results were obtained when the sequence of appearance of CD4+ and CD8+ SP cells was compared among bright CD3+, bright V beta 8+ or J11d- mature populations. The CD4+ SP cells regularly appeared earlier than CD8+ SP cells in the mature populations. These findings indicate that a considerable heterogeneity exists within both CD4+ and CD8+ SP populations and that the differentiation process for CD4+ SP cells precedes that for CD8+ SP cells.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. I. Relationship between functions and surface characteristics of thymocytes

Differentiation of thymocytes according to surface phenotype, functional status and cell size was investigated using fully allogeneic bone marrow chimeras. Most of the donor-derived thymocytes obtained from chimeras 9 days after hematopoietic reconstitution were CD4-8- and IL2R+. At day 14, CD4+8+ cells became prominent in the thymus. Eighty-six per cent of thymocytes were CD4+8+ and 9% were CD4-8- at this stage. After day 21, the proportion of CD4+8- or CD4-8+ single positive cells transiently increased and then declined to normal level at day 42. Further, the mean size of CD4+ or CD8+ single positive cells in chimeric thymuses at day 21 after reconstitution was markedly larger than that at day 35. When proliferative responses to various stimuli (PMA + rIL2, anti-CD3 mAb (2C11) and anti-V beta 8 mAb (F23.1] were evaluated, significant responses were generated by thymocytes for the first time at around day 28 and the responses reached their peaks at day 35. These findings demonstrated that the process of thymocyte differentiation in the fully allogeneic chimeras was similar to ontogenic development as observed in fetal mice. However, the tempo at which the differentiation of surface phenotypes and development of functions proceeded was quite different from that seen in normal mice. The relationship among surface phenotypes, cell size and functions of developing thymocytes of bone marrow chimeras is discussed.

Positive selection of a T-cell subpopulation in the thymus in which it develops

In SWR mice the expression with high-density V beta 17a (high V beta 17a) of the T-cell antigen receptors correlates with the CD4+8- subpopulation of thymocytes. By contrast, in thymocytes of SJL mice the expression of high V beta 17a is observed on the CD4+8- or CD4-8+ subpopulation. However, when the thymocytes from SWR mice have been developed in the SJL or B10 thymus but not in the H-2 compatible DBA/1 thymus, a greater proportion of thymocytes that express high V beta 17a was found to be CD4-8+. By contrast, only a small proportion of KJ23a+ thymocytes from SJL mice that had differentiated in the thymus of SWR or DBA/1 mice was CD4-8+, whereas a high proportion of CD4+8- cells expressed V beta 17a. Further, an intermediate proportion of KJ23a+ thymocytes that had derived from SJL donor mice was present on CD4-8+ thymocytes that had developed in B10.A(4R) thymus. These findings demonstrate that the appearance of a particular subpopulation of thymocytes (CD4-8+ with a beta chain of T-cell antigen receptor identified as V beta 17a) is determined by the histocompatibility complex products that are expressed in the thymic microenvironment in which the T cells develop.

Donor and recipient specific tolerance in cells from semi-allogeneic, H-2 subregion compatible or fully allogeneic bone marrow chimeras attributable to clonal deletion

Specificities of tolerance induced in allogeneic bone marrow (BM) chimeras which had been established by injecting allogeneic BM cells pretreated with anti-Thy-1 mAb alone (without complement (C)) were analyzed using Simonsen's splenomegaly assay. Lymphocytes from fully allogeneic, semi-allogeneic and H-2 subregion compatible BM chimeras were specifically unresponsive to donor and recipient antigens (Ag). However, cells from H-2 subregion compatible chimeras initiated as vigorously a GVHR in F1 recipient mice, which were disparate at H-2K and I-A regions, as did spleen cells of donor mice, which were incompatible at the entire H-2 and minor histocompatibility regions of the recipients. The donor cells from such chimeras that initiated these considerable GVHR were either CD4+ or CD8+ T cells. Furthermore, synergistic effects by the CD4+ and CD8+ T lymphocytes were also observed. We found no evidence for a suppressive mechanism(s) in maintenance of the specific tolerance in allogeneic chimeras. Further, when lymphoid cells from these chimeras were adoptively transferred to irradiated mice of the donor strain and maintained for 5 days in the absence of recipient Ag (tolerogen), the adoptively transferred cells were shown to retain their unresponsiveness to the recipient Ag. These results reveal that T lymphocytes from allogeneic BM chimeras prepared by our method had been specifically induced to a tolerant state to both donor and recipient Ag and that the major mechanism of induction and maintenance of long-lasting tolerance is attributable to clonal deletion of both CD4+ and CD8+ T cell subsets rather than to the development of a population of suppressor cells of any sort.

