The type I interferon-inducible factor tetherin retains virus particles on the surfaces of cells infected with vpu-deficient human immunodeficiency virus type 1 (HIV-1). While this mechanism inhibits cell-free viral spread, the immunological implications of tethered virus have not been investigated. We found that surface tetherin expression increased the antibody opsonization of vpudeficient HIV-infected cells. The absence of Vpu also stimulated NK cell-activating Fc␥RIIIa signaling and enhanced NK cell degranulation and NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC). The deletion of vpu in HIV-1-infected primary CD4؉ T cells enhanced the levels of antibody binding and Fc receptor signaling mediated by HIV-positive-patient-derived antibodies. The magnitudes of antibody binding and Fc signaling were both highly correlated to the levels of tetherin on the surfaces of infected primary CD4 T cells. The affinity of antibody binding to Fc␥RIIIa was also found to be critical in mediating efficient Fc activation. These studies implicate Vpu antagonism of tetherin as an ADCC evasion mechanism that prevents antibody-mediated clearance of virally infected cells. IMPORTANCEThe ability of the HIV-1 accessory factor to antagonize tetherin has been considered to primarily function by limiting the spread of virus by preventing the release of cell-free virus. This study supports the hypothesis that a major function of Vpu is to decrease the recognition of infected cells by anti-HIV antibodies at the cell surface, thereby reducing recognition by antibody-dependent clearance by natural killer cells.

Our objective was to examine the association between myocardial infarction (MI) and two DNA-polymorphisms at the proinflammatory chemokine receptors CCR2 (I64V) and CCR5 (32 bp deletion, (Delta)ccr5), defining if these polymorphisms influence the age for the onset of MI. A total of 214 patients with an age at the first MI episode <55 years, 96 patients that suffered the first MI episode when older than 60 years, and 360 population controls were polymerase chain reaction genotyped for the CCR2-V64I and CCR5-Delta32/wt polymorphisms. Patients and controls were male from the same Caucasian population (Asturias, northern Spain). The frequency of the Deltaccr5 allele was significantly higher in controls compared to patients <55 years (P = 0.004), or in patients >60 years compared to patients <55 years (P = 0.002). Taking the patients >60 years as the reference group, non-carriers of the (Delta)ccr5-allele would have a three-fold higher risk of suffering an episode of MI at <55 years of age (OR = 3.06; 95% CI = 1.46-6.42). Gene and genotype frequencies for the CCR2 polymorphism did not differ between patients <55 years and controls or patients >60 years. Our data suggest that the variation at the CCR5 gene could modulate the age at the onset of MI. Patients carrying the (Delta)ccr5-allele would be protected against an early episode of MI. CCR5 and the CCR5-ligands are expressed by cells in the arteriosclerotic plaque. Thus, the protective role of (Delta)ccr5 could be a consequence of an attenuated inflammatory response, that would determine a slower progression of the arteriosclerotic lesion among (Delta)ccr5-carriers. Our work suggests that the pharmacological blockade of CCR5 could be a valuable therapy in the treatment of MI.

Andes hantavirus (ANDV) is an etiologic agent of hantavirus cardiopulmonary syndrome (HCPS), a severe disease characterized by fever, headache, and gastrointestinal symptoms that may progress to hypotension, pulmonary failure, and cardiac shock that results in a 25 to 40% case-fatality rate. Currently, there is no specific treatment or vaccine; however, several studies have shown that the generation of neutralizing antibody (Ab) responses strongly correlates with survival from HCPS in humans. In this study, we screened 27 ANDV convalescent HCPS patient sera for their capacity to bind and neutralize ANDV in vitro. One patient who showed high neutralizing titer was selected to isolate ANDV–glycoprotein (GP) Abs. ANDV-GP–specific memory B cells were single cell sorted, and recombinant immunoglobulin G antibodies were cloned and produced. Two monoclonal Abs (mAbs), JL16 and MIB22, potently recognized ANDV-GPs and neutralized ANDV. We examined the post-exposure efficacy of these two mAbs as a monotherapy or in combination therapy in a Syrian hamster model of ANDV-induced HCPS, and both mAbs protected 100% of animals from a lethal challenge dose. These data suggest that monotherapy with mAb JL16 or MIB22, or a cocktail of both, could be an effective post-exposure treatment for patients infected with ANDV-induced HCPS.

