Merkel cell polyomavirus (MCV) is a recently discovered human virus closely related to African green monkey lymphotropic polyomavirus. MCV DNA is integrated in 80% of Merkel cell carcinomas (MCC), a neuroendocrine skin cancer linked to lymphoid malignancies such as chronic lymphocytic leukemia (CLL). To assess MCV infection and its association with human diseases, we developed a monoclonal antibody that specifically recognizes endogenous and transfected MCV large T (LT) antigen. We show expression of MCV LT protein localized to nuclei of tumor cells from MCC having PCR quantified MCV genome at an average of 5.2 (range 0.8-14.3) T antigen DNA copies per cell. Expression of this putative viral oncoprotein in tumor cells provides the mechanistic underpinning supporting the notion that MCV causes a subset of MCC. In contrast, although 2.2% of 325 hematolymphoid malignancies surveyed also showed evidence for MCV infection by DNA PCR, none were positive at high viral copy numbers, and none of 173 lymphoid malignancies examined on tissue microarrays expressed MCV LT protein in tumor cells. As with some of the other human polyomaviruses, lymphocytes may serve as a tissue reservoir for MCV infection, but hematolymphoid malignancies associated with MCC are unlikely to be caused by MCV. ' 2009 UICC
Exosomes are secreted cellular vesicles that can be internalized by dendritic cells (DCs), contributing to antigen-specific naive CD4 ؉ T-cell activation. Here, we demonstrate that human immunodeficiency virus type 1 (HIV-1) can exploit this exosome antigen-dissemination pathway intrinsic to mature DCs (mDCs) for mediating trans-infection of T lymphocytes. Capture of HIV-1, HIV-1 Gag-enhanced green fluorescent protein (eGFP) virallike particles (VLPs), and exosomes by DCs was up-regulated upon maturation, resulting in localization within a CD81 ؉ compartment. Uptake of VLPs or exosomes could be inhibited by a challenge with either particle, suggesting that the expression of common determinant(s) on VLP or exosome surface is necessary for internalization by mDCs. Capture by mDCs was insensitive to proteolysis but blocked when virus, VLPs, or exosomes were produced from cells treated with sphingolipid biosynthesis inhibitors that modulate the lipid composition of the budding particles. Finally, VLPs and exosomes captured by mDCs were transmitted to T lymphocytes in an envelope glycoproteinindependent manner, underscoring a new potential viral dissemination pathway. IntroductionDendritic cells (DCs) are specialized antigen-presenting cells that orchestrate innate and adaptive immune responses to invading pathogens. Immature DCs located in the peripheral mucosal tissues recognize and capture microbial pathogens, undergo maturation, and traffic to lymphoid tissues, where they induce adaptive immunity through antigen presentation to naive T cells. Although DCs are required to combat viral infections, viruses, including human immunodeficiency virus type 1 (HIV-1), have evolved strategies to evade their antiviral activity. HIV can gain access into DCs via a nonfusogenic endocytic mechanism, evade classical degradation pathways, and establish productive infection of DCinteracting T cells, a well-studied but poorly understood mechanism of HIV trans-infection of CD4 ϩ T cells.  The efficiency of DC-mediated HIV-1 transmission to T cells can be enhanced by maturing DCs in vitro, 2,4,5 although the mechanism underlying this process has not been well defined. 6 Previous studies have associated HIV trans-infection with the binding of the viral envelope glycoprotein (gp120) to C-type lectin receptors (CLR) such as DC-SIGN, trypsin-sensitive CLR, and CD4-independent receptors expressed on the DC surface. 3,7-11 However, we have recently identified an HIV gp120-independent mechanism of viral binding and endocytosis that is up-regulated upon DC maturation, 12 suggesting that HIV-1 might exploit a preexisting cellular pathway of antigen uptake and transmission. Interestingly, previous reports have shown that DCs can endocytose viral-like particles (VLPs) and induce immune responses. 13,14 Likewise, small secreted cellular organelles, termed exosomes, are also internalized by DCs and sorted into an endocytic compartment, stimulating antigenspecific naive CD4 ϩ T-cell activation in vivo. 15,16 On the basis of similarities i...
