It is presumed that resolution of hepatitis C, as evidenced by normalization of liver function tests and disappearance of hepatitis C virus (HCV) RNA from serum, as determined by conventional laboratory assays, reflects virus eradication. In this study, we examined the expression of the HCV genome in the sera, peripheral blood mononuclear cells (PBMC), and, on some occasions, monocyte-derived dendritic cells (DC) long after resolution of hepatitis C by using a highly sensitive reverse transcription ( Hepatitis C virus (HCV) is a small positive-strand RNA virus of approximately 9,400 nucleotides that chronically infects an estimated 170 to 350 million people worldwide. Of those acutely afflicted, only 15% recover, while the remaining 85% succumb to chronic hepatitis (4). Furthermore, up to onefifth of the individuals with chronic hepatitis C progress to cirrhosis, and these patients are at a greater risk of developing hepatocellular carcinoma (9).It is generally accepted that HCV replicates by making a cRNA strand known as the negative or replicative strand. Although the liver is the main site of virus replication, there is an increasing body of evidence for virus propagation in extrahepatic locations, including cells of the lymphatic and the central nervous systems (17,28). In regard to infection of lymphoid cells, HCV positive and negative strands were detected in the peripheral blood mononuclear cells (PBMC) and the bone marrow from chronically infected patients (26,29,37). It was also shown that HCV can propagate in lymphoid cell cultures and that the virus derived is infectious (33, 34). The notion of natural HCV tropism for lymphoid cells is supported by a significant overrepresentation of certain lymphoproliferative disorders in the HCV-infected population. For instance, type II mixed cryoglobulinemia occurs 11 times more frequently in patients with HCV than in those without (6). Also, nonHodgkin lymphoma appears to be, albeit less strongly, associated with HCV infection (24).The current RT-PCR-based assay approved for clinical diagnostics, i.e., the Amplicor HCV v2.0 assay (Roche Molecular Diagnostics, Pleasanton, Calif.), detects HCV RNA with a sensitivity of 1,000 virus genomic equivalents (vge) per ml (or 500 IU/ml). Other assays can identify HCV RNA at 52 vge/ml (or 10 IU/ml) (i.e., the Versant HCV RNA qualitative assay; Bayer Corp., Tarrytown, N.J.). This implies that small quantities of HCV occurring either in serum or within cells may escape detection. Therefore, considering the natural history of HCV infection, there exists a possibility that the virus may not be completely eradicated at the time of clinical and serological resolution of hepatitis. This situation may occur following spontaneous recovery or antiviral therapy.Lymphotropism is a characteristic of many DNA and RNA viruses capable of inducing persistent infection (8,27). A number of studies, including those with highly hepatotropic hepatitis B virus (19, 30) and woodchuck hepatitis virus (3,21,22), have demonstrated that pathogenic vir...

No abstract

HIV up-regulates cell-surface expression of specific ligands for the activating NKG2D receptor, including ULBP-1, -2, and -3, but not MICA or MICB, in infected cells both in vitro and in vivo. However, the viral factor(s) involved in NKG2D ligand expression still remains undefined. HIV-1 Vpr activates the DNA damage/stress-sensing ATR kinase and promotes G(2) cell-cycle arrest, conditions known to up-regulate NKG2D ligands. We report here that HIV-1 selectively induces cell-surface expression of ULBP-2 in primary CD4(+) T lymphocytes by a process that is Vpr dependent. Importantly, Vpr enhanced the susceptibility of HIV-1-infected cells to NK cell-mediated killing. Strikingly, Vpr alone was sufficient to up-regulate expression of all NKG2D ligands and thus promoted efficient NKG2D-dependent NK cell-mediated killing. Delivery of virion-associated Vpr via defective HIV-1 particles induced analogous biologic effects in noninfected target cells, suggesting that Vpr may act similarly beyond infected cells. All these activities relied on Vpr ability to activate the ATR-mediated DNA damage/stress checkpoint. Overall, these results indicate that Vpr is a key determinant responsible for HIV-1-induced up-regulation of NKG2D ligands and further suggest an immunomodulatory role for Vpr that may not only contribute to HIV-1-induced CD4(+) T-lymphocyte depletion but may also take part in HIV-1-induced NK-cell dysfunction.

