Characterization of gp39, a B-lymphocyte associated differentiation antigen which is also present on granulocytes and macrophages

The role of CD154 in organ transplant rejection and acceptance

CD154 plays a critical role in determining the outcome of a transplanted organ. This simple statement is amply supported by experimental evidence demonstrating that anti-CD154 antibodies are potent inhibitors of allograft rejection in many rigorous transplant models. Unfortunately, despite intensive investigation over the past ten years, the precise mechanisms by which antibodies against CD154 exert their anti-rejection effects have remained less obvious. Though originally classified with reference to B-cell function, CD154-CD40 interactions have also been shown to be important in T cell-antigen-presenting cell interactions. Accordingly, CD154 has been classified as a T-cell co-stimulatory molecule. However, mounting data suggest that treatment with anti-CD154 antibodies does not simply block costimulatory signals, but rather that the antibodies appear to induce signalling in receptor-bearing T cells. Other data suggest that anti-CD154 effects may be mediated by endothelial cells and possibly even platelets. In fact, the current literature suggests that CD154 can either stimulate or attenuate an immune response, depending upon the model system under study. CD154 has secured a fundamental place in transplant biology and general immunology that will no doubt be the source of considerable investigation and therapeutic manipulation in the coming decade.

Monocytoid B-cell lymphoma: a study of 36 cases

We have studied 36 cases of monocytoid B-cell lymphoma (MBCL). We confirm the predilection for females (30 of 36; ratio, five women to one man). The median age was 65 years (range, 29 to 85 years). Monocytoid B-cell lymphoma characteristically involves peripheral lymph nodes (30 of 36) with a propensity for paraparotid or intraparotid nodes. Salivary glands were affected in five patients. Other extranodal sites of involvement included breast, thyroid, stomach, and soft tissue of chest wall. Eight patients manifested with Sjögren's syndrome, one had systemic lupus erythematosus, one presented initially with Raynaud's phenomenon, and two had a monoclonal gammopathy. "Composite lymphomas" were encountered in seven patients. In addition, association with or progression to a higher-grade lymphoma, ie, mixed small and large cell (one) and large cell (six), was observed in seven patients and was associated with a more aggressive behavior of the lymphoma. Immunohistochemical studies performed on biopsy sections from 20 patients confirmed the B-cell nature of MBCL. An average reactivity of less than 10% of the monocytoid B cells with the proliferation marker Ki-67 was demonstrated, in keeping with the indolent behavior of MBCL. Despite our observation of follicular lymphomas frequently accompanying MBCL, the t(14;18) chromosomal translocation does not appear to play a pathogenetic role for MBCL, as determined by molecular studies for the t(14;18) chromosomal translocation and immunologic studies for the BCL2 protein. Our observations also provide support for the proposal that there is an overlap between MBCL and "MALT lymphomas" (those arising from mucosa-associated lymphoid tissue).

Cross-linking of both types of IgG Fc receptors, Fc gamma RI and Fc gamma RII, enhances intracellular free Ca2+ in the monocytic cell line U937

We have studied the effects of Fc receptor triggering on the free cytosolic Ca2+ concentration, [Ca2+]i, in U937. These cells express two types of IgG Fc receptors, Fc gamma RI and Fc gamma RII. Binding of several anti-Fc gamma RI and anti-Fc gamma RII mouse monoclonal antibodies (MoAb) to Quin2- or Indo-1-loaded U937 cells had no direct effect on [Ca2+]i. After addition of a bridging anti-mouse Ig antibody however, transient increases in [Ca2+]i were observed for both types of Fc gamma R. One of the anti-Fc gamma RII MoAb, CIKM5, was exceptional in that it could induce Ca2+ increases in U937 cells by itself. Studies with F(ab')2 fragments of CIKM5 revealed that this MoAb simultaneously binds to Fc gamma RII, via both its Fab and Fc fragments, which might induce cross-linking of two Fc gamma RII molecules. One anti-Fc gamma RI MoAb, 197, a mouse (m)IgG2a antibody directed to an epitope outside the IgG-binding region, remarkably also caused an immediate increase in [Ca2+]i, but only when added to U937 precultured with gamma interferon (IFN-gamma). Fc gamma RI can bind monomeric human IgG as well as mIgG2a, and cross-linking of cytophilic Ig induced an increase in [Ca2+]i. Our results show that [Ca2+]i increases can be induced only after cross-linking of Fc gamma R, either via anti-Fc gamma R MoAb or via Fc-FcR interactions. Furthermore, we show that Fc gamma R cross-linking results in activation of the Ca2+/phosphatidylinositol (PI) signal transduction pathway.

Comparison of the 40 kDa hematopoietic cell antigens bound by monoclonal antibodies IV.3, 41H.16 and KB61

A study is presented which compares the properties of antigens with relative mol. mass of about 40,000, detected by three different monoclonal antibodies: IV.3, 41H.16 and KB61. Antibody IV.3 has been shown (in work by other investigators) to detect the Fc receptor for IgG. It recognizes this molecule on neutrophils, macrophages and platelets. Antibody 41H.16 precipitates a molecule of mol. wt of approximately 40,000, which is present on B cells, neutrophils and macrophages. The antigens precipitated by IV.3 and 41H.16 have been compared by isoelectric focusing, sequential antibody-mediated affinity chromatography and trypsin hydrolysis. The results indicate that these two antibodies bind different molecules of similar relative mol. mass. A third antibody, KB61, has been reported, which also reacts with a 40,000 mol. wt molecule and has a distribution of cellular reactivity which is similar to 41H.16. Sequential preclearing experiments have shown that these molecules recognize the same antigen.