T cell-dependent induction of NF-kappa B in B cells.

In comparison to B cell stimulation mediated by surface immunoglobulin (Ig) antigen receptor ligation, little is known about the intracellular events associated with T cell-dependent B cell responses. A model for the efferent phase of T cell-B cell interaction was used to examine the capacity of activated T cells to trigger nuclear expression of the trans-acting transcription factor, NF-kappa B, in B cells. Fixed, activated, but not fixed, resting Th2 cells were found to induce increased binding activity for a kappa B site-containing oligonucleotide in a time-dependent manner. This induction of NF-kappa B was eliminated by an antibody directed against a 39-kD cell interaction protein on activated T cells as well as by a soluble form of B cell CD40. Of particular relevance to intracellular signaling, NF-kappa B induction was not diminished by prior depletion of B cell protein kinase C (PKC) with phorbol myristate acetate. These results strongly suggest that T cell-dependent B cell stimulation is associated with NF-kappa B induction via p39-CD40 interaction and that this is brought about by non-PKC dependent signaling, in marked contrast to the previously documented requirement for PKC in sIg receptor-mediated stimulation. This suggest that NF-kappa B responds to more than one receptor-mediated intracellular signaling pathway in B cells and may be part of a "final common pathway" for B cell stimulation.

ELISA for the detection of anticardiolipin antibodies. High specificity based on the use of adult bovine serum as buffer and systematic subtraction of non-specific binding.

We have used an ELISA procedure to compare the reactivity of samples with or without IgG anticardiolipin antibodies (ACA) on cardiolipin-coated wells (target wells) and cardiolipin-free wells (control wells), using 10% fetal calf serum (10% FCS), 10% adult bovine serum (10% ABS) or 1% bovine serum albumin (1% BSA) as buffer. With 1% BSA, ACA reactivity was very low which suggests that this buffer would be inappropriate for use in ELISA procedures for ACA. 10% FCS induced non-specific binding of normal IgG only on target wells, particularly in the case of IgG hypergammaglobulinemia. With 10% ABS, this non-specific binding occurred on the solid phase with and without cardiolipin and could be accurately evaluated by subtracting the absorbance of control wells. Results of assays on 35 systemic lupus erythematosus sera using 10% ABS as buffer showed that highly specific results-could be obtained only if non-specific binding was systematically subtracted.

Lipid and protein components of the syncytiotrophoblast plasma membrane inhibit lymphocyte proliferation by two distinct pathways.

The ability of syncytiotrophoblast plasma membrane lipid and protein fractions (STPM lipids, STPM proteins), tested under a reconstituted form, to inhibit lymphocyte proliferation induced by PHA was investigated. The cytostatic activity of STPM proteins appeared greater than that of the STPM lipids. Furthermore, IL-2 production and IL-2 receptor expression by activated lymphocytes were markedly decreased in the presence of STPM proteins compared to the native membrane but remained unaffected in the presence of STPM lipids. Finally, the inhibition of lymphoproliferation could be maintained after removal of the protein fraction from lymphocytes prior to stimulation by PHA. The biological and immunological significance of these results is discussed.

The inhibitory effect of human syncytiotrophoblast plasma membrane vesicles on in vitro lymphocyte proliferation is associated with reduced interleukin 2 receptor expression.

The mechanisms by which vesicles of syncytiotrophoblast plasma membranes (STPM) prepared from full-term human placentas inhibit lymphocyte proliferation have been investigated. In the presence of STPM, IL-2 secretion and the expression of protein P55 (IL-2R P55) from its receptor were examined in two models of PBMC proliferation: induced by PHA in 3-day-old cultures, and induced by IL-2 in 6-day-old cultures. In the case of PHA stimulation, STPM strongly inhibited IL-2 (but not IL-1) secretion and IL-2R P55 expression at a concentration where lymphocyte proliferation was also blocked. In these conditions, the addition of excess recombinant IL-2 (rIL-2) only partially restored proliferation and IL-2R P55 expression. In addition, STPM inhibited proliferation and IL-2R P55 expression when resting PBMC were stimulated by a high concentration of rIL-2. These results suggest that STPM inhibit lymphocyte proliferation by affecting one or several events occurring in the synthesis and/or expression of IL-2R P55 by a mechanism which is at least partially independent of its inhibitory effect on IL-2 secretion. The significance of these results is discussed in the context of the survival of the fetal allograft.

Inhibitory effect of human syncytiotrophoblast plasma membrane vesicles on Jurkat cells activated by phorbol ester and calcium ionophore.

The effects of syncytiotrophoblast plasma membrane vesicles (STPM) on stimulated Jurkat leukemic T cells have been investigated. STPM inhibited IL-2 production and the expression of protein P55 of the IL-2 receptor (IL-2R P55), when Jurkat cells were stimulated by a combination of calcium ionophore A23187 (CaI) + phorbol 12-myristate 13-acetate (PMA). STPM also inhibited IL-2R P55 when cells were stimulated by PMA alone, a situation in which IL-2 production is negligible. On the other hand, STPM had no effect on the sustained mobilization of intracellular Ca2+ induced by CaI nor on the PKC-dependent CD3 down regulation induced by PMA. Finally STPM had no effect on intracellular cAMP levels. These results show that (i) the inhibitory effect of STPM on IL-2R P55 expression is independent of the inhibition of IL-2 production, and (ii) the inhibitory effects of STPM are at least partially independent of phosphatidylinositol 4,5-bisphosphate hydrolysis. They suggest that STPM affect a signaling pathway activated by PMA but possibly PKC independent.

Inhibition of induced lymphocyte proliferation by lipid and protein components of the syncytiotrophoblast plasma membrane.

PROBLEM: The aim of this work was to define the respective responsibilities of the lipid and protein components of syncytiotrophoblast plasma membranes on the inhibition of lymphocyte proliferation induced in vitro. METHOD: A fractionation method using octyl-beta-D-glucopyranoside enabled lipoprotein, lipid, and protein fractions to be isolated from the membrane. RESULTS: The lipid fraction was shown nonspecifically to inhibit lymphocyte proliferation, to a lower extent compared with the native membrane. Alternatively, the protein fraction used as a proteoliposome contained the totality of the cytostatic effect of the native fraction. CONCLUSION: These results are discussed generally in the context of the immunoregulatory role of membrane lipids and proteins and in relation to the local properties of syncytiotrophoblast plasma membrane components in fetal graft tolerance.