SUPPRESSION OF PLASMA CELL DIFFERENTIATION BY PRIMED T LYMPHOCYTES

Abstract

Cord blood T lymphocytes inhibit the division of maternal T cells and can block plasma cell (PC) differentiation of unrelated B cells induced by pokeweed mitogen (PWM). These effects are variable in degree but could be important in regulating immune responses between mother and fetus. Contact with maternal HLA antigens not shared by the fetus is one possible stimulus to such suppression. This was investigated by using adult blood T lymphocytes since these are not normally suppressive but can be stimulated in one-way mixed lymphocyte culture (MLC). In 4 experiments, when 40,000 T cells harvested from control (X × X) cultures were added to autologous (donor X) PWM stimulated cultures the mean number of PC (x10⁻³) per culture was 32.2, IgM and 17.2, IgG. The number fell to 6.3 IgM and 4.6 IgG (mean suppression 78%) when the added T cells had been primed in MLC (X × Y) to the cells tested for differentiation (donor Y). There was slight reduction in the numbers of PC obtained in cultures of lymphocytes from the same source as the primed T cells (X × Y added to X), giving a mean suppression of 35%, and a comparable reduction in the response of an unrelated control (X × Y added to Z). The results suggest that specific suppression, which might be mediated by cytotoxic cells, is of greater magnitude than non-specific suppression. They are compatible with the view that a histocompatibility stimulus to the fetus could induce the suppressive characteristics of human cord blood T lymphocytes. (Grant 1-354 from the National Foundation, March of Dimes)

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