The effects of pharmacologic agents on immune-complex-induced redistribution of B-lymphocyte Fc receptors

Characterization of B lymphocytes rescued from apoptosis by platelet-activating factor

B lymphocyte development is characterized by deletion via apoptosis of immature cells that are insufficiently stimulated. We have previously demonstrated that crosslinking of the B cell receptor (BCR) using anti-IgM antibodies (alphaIgM) (2 microg/ml) in Ramos B lymphoblastoid cells causes deletion of 30-40% of cells by apoptosis in 24 h. Addition of the potent lipid mediator platelet-activating factor (10(-7) M) to alphaIgM stimulated Ramos cells significantly decreases the number of apoptotic cells as measured by annexin V labeling. We have characterized the phenotype of Ramos cells that have not become apoptotic following BCR stimulation. In these cells, there is a significant decrease in the surface expression of the VLA-4 adhesion molecule (31% of control expression) and surface IgM expression (sIgM) (53% of control expression). Significantly fewer cells co-incubated with platelet-activating factor (PAF) underwent apoptosis, and the remaining cells maintained control levels of VLA-4 (104% of control expression) and sIgM expression (104% of control). All of these protective effects were inhibited by the specific PAF receptor antagonist, WEB 2170. The action of PAF on alphaIgM induced apoptosis was not inhibited by either cycloheximide or cytochalasin B, suggesting that de novo protein synthesis and F-actin polymerization were not implicated in the rescue of Ramos cells by PAF. In contrast, the ability of PAF to maintain sIgM and VLA-4 expression at control levels was inhibited by cycloheximide (7. 5 microg/ml). Cytochalasin B (5 microg/ml) had no effect on sIgM expression but blocked the decrease in VLA-4 expression mediated by alphaIgM. These data indicate that PAF's effect on rescuing and maintaining alphaIgM stimulated Ramos B cells is mediated via at least two pathways. Abrogation of apoptosis does not require de novo protein synthesis, while maintenance of sIgM and VLA-4 expression requires protein synthesis.

Inhibition of lymphocyte and monocyte antibody-dependent cellular cytotoxicity by immune complexes: effect of normal human serum

Antibody-dependent cellular cytotoxicity (ADCC) mediated by peripheral blood mononuclear cells (PBMC) and by isolated populations of lymphocytes and monocytes was compared for susceptibility to inhibition by soluble immune complexes (IC) and by heat-aggregated IgG (HAIgG). It was found that the decrease of ADCC was significantly higher in lymphocytes than in monocytes at all IC and HAIgG concentrations employed (P less than 0.001). The degree of inhibition of PBMC-mediated ADCC was similar to that observed in monocyte ADCC. In previous reports, we demonstrated that IC inhibition of PBMC-mediated ADCC could be reversed by normal human serum (NHS) used as a source of complement (C). In this paper, we study the effects of NHS on isolated populations of monocytes and lymphocytes. It was found that NHS was unable to modify the capacity of IC-blocked monocytes to mediate ADCC. On the contrary, NHS efficiently reversed the inhibition of both ADCC and Fc gamma R expression in IC-blocked lymphocytes. We propose that the regulation of Fc gamma R-IC interactions by C may constitute a physiological way to preserve Fc gamma R expression in lymphocytes.

Fc receptor--more answers, more questions

Fc receptors, belonging to the most important surface structures of a number of cells participating in the immune processes, have been intensely studied during the past decade. The present review summarizes the contemporary knowledge of the specificity and heterogeneity of Fc receptors and of factors influencing their expression, and includes some views on their function. In addition, it mentions their relationship to other cell surface structures, expression of Fc receptors during ontogeny of the organism and in certain diseases. Finally, data concerning the isolation and biochemical characterization of the Fc receptor molecule are presented.

