Functional studies on MEL-14+ and MEL-14- T cells in peripheral lymphoid tissues.

Functions of MEL-14+ T cells and MEL-14- T cells in peripheral lymphoid tissues were analyzed and compared. The MEL-14- T cells, representing a minor subpopulation of spleen and lymph node T cells, generated considerably higher mixed lymphocyte reaction and mitogen responses than the MEL-14+ T cells in any lymphoid tissues studied. Furthermore, upon stimulation with ConA the MEL-14- CD8+ T cells produced significantly larger amounts of IL-2 and IFN-gamma than MEL-14+ CD8+ T cells did. A similar but less marked observation was obtained with the CD4+ T cell population. Furthermore, when B10.BR mice were immunized with AKR (Mls-1a) spleen cells, the proportion of the Mls-1a reactive V beta 6+ T cells from draining lymph nodes increased and a substantial proportion of the increasing V beta 6+ T cells was shown to be MEL-14-. The present findings on the whole indicate that MEL-14- T cells in the peripheral lymphoid tissues are at functionally high levels and may represent memory cells which have been previously stimulated in vivo.

Production of minor lymphocyte stimulatory-1a antigen from activated CD4+ or CD8+ T cells.

Minor lymphocyte stimulatory (Mls) Ag are super Ag that stimulate a high proportion of T cells of a specific TCR V beta family. One of the super Ag, Mls-1a, which is recognized mainly by TCR V beta 6+ and V beta 8.1+ T cells, has recently been linked to the response to product of the open reading frame in 3'-long terminal repeat of endogenous mammary tumor virus, MTV-7. It is quite certain that B cells are able to produce and also to present the Mls-1a Ag. However, it remains to be determined whether other cell types, especially T cells, produce Mls-1a Ag. In this study using highly purified T cell subpopulations, capacity to produce Mls-1a Ag was analyzed by calculating the proportion of Mls-1a reactive V beta 6+ or V beta 8.1+ T cells in responding cell populations. We found that nonstimulated CD8+ T cells produced a low amount of Mls-1a Ag, and the capacity to do so was considerably increased by stimulation with immobilized anti-TCR mAb. By contrast, nonstimulated CD4+ T cells did not produce Mls-1a Ag at all. Even when CD4+ T cells were activated via TCR signaling with immobilized anti-TCR mAb, CD4+ T cells did not produce Mls-1a Ag. However, CD4+ T cells primed with conventional Ag in vivo produced Mls-1a Ag on restimulation with that specific Ag in vitro. These findings indicate that not only CD8+ T cells but also CD4+ T cells can produce Mls-1a Ag on appropriate stimulation, although different mechanisms for Mls-1a production may operate between the CD4+ and CD8+ T cells.

Reconstitution of lymphoid tissues under the influence of a subclinical level of graft versus host reaction induced by bone marrow T cells or splenic T cell subsets.

Reconstitution of lymphoid tissues under the influence of subclinical graft versus host reaction (GVHR) has been investigated. Lethally irradiated AKR mice were reconstituted with B10 bone marrow (BM) cells which had been treated with anti-Thy-1 antibody alone without complement (GVHR chimera). Their immunological reconstitution was analyzed and compared with that of AKR recipients which had been reconstituted with B10 BM cells treated with anti-Thy-1 antibody plus complement (control chimera). One hundred percent of both chimeras survived more than 100 days without showing clinical signs of GVHR. However, full donor chimerism was accomplished at an early stage after reconstitution in the former GVHR chimeras, whereas a substantial number of recipient T cells persisted in control chimeras for the entire observation period. When reconstitution of various lymphoid tissues was compared between control and GVHR chimeras, no difference in the reconstitution of the thymus and spleen was noted. By contrast, the cellularity of peripheral lymph nodes in GVHR chimeras was regularly considerably lower than that of the control chimeras. The apparent insufficiency of lymph node reconstitution appeared to be attributable to the impairment of lymph node structure itself which may be involved in lymphocyte homing. Furthermore, clonal deletion of V beta 6+ T cells which are reactive to recipient (Mls-1a) antigens was abrogated in the GVHR chimeras but was normally induced in the more completely T cell-depleted control chimeras. This abrogation of clonal deletion of V beta 6+ T cells appeared to result from the early disappearance of recipient T cells in these chimeras. Thus, it appeared that donor T cells in the BM that survive anti-Thy-1 treatment in vitro plus subsequent BM transplantation induced a subclinical level GVHR which contributed to the full donor chimerism as well as abrogation of clonal elimination of V beta 6+ donor T cells. Indeed, inoculation of CD8+ T cells along with the transplantation of the T cell-depleted BM cells (anti-Thy-1 plus C-treated cells) from donor mice into the AKR recipients was also shown to induce a similar state in the recipients.

Lymphokine-activated killer cell activity of CD4-CD8- TCR alpha beta + thymocytes.

Functions of CD4-8-TCR alpha beta+ thymocytes, which are characterized by predominant usage of V beta 8.2 TCR, have remained unclear. In this study, we found that the CD4-8-TCR alpha beta + thymocytes expressed NK1.1 Ag and IL-2R beta-chain but not IL-2R alpha-chain. When the CD4-8- TCR alpha beta + thymocytes were cultured in the presence of IL-2, the CD4-8-TCR alpha beta + thymocytes vigorously proliferated. After 7 days of culture in the presence of 1000 U/ml of IL-2, approximately half of the CD4-8-TCR alpha beta + thymocytes lost NK1.1 Ag. However, the remaining half of the CD4-8-TCR alpha beta + cells showed increasing levels of NK1.1 Ag and acquired killer activity against tumor cells such as YAC-1, P815, and EL-4. These cells also killed syngeneic as well as allogeneic thymocytes. The LAK activity by the NK1.1+ CD4-8-TCR alpha beta + thymocytes was not inhibited by anti-NK1.1, anti-TCR alpha beta, or anti-CD44 mAb but was partially inhibited by anti-LFA-1 mAb. These findings indicate that the CD4-8-TCR alpha beta + thymocyte population can be divided into two population on the basis of NK1.1 expression after culture in the presence of IL-2. The NK1.1 Ag expression on the cultured CD4-8-TCR alpha beta + seems to be correlated to acquisition of LAK activity, although the NK1.1 Ag itself may not be directly involved in the target cell recognition. The present data suggest that the CD4-8- TCR alpha beta + thymocyte population is a functional T cell lineage which may serve as cells of immune defense and/or immune regulation.

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.