Active Suppression of B Lymphocyte Maturation by Two Different Newborn T Lymphocyte Subsets

Abstract

Leukocytes from newborns and pregnant women were shown to be unable to mature into plasma cells in cultures stimulated by pokeweed mitogen (PWM). This is in contrast with the generation of IgM, IgG, and IgA-containing cells constantly observed in adult leukocytes. This defective B cell maturation was due to an active suppression mediated by T lymphocytes. T lymphocytes bearing receptors for IgG (Tγ) and Tγ-depleted populations were both able to exert this effect. Tγ lymphocytes inhibited B cell maturation without significantly affecting T and B cell proliferation, and their effect persisted after an incubation of 18 hr at 37°C. Tγ-depleted lymphocytes suppressed lymphocyte proliferation and, subsequently, B cell maturation into plasma cells. The suppressor activity of this second cell type was markedly diminished after incubation. Co-culture experiments showed that PWM-induced newborn suppressor T lymphocytes suppressed maturation of adult B cells only when T lymphocytes were present, suggesting that suppressor cells acted upon a target T cell population rather than directly upon B cells. Indirect inhibition of B cell maturation resulted in a lack of appearance of membrane IgG and IgA expression, although proliferation and loss of membrane IgD were observed. Although similar suppressor effects can be induced in vitro in adult leukocytes by fixation of immune complexes on Tγ populations or after concanavalin A activation of Tγ-depleted populations, the peculiarity of the perinatal period appears to be the spontaneous activation of the two types of T suppressor lymphocytes.