[Alloreactivity and mitogen-induced responses in allogeneic murine bone marrow chimeras].

Alloreactive mixed lymphocyte reaction (MLR), mitogen-induced response (MR), and suppressor cells against these responses in murine bone marrow chimeras were examined, to clarify the mechanisms of immunological tolerance and immunodeficiency after bone marrow transplantation (BMT). Between 35 and 70 days after BMT, there was no response of spleen cells from allogeneic chimeras against host (C3H/He) and donor (BALB/c) cells, although responses against third party (C57BL/6) cells were detected, thus indicating that these allogeneic chimeras were immunologically tolerant. The activity of suppressor cells against alloreactive responses was increased 35 to 55 days after BMT, so that these suppressor cells appeared to be related to immunological tolerance. Some of the suppressor cells against alloreactive responses were Thy1+. Among them some were Lyt1+ or Lyt2+, and others were Lyt1+2+. Plastic dish non-adherent cells had slightly weaker suppressor activity than adherent cells. Proliferative responses to Con A, PHA, and PWM were decreased 13 to 15 days after BMT, and gradually increased. The responses to LPS differed from those to the former three mitogens, showing an enhanced response 21 to 25 days after BMT. The increased response to LPS did not appear to be simply due to the increased number of non-T cells in the spleen of allogeneic chimeras. The alloantigen specific suppressor cells may play an important role in the induction and maintenance of immunological tolerance, while the alloantigen nonspecific suppressor cells and suppressor cells against MRs may be related to immunodeficiency after BMT.