Effect of colchicine derivatives on the antibody response induced in vitro

Effect of 44 colchicine derivatives on the induction of antibody response in tissue cultures was tested. Lymphatic cells from the spleen of BALB/c mice were cultivated with antigen (sheep red blood cells) and the number of antibody forming cells was determined by the plaque technique. Most compounds with the immunoinhibitory effect are derived from the colchicine formula (I). The effect was increased by introducing ethyl, formyl or methylenedioxide groups. Colchinols exerted very good immunoinhibitory effect resulting by contraction of tropolone ring C into the aromatic one. A complete loss of the effectivity was detected in the case of glucoside of colchicine, colchiceine, isocolchicine, oxycolchicine, allocolchicine and in lumiderivatives of colchicine. No correlations between the immunoinhibitory effect, toxicity and stathmokinetic effect were detected: decrease of cell viability and arrest of mitoses were not observed in cultured lymphocytes within the range of the immunoinhibitory effect. The effect of colchicine derivatives was manifested as the inhibition of lymphocyte blastogenesis, which is probably the result of membrane transport blockade.

Interactions between lymphocyte membrane molecules. I. Interaction between B lymphocyte surface IgM and Fc IgG receptors requires ligand occupancy of both receptors

The independent B lymphocyte surface membrane receptors IgM and Fc IgG receptors were evaluated for interactions using immunoflourescence. Ligand [F(ab')2 anti-mu]-induced capping of surface IgM resulted in capping of Fc IgG receptors only if the latter were occupied during the capping process by: (a) soluble antigen-antibody complexes that themselves provided insufficient cross-linking to result in capping; or (b) monomeric IgG at physiologic concentrations (or less) either purified or as normal serum. Ligand-induced capping of Fc IgG receptors did not result in capping of surface IgM occupied by monomeric F(ab') anti-mu. Control experiments showed that ligand binding to or capping of only one of these two receptors has no effect on the other, and that there were no cross-reactions. The interaction appears specific in that ligand-induced capping of surface IgM did not induce capping of ligand-occupied surface IgD or I-A antigens. Thus, there appears to be a specific interaction between ligand-bound surface IgM and ligand-bound Fc IgG receptors on the B lymphocyte surface. The results also indicate that binding of monomeric IgG produces a reversible alteration in the Fc IgG receptor leading to association with ligand-bound surface IgM. Because Fc IgG receptors are continuously exposed to monomeric IgG in vivo, these results suggest that whenever surface IgM is involved in a B lymphocyte response to an immunologic stimulus, the Fc IgG receptor is also involved.

Natural and antibody-dependent cellular cytotoxicity in tumour-adherent T lymphocytes: expression of Fc receptors and of a human T-subgroup-specific antigen

Adherence of human lymphocytes to allogeneic tumour cell monolayers was found to depend on the presence of monocytes. Adherent lymphocytes could be separated from tumour cells by treatment with lidocaine followed by nylon wool passage. Tumour-adherent cells (70% E-RFC, 45% Fc gamma-R, 23% Fc mu-R, 5% monocytes) exhibited enriched natural killer (NK) activity not only against the tumour cell line used for isolation but also against seven other targets. When T cells were isolated subsequently as E-rosettes by density gradient centrifugation through Percoll, the enrichment in cytotoxicity was even more pronounced. Tumour-adherent T cells were severalfold enriched in both NK and antibody-dependent cell-mediated cytotoxicity (ADCC) activity. However, this enrichment was not paralleled by a concomitant increase in the number of T gamma cells (tumour-adherent T cells: 17% T gamma, 40% T mu ; tumour-nonadherent T cells: 12% T gamma, 60% T mu). Marked differences could be observed by staining with a monoclonal antibody that was raised against human leukaemic T gamma cells of high NK and ADCC activity. This antibody (T 8-11) stained 60% of tumour-adherent T cells, 20% of nonadherent T cells and 29% of T-cell controls. These results indicate that the spontaneous cytotoxic activity of human T cells resides within a small population, most of which are characterized by a specific surface antigen but not by conventional Fc gamma receptors.