The chemokine stromal cell-derived factor (SDF)-1 and its receptor, CXCR4, play important roles in human immunodeficiency virus type 1 (HIV-1) pathophysiology, leukocyte trafficking, inflammation, hematopoiesis, embryogenesis, angiogenesis, and cancer metastasis. The effects of cytokines on the regulation of CXCR4 function were investigated in human primary monocytes-macrophages. The expression of functional CXCR4 on the cell surface was demonstrated by the detection of ligandinduced Ca 2؉ mobilization, chemotaxis, and ligand-induced receptor endocytosis. Surface CXCR4 expression was down-regulated by cytokines interleukin-4 (IL-4), IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF) and up-regulated by IL-10 and transforming growth factor-␤1. Down-regulation was mediated post-translationally, in the absence of protein degradation, through an endocytotic mechanism. In contrast to SDF-1␣-induced CXCR4 endocytosis, cytokine-induced endocytosis of this receptor was independent of actin filament polymerization. GM-CSF increased the expression of G protein-coupled receptor kinase 3 (GRK3), ␤-arrestin-1, Pyk2, and focal adhesion kinase (FAK). Cytokine treatment also increased the total and tyrosine-specific phosphorylation of CXCR4 as well as the phosphorylation of FAK on tyrosine 397. It also induced the formation of GRK3⅐CXCR4 or FAK⅐CXCR4 complexes. Infection of macrophages by primary R5X4 and X4 isolates of HIV-1 was inhibited by IL-4, IL-13, and GM-CSF, an effect that was associated with down-regulation of surface CXCR4 expression. These data indicate that ligand-dependent and ligand-independent endocytoses of CXCR4 are mediated by different mechanisms. Cytokine-induced endocytosis of chemokine receptors may be of therapeutic value in HIV-1 infection, inflammation, tumor metastasis, and defective hematopoiesis.Macrophages and T lymphocytes are the major targets of HIV-1 1 infection and constitute the productive viral reservoirs (1, 2). Three types of HIV-1 isolates that infect macrophages have been identified and differ according to the chemokine receptor targeted for use as a viral coreceptor: (i) R5 viruses infect macrophages and primary CD4 ϩ T cells through CCR5 and constitute the principal virus type transmitted in vivo, as indicated by the resistance to HIV-1 infection of individuals who lack functional CCR5(3-5). (ii) Primary X4 viruses that have not been subjected to extensive passage in vitro use CXCR4 as a coreceptor and infect primary CD4 ϩ T cells, T cell lines, and macrophages (6). These viruses emerge later in infection than do R5 viruses and are associated with disease progression. Laboratory-adapted X4 viruses lose the ability to infect macrophages but still replicate in primary CD4 ϩ T cells and T cell lines. (iii) R5X4 viruses infect macrophages through either CCR5 or CXCR4 (7, 8) and may represent an important intermediate viral phenotype during the transition from R5 to X4 virus types (9) during the course of infection.Host factors are important contributors to the pathogenesi...

An elaborate network of cell-cell interactions in the immune system is essential for vertebrates to mount adaptive immune responses against invading pathogens. For lymphotropic viruses such as the human immunodeficiency virus type 1 (HIV-1), these immune cell interactions can also promote the spread of the virus within the host. The main target of HIV-1 infection is the CD4(+) helper T lymphocyte, a cell type that is responsible for coordinating immune responses and modulating effector responses to foreign antigens. As part of their normal immune surveillance duties, these cells migrate actively within lymphoid tissues and can travel from inductive sites to effector sites in search of their cognate antigen. For CD4(+) T cells, there is an ongoing search for a unique peptide antigen presented in the context of class II MHC that can activate a proliferative or tolerogenic response. This iterative and continual probing and interrogation of other cells determine the outcome of immune responses. Recent studies in vitro have revealed that the viral infection program induces cell-cell interactions called virological synapses between infected and uninfected CD4(+) T cells. These long-lived, virally induced adhesive contacts greatly enhance the rate of productive infection and may be central to the spread of the virus in vivo. Here, we review aspects of this efficient mode of cell-to-cell infection and the implications for our understanding of HIV-1 pathogenesis.