Liliana Calosso

Human CD38: a glycoprotein in search of a function.

The human CD38 molecule appears to mediate several diverse activities, including signal transduction, cell adhesion and cyclic ADP-ribose synthesis. In this article, the authors consolidate the information available on this highly interesting, multifunctional protein.

CD38 expression and functional activities are up-regulated by IFN-γ on human monocytes and monocytic cell lines

Human CD38, a surface molecule expressed by immature and activated T and B lymphocytes, has been characterized as a molecule transducing activation and proliferation signals, and intervening in adhesion to endothelium via its ligand CD31. CD38 is also a complex ectoenzyme featuring ADP‐ribosyl cyclase/cyclic ADP‐ribose hydrolase activities, leading to the synthesis and degradation of cADPR, a Ca+‐mobilizing agent. We investigated the effects of monocyte‐activating stimuli (IFN‐γ, IL‐2, LPS, TNF‐α, and GM‐CSF) on the expression and function of CD38, starting from the observation that human monocytes and the derived lines U937, THP‐1, and Mono‐Mac‐6 bear the molecule on their surface. Our results indicate that IFN‐γ is a strong up‐modulator of CD38, and IL‐2 increases its expression only modestly. LPS, TNF‐α, and GM‐CSF had no detectable effects. Treatment with IFN‐γ produced a dose‐ and time‐dependent up‐regulation of CD38 in monocytes and monocytic lines, which was paralleled by increased ADP‐ribosyl cyclase/cyclic ADP‐ribose hydrolase activities. Furthermore, CD38 ligation by specific MoAb reduced the IFN‐γ‐dependent enhancement of monocyte‐dynamic adhesion to endothelial monolayers. These findings identify IFN‐γ as a modulator of monocytic CD38 expression and indicate that CD38 plays a specific role in the activation and adhesion processes performed by monocytes.

Human CD38 interferes with HIV-1 fusion through a sequence homologous to the V3 loop of the viral envelope glycoprotein gp120.

CD38 is a progression marker in HIV‐1 infection, it displays lateral association with CD4, and down‐modulates gp120/CD4 binding. The aim of this study was to elucidate the mechanism behind the interplay between CD4, CD38, and HIV‐1. We used mouse cell transfectants expressing human CD4 and either CD38 or other CD4‐associated molecules to show that CD38 specifically inhibits gp120/CD4 binding. Human cell transfectants expressing truncated forms of CD38 and bioinformatic analysis were used to map the anti‐HIV activity and show that it is concentrated in the membrane‐proximal region. This region displayed significant sequence‐similarity with the V3 loop of the HIV‐1 gp120 glycoprotein. In line with this similarity, synthetic soluble peptides derived from this region reproduced the anti‐HIV effects of full‐length CD38 and inhibited HIV‐1 and HIV‐2 primary isolates from different subtypes and with different coreceptor use. A multiple‐branched peptide construct presenting part of the sequence of the V3‐like region potently and selectively inhibited HIV‐1 replication in the nanomolar range. Conversely, a deletion in the V3‐like region abrogated the anti‐HIV‐1 activity of CD38 and its lateral association with CD4. These findings may provide new insights into the early events of HIV‐1 fusion and strategies to intervene.

Effects of the human CD38 glycoprotein on the early stages of the HIV-1 replication cycle

CD38 displays lateral association with the HIV‐1 receptor CD4. This association is potentiated by the HIV‐1 envelope glycoprotein gp120. The aim of this work was to evaluate the CD38 role in T cell susceptibility to HIV‐1 infection. Using laboratory X4 HIV‐1 strains and X4 and X4/R5 primary isolates, we found that CD38 expression was negatively correlated to cell susceptibility to infection, evaluated as percentage of infected cells, release of HIV p24 in the supernatants, and cytopathogenicity. This correlation was at first suggested by results obtained in a panel of human CD4+ T cell lines expressing different CD38 levels (MT‐4, MT‐2, C8166, CEMx174, Supt‐1, and H9) and then demonstrated using CD38 transfectants of MT‐4 cells (the line with the lowest CD38 expression). To address whether CD38 affected viral binding, we used mouse T cells that are non‐permissive for productive infection. Gene transfection in mouse SR.D10.CD4~.F1 T cells produced four lines expressing human CD4 and/or CD38. Ability of CD4+CD38+ cells to bind HIV‐1 or purified recombinant gp120 was significantly lower than that of CD4+CD38~ cells. These data suggest that CD38 expression inhibits lymphocyte susceptibility to HIV infection, probably by inhibiting gp120/CD4‐dependent viral binding to target cells.—Savarino, A., Bottarel, F., Calosso, L., Feito, M. J., Bensi, T., Bragardo, M., Rojo, J. M., Pugliese, A., Abbate, I., Capobianchi, M. R., Dianzani, F., Malavasi, F., and Dianzani, U. Effects of the human CD38 glycoprotein on the early stages of the HIV‐1 replication cycle. FASEB J. 13, 2265–2276 (1999)

Histogenic characterization of the cells forming RA pannus

OBJECTIVE This work aims to clarify the histogenesis of the cells forming RA pannus: the pannocytes. METHODS 15 patients with seropositive RA; 5 controls with post-traumatic knee effusion and 5 with OA knee effusion were included in the study. Synovial tissues and fluids, collected during diagnostic arthrocentesis, were used as a source of cells to be cultured. Viable staining and cytocentrifugation were performed. Cell phenotype was investigated by immunofluorescence assays after different culture periods. Cells were also studied by immunohistochemistry to determine the presence of CD5, CD68:KP-1, CD68:PG-M1, vimentin, cytokeratin, a-SM-Actin. RESULTS Cells derived from RA samples were sub-divided into two population of lymphocyte-like and macrophage-like cells. Phenotypical characteristics of the first one were analysed after 6 days of culture and suggested they were T lymphocytes. The other population could grow in vitro for undefined time resembling the neoplastic-like proliferation previously described for pannocytes. Phenotypic characterization excluded that these cells were lymphocytes, monocyte-macrophages, fibroblasts, myofibroblasts, endothelial cells or keratinocytes. On the contrary, immunohistochemistry demonstrated that 100% of pannocytes were vimentin positive and 75% of these cells expressed also CD68:KP-1. CONCLUSIONS. The results exclude that pannocytes originate from monocyte-macrophages or from fibroblasts, but strongly support the hypothesis that they belong to the family of primitive embryonal connective tissue-forming cells (residue of the primitive mesenchymal tissue).