Bingyan Wang

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 Vβ6+ 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 Vβ6+ T cells reactive to the recipient Ag (Mls‐1a) was abolished in T+ chimeras but successfully induced in T– chimeras. The Vβ6+ 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 Vβ17a+ 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.

Sequential Analysis of Distributions of Donor‐derived Thymocytes Bearing T‐cell Antigen Receptor (TCR) and Donor‐derived la+ 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 Vβ8 molecules was investigated. The donor‐derived la+ cells appeared in the medulla on day 7 after reconstitution. The la+ 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 Vβ8+ thymocytes were first recognized in the cortex on day 10 and were identifiable in the medulla by day 14. The Vβ8+ cells seemed to be mainly CD4+8+ double‐positive. Furthermore, most of the Vg8’cells in the medulla of chimeras given cyclosporin A for 3 weeks after reconstitution appeared to be CD4+8+. The present findings demonstrate that CD4 8+ thymocytes which bear a low concentration of TCR exist in the thymic medulla at a relatively early stage when donor‐derived la+ cells have already settled there. The coincidental appearance and coexistence of la+ cells and TCR+ thymocytes in the medulla suggest that these histological characteristics may be related to the selection of thymocytes in this area.