Differential regulation of CXCR4 and CCR5 expression by interleukin (IL)-4 and IL-13 is associated with inhibition of chemotaxis and human immunodeficiency Virus (HIV) type 1 replication but not HIV entry into human monocytes.

Chemokine receptors CXCR4 and CCR5 play a key role in Human Immunodeficiency Virus (HIV) entry into CD4+ monocytic cells. Alteration in the expression levels of these receptors by immunoregulatory cytokines may influence viral entry and hence susceptibility to HIV infection, viral tropism, and disease progression. Helper T cell type 2 (Th2) cytokines interleukin (IL)-4 and IL-13, which share a subunit of their receptor components and exhibit similar biological effects, have been shown to play a key role in HIV infection and disease progression. In this study, we investigated the effects of IL-4 and IL-13 on the expression of CXCR4 and CCR5, and the biological implications of alteration of CXCR4 and CCR5 regulation on monocytic cells with respect to their migration in response to chemokines, HIV entry, and its replication. The results suggest that both IL-4 and IL-13 inhibited the expression of CXCR4, in contrast to CCR5, which was inhibited by IL-13 alone. The downregulation of CXCR4 and CCR5 was correspondingly associated with the inhibition of their respective ligand-induced chemotaxis. Although IL-13 inhibited the expression of both CXCR4 and CCR5, this downregulation of chemokine receptor expression was not sufficient to prevent virus entry. Furthermore, both IL-4 and IL-13 inhibited viral replication in monocytic cells, suggesting that inhibition of chemokine receptor expression per se by these cytokines may not be sufficient to prevent virus entry, and indicating these cytokines may be inhibiting viral replication by targeting pathways subsequent to virus entry.

Monocyte-derived IL12, CD86 (B7-2) and CD40L expression in relapsing and progressive multiple sclerosis.

Multiple sclerosis has been postulated to be an autoimmune disease in which Th1 immune responses predominate. This response is associated with an increased production of IFNgamma and IL12 produced by T cells and by cells of the monocyte (MO) lineage, respectively. An increased expression of costimulatory molecules by T cells and antigen-presenting cells is also observed. We hypothesized that in relapsing-remitting MS (RRMS) (with or without of IFNbeta treatment) and in secondary progressive patients (SPMS) IL12 and costimulatory molecules (CD80 [B7-1], CD86 [B7-2], CD28, CD40, CD40L) would be differentially produced or expressed by MO or T cells. We performed cross-sectional and longitudinal flow cytometric studies (at monthly intervals) on peripheral blood mononuclear cells (PBMC) or on MO from SPMS or untreated and IFNbeta-treated patients with RRMS. We determined that CD86 and CD40L expression was highest on MO derived from SPMS patients compared to those from RRMS or from healthy controls (HC). In vitro culture of PBMC with recombinant human IL10, a cytokine that may be increased in response to treatment with IFNbeta and that down-regulates CD86 expression, reduced the expression of CD86 on MO derived from RRMS patients to a much higher degree compared to cells derived from SPMS or HC. In vitro secreted IL12 levels from freshly isolated MO from SPMS patients were more than 10-fold higher than either the treated or the untreated RRMS or HC. RRMS patients treated with IFNbeta demonstrated slightly lower levels of MO IL12 secretion. Our data suggest that a key mechanism in the pathogenesis of MS is the increased expression of CD86 and CD40L and the increased production of IL12 during disease progression. Part of the mechanism of action of IFNbeta may be to reduce MO CD86 and CD40L expression and IL12 secretion; failure to do so might signify either a lack of response or a transition to a more progressive phase of illness.

CD4 is active as a signaling molecule on the human monocytic cell line Thp-1.

CD4 is a 56-kDa membrane glycoprotein expressed by a subset of T cells, by cells of the monocyte/macrophage lineage, and by eosinophils and dendritic cells. CD4 serves as a coreceptor for HIV and IL-16. T cell CD4 mediates signal transduction by associating with the protein tyrosine kinase p56(lck); this interaction does not exist in monocytes. We wished to elucidate the mechanism(s) by which monocyte CD4 transduces signals. Stimulation of CD4 on Thp-1 monocytic cells induced a Ca(2+) flux and the time-dependent activation of phosphotyrosine proteins ranging from 35 to 180 kDa. We identified the 140- and 85-kDa proteins as phospholipase C gamma (PLC-gamma) and the regulatory subunit of phosphatidylinositol 3-kinase (PI-3K), respectively. Using immunoprecipitation/Western immunoblotting however, we were unable to show any direct association between CD4 and PLC-gamma, PI-3K, or other known signaling proteins. To identify proteins capable of associating with the cytoplasmic tail of CD4, we fused it with gluthatione S-transferase and used the fusion protein in far Western and pull-down experiments. In both types of experiments, the fusion protein routinely associated with 45- and 55-kDa proteins. Mass spectrometry analysis of the tryptic peptides generated from these two proteins indicated novel sequences.