DEVELOPMENT OF IMMUNOSUPPRESSOR CELLS

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Abstract
The suppressive activity of neonatal liver cells was studied using in vitro and in vivo experimental models of cell-mediated immunity. Native liver cells could exert a nonstrain-specific suppressive effect, as measured in vitro in the mixed lymphocyte culture reaction. In the in vivo system, which consisted of the assay of mortality of sublethally irradiated (C3H/eb .times. C57BL/6)F1 mice challenged with parental C57BL spleen cells, the mice died within 100 days of spleen injection. However, when the spleen cells were injected in a mixture with parental (C57BL) liver cells, there was no mortality. Prevention of graft-vs.-host response by liver cells was strain specific and was manifested only in systems where spleen cells were syngeneic to the liver cells used, but not when spleen and liver cells were unrelated. The suppressive effect of the liver in vivo was found to depend on thymic function, since no suppression of graft-vs.-host response by liver cells could be detected in thymectomized irradiated hosts. Preincubation of these liver cells with thymic hormone, before administration to the thymectomized hosts in a mixture with spleen cells, led to manifestation of the suppressive capacity. Suppressor cells seem to be present in the neonatal liver, and they subsequently undergo an additional phase of maturation that enables their further maintenance in vivo and the specific expression of their suppressive function in the irradiated recipient. Simultaneously, it is suggested that presence of antigen and thymic function may be critical in directing the pattern of differentiation of liver-specific suppressors.