Strain differences in the early development of the thymus-dependent cells: precocity of T lineage cells in AKR mice as compared to those in C3H mice

Early development of T lineage cells were compared between AKR and C3H mice by using two experimental strategies--neonatal thymectomy (NTx) and bone marrow transplantation (BMT)--between these two strains of mice. After NTx, AKR mice developed less wasting disease and showed better maintenance of several T cell functions. In addition, the response of neonatal spleen cells to PHA and ConA was much greater in AKR mice than in C3H mice. Further, when AKR mice were used as recipients of BMT, cell numbers recovered from thymuses between 2 and 7 weeks after reconstitution were consistently much greater (about 10 times greater) than those from chimeras where C3H mice were used as recipients, regardless of the donor strains of bone marrow cells. However, 4 weeks after BMT the proliferative responses to ConA were consistently higher in the donor-derived thymocytes from chimeras where AKR mice were used as bone marrow donors than in those from chimeras in which C3H were donors. The present findings suggest that these differences may be attributed to characteristics of recipient microenvironment (e.g., thymic stroma) which maintain developing thymocytes and supply them to the peripheral lymphoid tissue. Alternatively the differences may to some degree also be attributable to characteristics of the thymic progenitors themselves, which may determine the rates of maturation of thymocyte functions.

Generation of cytotoxic T lymphocyte responses to allo-H-2 antigens in allogeneic bone marrow chimeras histocompatible at the H-2 subregions

The present study was performed to determine whether H-2 matching is required for full cytotoxic T lymphocyte (CTL) responses to allo-H-2 antigens in allogeneic bone marrow chimeric mice. A number of irradiated, bone marrow-reconstituted chimeras constructed from various combinations of marrow cells from B10 H-2 recombinant strains and AKR recipient mice were prepared. Spleen cells obtained from such chimeras and normal control mice were activated in vitro by culturing them with irradiated stimulator cells. It was shown that spleen cells from [4R----AKR], [(4R X 3R)F1----AKR] or [AQR----AKR] chimeras, which were histocompatible on the left hand-side of the H-21 subregion between donor and recipient mice, generated greater CTL activities than those that were seen with spleen cells of [3R----AKR] or [5R----AKR] chimeras, which were histoincompatible in this region. We were unable to demonstrate suppressor cell activity of the spleen cells of [3R----AKR] chimeras cultured with stimulator cells. Although spleen cells from [3R----AKR] chimeras showed substantial proliferative responses to stimulator cells (MLR) and to Con A and LPS, IL2 activities of supernatants from Con A-activated spleen cells (Con A SN) of the chimeras were significantly lower than those of [4R----AKR] or [(4R X 3R)F1----AKR] chimeras. Furthermore, vigorous CTL activities were obtained with either spleen cells or thymocytes from [3R----AKR] chimeras when rat Con A SN was added to the MLR cultures. These observations suggest that the numbers of precursor CTLs in the cells from [3R----AKR] chimeras are at the same level as those of [(4R X 3R)F1----AKR] or normal mice and that the low CTL activities generated by spleen cells of [3R----AKR] chimeras compared to H-2I-matched chimeras are due in large measure to deficiency in IL2 production by the splenic T cells of the [3R----AKR] chimeras.

Analyses of Ia restriction specificity of helper T cells in H-2 subregion compatible bone marrow chimera in mice

Using irradiation bone marrow chimeras which had partial compatibility in H-2 subregions between donor and recipient mice, we found that H-2I matching was sufficient for the chimeras to generate anti-sheep erythrocyte plaque-forming cell (PFC) responses. In such chimeras, T cells appeared to encounter appropriate partner cells bearing the same Ia antigens as those which they had learned to recognize as self in the recipient micro-environment. Furthermore, the PFC number seen in I-A compatible chimeras was only about half of that seen in I-A, I-E compatible chimeras, suggesting the existence of two independent subpopulations of helper T cells. When incompatibility of donor and recipient mice existed on the left side of the H-2I region, the responses were very weak. However, even in such chimeras, marked responses were observed for both IgM and IgG type PFC following a sufficient period after immunization. This observation appears to indicate the existence of a minor subpopulation of helper T cells which can expand and interact effectively with antigen presenting cells of donor type.