Recombinant IFN-alpha (2b) increases the expression of apoptosis receptor CD95 and chemokine receptors CCR1 and CCR3 in monocytoid cells.

IFN-alpha-2b, known as potent immune modulator, can either inhibit or enhance immune cell activity within the tightly regulated microenvironment of inflammation, depending upon the concentration of the cytokine and the activation stage of the cell. Chemokine receptors, which not only mediate chemotaxis of immune cells to the site of inflammation but also affect cellular activation by transferring corresponding signals, represent yet another level of immune regulation. Here we demonstrate that IFN-alpha increases the expression of CCR1 and CCR3 in primary mononuclear phagocytes, as well as in the monocytoid cell line U937. Enhanced receptor mRNA expression correlated with functional readouts such as increased intracellular calcium mobilization and cell migration in response to ligands. Expression of CCR2b, CCR4, CCR5, and CXCR4 was unchanged or decreased after IFN-alpha treatment. These observations indicate a differentially regulated cellular signaling relationship of IFN-alpha pathways and chemokine receptor expression. We also provide evidence that, under these conditions, IFN-alpha treatment increased the expression of CD95 (Fas, Apo1), resulting in enhanced susceptibility to apoptosis. Taken together, these data add important information for the rational application of IFN-alpha (2b) in immune and cancer therapies.

Progressive and persistent downregulation of surface CXCR4 in CD4(+) T cells infected with human herpesvirus 7.

We have previously shown that infection of CD4(+) T lymphocytes with the T-lymphotropic human herpesvirus 7 (HHV-7) downregulates surface CD4, which represents the high-affinity receptor for HHV-7. In this study, we report that HHV-7 infection also causes a progressive loss of the surface CXC-chemokine receptor 4 (CXCR4) in CD4(+) T cells, accompanied by a reduced intracellular Ca2+ flux and chemotaxis in response to stromal cell-derived factor-1 (SDF-1), the specific CXCR4 ligand. Moreover, CXCR4 is downregulated from the surface of HHV-7-infected T cells independently of CD4. Because intracellular CXCR4 antigen and mRNA levels are unaffected in productively HHV-7-infected cells, the downregulation of CXCR4 apparently does not involve a transcritional block. Since CXCR4 functions in association with CD4 to permit entry of several human immunodeficiency virus (HIV) isolates, the potential of HHV-7 to persistently downregulate the surface expression of CXCR4 may provide novel strategies for limiting HIV infection.

Interferon-gamma increases expression of chemokine receptors CCR1, CCR3, and CCR5, but not CXCR4 in monocytoid U937 cells.

Chemokine receptors (CR), which can mediate migration of immune cells to the site of inflammation, also function as coreceptors for human immunodeficiency virus (HIV) entry into CD4+ T lymphocytes and antigen-presenting cells. We demonstrate here that interferon-gamma (IFN-gamma) increases the expression of chemokine receptors CCR1, CCR3, and CCR5 in monocytoid U937 cells as detected by cell surface molecule labeling and mRNA expression, as well as by intracellular calcium mobilization and cell migration in response to specific ligands. The increased expression of these chemokine receptors also results in an enhanced HIV-1 entry into cells. Our data provide evidence for a relationship of cellular pathways that are induced by IFN-gamma with those that regulate chemokine receptor expression.

Neither human immunodeficiency virus-1 (HIV-1) nor HIV-2 infects most-primitive human hematopoietic stem cells as assessed in long-term bone marrow cultures.

Attempts to clarify the pathophysiology of human immunodeficiency virus (HIV)-mediated bone marrow (BM) dysfunction have yielded inconsistent results regarding the susceptibility of BM progenitors to the viral infection. To specifically address this question, we exposed highly purified subpopulations of human BM progenitor cells to various HIV-1 and HIV-2 strains and assessed (pro)viral gene presence and expression in more-committed (CD34+CD38+) as well as most-primitive (CD34+CD38-) cells in long-term BM cultures. Quantitative analysis of long-term culture-initiating cells (LTCIC) failed to demonstrate adverse effects of exposing hematopoietic stem cells to HIV. Our results show that HIV-2, similar to HIV-1, does not infect hematopoietic stem cells in vitro with any significant frequency and infected cells are not present within LTCICs. Cytofluorometric analysis of CD34+ cells for surface molecules that facilitate HIV entry was consistent with the functional assay in that expression of virus receptors was predominantly on the more-committed subsets of BM progenitors. The failure to detect productive or latent HIV in the most-primitive human BM progenitor and stem cells has important implications for future therapeutic strategies, including those dealing with transduction of these cells with protective genes as a treatment modality for AIDS.