Identification and characterization of the BCG cell wall-stimulated suppressor cells in inbred rats.

In vitro experiments were undertaken to investigate the effect of intraperitoneal (i.p.) inoculation of BCG cell walls attached to oil droplets (BCGcw) on mitogenic and alloantigenic responses of spleen and bone marrow cells. These in vitro studies demonstrated that: (1) spleen cells from BCGcw-immunized ACI rats had decreased responsiveness to Concanavalin A (Con A) and to alloantigenic stimulation, (2) depressed Con A reactivity could also be induced in Buffalo rat spleen cells by the i.p. inoculation of BCGcw, (3) normal ACI rats had suppressor cells in their bone marrow but not in their spleens, (4) BCGcw-immunized ACI rats demonstrated an increase in the suppressive activity of their bone marrow as early as 1 day after inoculation of BCGcw, while suppressor activity was found in the spleen as early as 2 days after BCGcw inoculation, (5) characterization of the BCGcw-induced splenic suppressor cell demonstrated it to be adherent to plastic or nylon wool, radiation-resistant, and removed by treatment with carbonyl iron. These properties were consistent with the identification of the suppressor cell as a macrophage, (6) the Con A and mixed lymphocyte reactivities of normal spleen cells could be suppressed by the addition of the adherent spleen cell population from BCGcw-immunized ACI rats, and (7) the adherent suppressor cells from BCGcw-immunized rats suppressed Con A reactivity across a major histocompatability barrier.