Contrasting feature in the repopulation of host-type T cells in the spleens of F1----P and P----F1 radiation bone marrow chimeras

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.

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.

Study on the possible factors influencing the expression of H-2 restriction specificity and Ir phenotype of antigen-specific proliferative T cells with various types of radiation chimeras

To better understand the factors described previously as influencing the manifestation of H-2 restriction specificity and Ir phenotype of T cells from radiation bone marrow chimeras, we also examined H-2 restriction specificity (Ir phenotype) of antigen (DNP-OVA, (T, G)-A-L, (H, G)-A-L)-specific proliferative T cells generated in various types of H-2 incompatible radiation chimeras prepared under our specific-pathogen-free (SPF) condition. The results indicated the following: (a) T cells generated in F1----parent bone marrow chimeras preferentially manifested host-type H-2 restriction specificity and Ir phenotype, regardless of the radiation dose (8.70 vs 11.59 Gy); (b) T cells recovered from twice-reconstituted F1----(PA----PB) chimeras manifested primary host (PB)-type Ir phenotype; (c) T cells which were recovered from (B10.Thy-1.1 X B10.BR.Thy-1.1)F1----parent (Thy-1.2) bone marrow chimeras and treated with anti-Thy-1.2 plus complement to deplete host-derived T cells still manifested preferentially the restriction specificity for host-type H-2; (d) PA-derived T cells which had differentiated in a fully allogeneic host (PB) environment of (PA + PB)----PB chimeras manifested fully allogeneic host-type Ir phenotype; (e) T cells from F1----parent chimeras that were prepared with 13-day fetal liver cells also manifested host H-2-restricted Ir phenotype; and (f) host preference for Ir phenotype of antigen-specific proliferative T cells was observed even in the case of F1----parent bone marrow chimeras reconstituted with "intact" bone marrow cells. The data suggest that thymic APCs, surviving host T cells or the source of stem cells (adult bone marrow vs 13-day fetal liver), do not necessarily play a significant role in the manifestation of H-2 restriction specificity and Ir phenotype of T cells generated in H-2 incompatible radiation chimeras.