Concanavalin A induced and spontaneous suppressor cell capacity of newborn and fetal lamb lymphocytes

Concanavalin A induced newborn lamb blood lymphocytes suppress the proliferation of adult lymphocytes to the same magnitude as similarly induced adult suppressor cells. Concanavalin A induced suppressor capacity of fetal spleen cells at term is not as strong as that of newborn peripheral blood lymphocytes. Thymocytes of the same fetuses do not possess any suppressive capacity inducible by this mitogen, but show a spontaneous suppressor capability. Spleen cells exhibit only a low spontaneous activity. Interestingly, when peripheral blood lymphocytes of newborn lambs spontaneously suppress the response of both unrelated and maternal cells, adult lymphocytes enhance the proliferation. These results show that functional suppressor cells are found in both newborn and fetal lambs. Our data also indicate that cells spontaneously suppressive are established in thymus and spleen, whereas cells that can be rendered suppressive by concanavalin A stimulation are found in the spleen. Therefore, the spontaneous thymic suppressor cells may represent a more primitive cell population than those of the spleen.