A microRNA from infectious spleen and kidney necrosis virus modulates expression of the virus-mock basement membrane component VP08R.

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the genus Megalocytivirus, family Iridoviridae. Infection of ISKNV is characterized by a unique pathological phenomenon in that the infected cells are attached by lymphatic endothelial cells (LECs). ISKNV mediates the formation of a virus-mock basement membrane (VMBM) structure on the surface of infected cells to provide attaching sites for LECs. The viral protein VP08R is an important component of VMBM. In this study, a novel ISKNV-encoded microRNA, temporarily named ISKNV-miR-1, was identified. ISKNV-miR-1 is complementary to the VP08R-coding sequence and can modulate VP08R expression through reducing its mRNA level. This suggests that formation of VMBM may be under fine regulation by ISKNV.

Subcapsular sinus macrophages promote NK cell accumulation and activation in response to lymph-borne viral particles.

Natural killer (NK) cells become activated during viral infection in response to cytokines or to engagement of NK cell activating receptors. However, the identity of cells sensing viral particles and mediating NK cell activation has not been defined. Here, we show that local administration of a modified vaccinia virus Ankara vaccine in mice results in the accumulation of NK cells in the subcapsular area of the draining lymph node and their activation, a process that is strictly dependent on type I IFN signaling. NK cells located in the subcapsular area exhibited reduced motility and were found associated with CD169(+)-positive subcapsular sinus (SCS) macrophages and collagen fibers. Moreover, depletion of SCS macrophages using clodronate liposomes abolished NK cell accumulation and activation. Our results identify SCS macrophages as primary mediators of NK cell activation in response to lymph-borne viral particles suggesting that they act as early sensors of local infection or delivery of viral-based vaccines.

Depletion of macrophages in mice results in higher dengue virus titers and highlights the role of macrophages for virus control.

Monocytes and macrophages are target cells for dengue infection. Besides their potential role for virus replication, activated monocytes/macrophages produce cytokines that may be critical for dengue pathology. To study the in vivo role of monocytes and macrophages for virus replication, we depleted monocytes and macrophages in IFN-alphabetagammaR knockout mice with clodronate liposomes before dengue infection. Although less virus was first recovered in the draining LN in the absence of macrophages, monocyte/macrophage depletion eventually resulted in a ten-fold higher systemic viral titer. A massive infiltration of CD11b(+)CD11c(low)Ly6C(low) monocytes into infected organs was observed in parallel with increasing virus titers before viremia was controlled. Depletion of monocytes in the blood before or after local infection had no impact on virus titers, suggesting that monocytes are not required as "virus-shuttles". Our data provide evidence that systemic viremia is established independently of tissue macrophages present at the site of infection and blood monocytes. Instead, we demonstrate the importance of monocytes/macrophages for the control of dengue virus.

Bluetongue virus targets conventional dendritic cells in skin lymph.

Bluetongue virus (BTV) is the etiological agent of bluetongue, a hemorrhagic disease of ruminants (particularly sheep), which causes important economic losses around the world. BTV is transmitted primarily via the bites of infected midges, which inject the virus into the ruminant's skin during blood feeding. The virus initially replicates in the draining lymph node and then disseminates to secondary organs where it induces edema, hemorrhages, and necrosis. In this study, we show that ovine conventional dendritic cells (cDCs) are the primary targets of BTV that contribute to the primary dissemination of BTV from the skin to draining lymph nodes. Lymph cDCs support BTV RNA and protein synthesis, as well as the production of infectious virus belonging to several different BTV serotypes, regardless of their level of attenuation. Afferent lymph cell subsets, other than cDCs, showed only marginal levels of BTV protein expression. BTV infection provoked a massive recruitment of cDCs to the sheep skin and afferent lymph, providing cellular targets for infection. Although BTV productively infects cDCs, no negative impact on their physiology was detected. Indeed, BTV infection and protein expression in cDCs enhanced their survival rate. Several serotypes of BTV stimulated the surface expression of the CD80 and CD86 costimulatory molecules on cDCs as well as the mRNA synthesis of cytokines involved in inflammation and immunity, i.e., interleukin-12 (IL-12), IL-1beta, and IL-6. BTV-infected cDCs stimulated antigen-specific CD4 and CD8 proliferation as well as gamma interferon production. BTV initially targets cDCs while preserving their functional properties, reflecting the optimal adaptation of the virus to its host cells for its first spread.

Subcapsular sinus macrophages in lymph nodes clear lymph-borne viruses and present them to antiviral B cells.

Lymph nodes prevent the systemic dissemination of pathogens such as viruses that infect peripheral tissues after penetrating the body's surface barriers. They are also the staging ground of adaptive immune responses to pathogen-derived antigens. It is unclear how virus particles are cleared from afferent lymph and presented to cognate B cells to induce antibody responses. Here we identify a population of CD11b+CD169+MHCII+ macrophages on the floor of the subcapsular sinus (SCS) and in the medulla of lymph nodes that capture viral particles within minutes after subcutaneous injection. Macrophages in the SCS translocated surface-bound viral particles across the SCS floor and presented them to migrating B cells in the underlying follicles. Selective depletion of these macrophages compromised local viral retention, exacerbated viraemia of the host, and impaired local B-cell activation. These findings indicate that CD169+ macrophages have a dual physiological function. They act as innate 'flypaper' by preventing the systemic spread of lymph-borne pathogens and as critical gatekeepers at the lymph-tissue interface that facilitate the recognition of particulate antigens by B cells and initiate humoral immune responses.