Hepatitis C virus (HCV) is one of the main causes of chronic liver disease. Although infection of hepatocytes is mainly responsible for manifestations of hepatitis C, the virus also invades the immune system by a yet-to-be-identified mechanism. Using human T cell lines and primary T lymphocytes as targets and patient-derived HCV as inocula, we aimed to identify how HCV gains entry into these cells. HCV replication was determined by detection of the HCV RNA replicative (negative) strand and viral proteins, while specific antibodies, knocking down gene expression and making otherwise-resistant cells prone to HCV, were employed to identify a receptor molecule determining T lymphocyte permissiveness to HCV infection. The results revealed that T cell susceptibility to HCV requires CD5, a lymphocyte-specific glycoprotein belonging to the scavenger receptor cysteine-rich family. Blocking of T cell CD5 with antibody or silencing with specific short hairpin RNA (shRNA) decreased cell susceptibility to HCV, while increasing CD5 expression by mitogen stimulation had the opposite effect. Moreover, transfection of naturally CD5-deficient HEK-293 fibroblasts with CD5 facilitated infection of these otherwise HCV-resistant cells. In contrast to T cells, hepatocytes do not express CD5. The data revealed that CD5 is a molecule important for HCV entry into human T lymphocytes. This finding provides direct insight into the mechanism of HCV lymphotropism and defines a target for potential interventions against HCV propagating in this extrahepatic compartment.

BackgroundHIV proteins Nef and Vpu down-modulate various host factors to evade immune defenses. Indeed, the CD4 receptor is down-regulated by Nef and Vpu, whereas virion-tethering BST2 is depleted by Vpu. Antibody-dependent cell-mediated cytotoxicity (ADCC) is increasingly recognized as a potentially powerful anti-HIV response. Given that epitopes which are specific for ADCC-competent anti-HIV antibodies are transitionally exposed upon CD4-mediated HIV entry, we investigated whether by depleting CD4 and BST2, HIV could negatively affect ADCC function.ResultsUsing anti-envelope (Env) Abs A32 and 2G12 to trigger ADCC activity, we find that interactions between CD4 and Env within infected cells expose ADCC-targeted epitopes on cell-surface Env molecules, marking infected T cells for lysis by immune cells. We also provide evidence to show that by cross-linking nascent virions at the plasma membrane, hence increasing cell-surface Env density, BST2 further enhances the efficiency of this antiviral process. The heightened susceptibility of T cells infected with a virus lacking Nef and Vpu to ADCC was recapitulated when plasmas from HIV-infected patients were used as an alternative source of Abs.ConclusionsOur data unveil a mechanism by which HIV Nef and Vpu function synergistically to protect infected cells from ADCC and promote viral persistence. These findings also renew the potential practical relevance of ADCC function in vivo.

Hepatitis C virus (HCV) can persist in the liver, lymphoid cells, and serum of individuals with apparently complete spontaneous or therapy-induced resolution of hepatitis C and can replicate in vivo and in vitro in human T cells. The current study was aimed at assessing the infectivity of HCV persisting at very low levels using the previously established HCV infection system in human T cells. Naive lymphoid cells were exposed to plasma and/or supernatants from cultured peripheral blood mononuclear cells from nine individuals with apparent sustained virological response after completion of antiviral therapy. ting infection in chimpanzees. 1 Recently, the introduction of nucleic acid amplification assays detecting HCV genomes with enhanced sensitivity, which has reached in our laboratory Ͻ10 virus genomes or virus genome equivalents (vge)/mL or Ͻ2 IU/mL, has revealed that HCV can persist at low levels in individuals with apparently com-

While exploring previous findings that ex vivo treatment of lymphoid cells from Hepatitis C virus (HCV)-infected individuals with T cell-stimulating mitogens augments detection of the residing virus, an in vitro HCV replication system was established, in which mitogen-induced T cell-enriched cultures served as HCV targets and the derived T cells multiplied virus during repeated serial passage. HCV replication was ascertained by detecting HCV RNA positive and negative strands, HCV NS5a and E2 proteins, release of HCV virions and nucleocapsids (confirmed by immunoelectron microscopy) and de novo infection of mitogen-induced T cells prepared from healthy donors. Further, affinity-purified normal human T lymphocytes were also susceptible to HCV infection in vitro and HCV replication was detected in pure T cells isolated from a patient with chronic hepatitis C. These results document that T cells can support propagation of HCV both in vivo and in vitro. The infection system established offers a valuable tool for in vitro studies on the entire cycle of HCV replication, virus cytopathogenicity and evaluation of antiviral agents against wild-type HCV in the natural host-cell milieu.

SARS-CoV-2, the etiological agent of COVID-19, has so far resulted in >6.1 million deaths worldwide. The spike protein (S) of the virus directs infection of the lungs and other tissues by binding the angiotensin-converting enzyme 2 (ACE2) receptor.