Active simian immunodeficiency virus (strain smmPGm) infection in macaque central nervous system correlates with neurologic disease.

Simian immunodeficiency virus strain smmPGm can induce neuropathology in macaques and is a model for the development of human HIV-related brain injury. For quantitative studies of proviral presence and expression in the central nervous system (CNS), we inoculated 8 macaques intravenously with the virus. Three animals were necropsied 2 to 4 weeks after development of infection, and we obtained lymphoid tissue biopsies from 5 animals before 5 weeks after infection. Peak plasma viral loads averaged 10 viral RNA Eq/mL at week 2, whereas cerebrospinal fluid viral loads peaked at 10 viral RNA Eq/mL. The proviral DNA loads and viral gag mRNA expression in tissues were quantified by real-time polymerase chain reaction. Two animals developed neurologic disease characterized by meningoencephalitis and meningitis. Proviral DNA levels in CNS tissues of these animals at necropsy revealed 10 and 10 copies/microg of DNA, respectively, whereas viral RNA expression in the CNS reached 100 to 1000 times higher levels than those seen in early necropsies. In sharp contrast, in 2 animals necropsied at later times without CNS disease, virus mRNA expression was not detected in any CNS tissue. Our results are consistent with the hypothesis that active virus expression in the CNS is strongly correlated with neurologic disease and that the event occurs at variable periods after infection.

Infection of dendritic cells by the Maedi-Visna lentivirus.

The early stages of lentivirus infection of dendritic cells have been studied in an in vivo model. Maedi-visna virus (MVV) is a natural pathogen of sheep with a tropism for macrophages, but the infection of dendritic cells has not been proven, largely because of the difficulties of definitively distinguishing the two cell types. Afferent lymphatic dendritic cells from sheep have been phenotypically characterized and separated from macrophages. Dendritic cells purified from experimentally infected sheep have been demonstrated not only to carry infectious MVV but also to be hosts of the virus themselves. The results of the in vivo infection experiments are supported by infections of purified afferent lymph dendritic cells in vitro, in which late reverse transcriptase products are demonstrated by PCR. The significance of the infection of afferent lymph dendritic cells is discussed in relation to the initial spread of lentivirus infection and the requirement for CD4 T cells.

Accidental injuries by HIV-contaminated instruments in health provider or research environments: can seroconversion be prevented?

The rate of seroconversion from percutaneous needlestick exposure to HIV infection is approximately 0.3 per cent. To investigate the possibility of local confinement of HIV, 100 to 200 nm Tc-99m sulfur colloid particles were injected in the canine model subcutaneously at the knee level and collected proximally at the groin from the cannulated femoral vein and lymphatic channel. Tourniquet compression (250 mm Hg) was used as an intervention to possibly restrict particle spread. It was found that particles arrived in the blood at 2.81 +/- 0.54 minutes, with later arrival in the lymph at 6.0 +/- 1.47 minutes. Tourniquet application delayed the appearance of the particulate matter in the blood up to 7.11 +/- 1.5 minutes and in lymph up to 40.0 +/- 5.10 minutes. The concentration of radioactivity in the lymph was higher than in the venous blood. The distribution of the particles reflected by flux was comparable in both pathways. The accumulation curves did not reach plateaus during 45 minutes in lymph and 15 minutes in blood. Radioactive scanning revealed that about 90 per cent of the injected particles remained locally with gradual release for at least 45 minutes. Our results suggest that HIV, introduced by needlestick injury, can be contained for possible viricidal treatment if the response includes rapid immobilization and tourniquet of the area.

[AIDS: new developments. VI. HIV reservoirs during intensive antiretroviral treatment]. / AIDS: nieuwe ontwikkelingen. VI. HIV-reservoirs tijdens krachtige antiretrovirale behandeling.

Treatment of human immunodeficiency virus (HIV) infected persons with potent antiretroviral combination therapy results in a strong decline of the viral load in the blood. Whether this effect is reached in all tissues and different infected cell types is an important question. There are several potential virus reservoirs. Lymphoid tissue constitutes the largest virus compartment. With potent, often protease inhibitor containing combinations the HIV-RNA decline in lymphoid tissue runs parallel to that in the blood. The central nervous tissue is a potentially important reservoir, because of the limited penetration of several antiretrovirals, especially protease inhibitors. A few short studies with different combinations showed a decline of the amount of virus in the cerebrospinal fluid. The risk of local resistance developing is not known. There are only few studies of the effects of potent anti-HIV therapy on semen but prostate and testis tissue do not appear inaccessible to treatment. The reservoir of latently infected cells that cannot be reached by the immune system or by the viral replication inhibiting therapy, can possibly be reached with immune stimulating agents. This will cause HIV replication and cell death, while the anti-HIV therapy will prevent further replication of the produced virions. This approach is still experimental, however.

EBV persistence in memory B cells in vivo.

Epstein-Barr virus establishes latency in vitro by activating human B cells to become proliferating blasts, but in vivo it is benign. In the peripheral blood, the virus resides latently in resting B cells that we now show are restricted to the sIgD memory subset. However, in tonsils the virus shows no such restriction. We propose that EBV indiscriminately infects B cells in mucosal lymphoid tissue and that these cells differentiate to become resting memory B cells that then enter the circulation. Activation to the blastoid stage of latency is an essential intermediate step in this process. Thus, EBV may persist by exploiting the mechanisms that produce and maintain long-term B cell memory.