Dendritic cells (DCs) are specialized antigen-presenting cells. However, DCs exposed to human immunodeficiency virus type 1 (HIV-1) are also able to transmit a vigorous cytopathic infection to CD4؉ T cells, a process that has been frequently related to the ability of DC-SIGN to bind HIV-1 envelope glycoproteins. The maturation of DCs can increase the efficiency of HIV-1 transmission through trans infection. We aimed to comparatively study the effect of maturation in monocyte-derived DCs (MDDCs) and bloodderived myeloid DCs during the HIV-1 capture process. In vitro capture and transmission of envelopepseudotyped HIV-1 and its homologous replication-competent virus to susceptible target cells were assessed by p24 gag detection, luciferase activity, and both confocal and electron microscopy. Maturation of MDDCs or myeloid DCs enhanced the active capture of HIV-1 in a DC-SIGN-and viral envelope glycoprotein-independent manner, increasing the life span of trapped virus. Moreover, higher viral transmission of mature DCs to CD4 ؉ T cells was highly dependent on active viral capture, a process mediated through cholesterol-enriched domains. Mature DCs concentrated captured virus in a single large vesicle staining for CD81 and CD63 tetraspanins, while immature DCs lacked these structures, suggesting different intracellular trafficking processes. These observations help to explain the greater ability of mature DCs to transfer HIV-1 to T lymphocytes, a process that can potentially contribute to the viral dissemination at lymph nodes in vivo, where viral replication takes place and there is a continuous interaction between susceptible T cells and mature DCs.
Direct invasion from proliferating basaloid atypical keratinocytes limited to the epidermal basal layer (AK I), known as the differentiated pathway, was the most common form of progression to cutaneous iSCC in our series. On the other hand, stepwise progression from AK I to AK II and AK III (classic pathway) was seen to be operative in a substantial proportion of iSCC cases. All AK lesions, irrespective of intraepidermal neoplasia thickness, are therefore potentially invasive and tumour advance along adnexal structures might facilitate iSCC development from AK I lesions.
Mice lacking desmin produce muscle fibers with Z disks and normal sarcomeric organization. However, the muscles are mechanically fragile and degenerate upon repeated contractions. We report here a human patient with severe generalized myopathy and aberrant intrasarcoplasmic accumulation of desmin intermediate filaments. Muscle tissue from this patient lacks the wild-type desmin allele and has a desmin gene mutation encoding a 7-aa deletion within the coiled-coil segment of the protein. We show that recombinant desmin harboring this deletion cannot form proper desmin intermediate filament networks in cultured cells, nor is it able to assemble into 10-nm filaments in vitro. These findings provide direct evidence that a mutation in desmin can cause human myopathies.
Cell-to-cell virus transmission is one of the most efficient mechanisms of human immunodeficiency virus (HIV) spread, requires CD4 and coreceptor expression in target cells, and may also lead to syncytium formation and cell death. Here, we show that in addition to this classical coreceptor-mediated transmission, the contact between HIV-producing cells and primary CD4 T cells lacking the appropriate coreceptor induced the uptake of HIV particles by target cells in the absence of membrane fusion or productive HIV replication. HIV uptake by CD4 T cells required cellular contacts mediated by the binding of gp120 to CD4 and intact actin cytoskeleton. HIV antigens taken up by CD4 T cells were rapidly endocytosed to trypsin-resistant compartments inducing a partial disappearance of CD4 molecules from the cell surface. Once the cellular contact was stopped, captured HIV were released as infectious particles. Electron microscopy revealed that HIV particles attached to the surface of target cells and accumulated in large (0.5-1.0 m) intracellular vesicles containing 1-14 virions, without any evidence for massive clathrin-mediated HIV endocytosis. The capture of HIV particles into trypsin-resistant compartments required the availability of the gp120 binding site of CD4 but was independent of the intracytoplasmic tail of CD4. In conclusion, we describe a novel mechanism of HIV transmission, activated by the contact of infected and uninfected primary CD4 T cells, by which HIV could exploit CD4 T cells lacking the appropriate coreceptor as an itinerant virus reservoir.For many viruses, cell-to-cell virus transmission is the most efficient mechanism of viral spread because of the extremely low infectivity of free viral particles (1). In the case of human immunodeficiency virus (HIV), 1 free viral particles are infectious but show a short life span at 37°C (2) and lower infective capacity than cell-to-cell transmission (3). This latter phenomenon is favored by the polarization of viral production in the infected cell (4) and the viral receptors and coreceptors in the target cell leading to the formation of a functional (infectious) virological synapse (5, 6). Cell-to-cell virus transmission is probably involved in the spread of HIV among different populations of CD4 ϩ cells in vivo and seems to play an essential role in sexual or vertical transmission through epithelia (7,8).The process of membrane fusion induced by the envelope glycoprotein complex of HIV is independent of pH, and therefore endocytic internalization and endosomal acidification are not required to activate HIV entry into the cytoplasm (9 -12). Instead, viral entry involves direct fusion of viral and plasma cell membrane that allows for the delivery of the viral core into the cytoplasm of target cells (13). First, HIV envelope (gp120/gp41, Env) binds to CD4 and then to a chemokine receptor (CXCR4 for X4 strains and CCR5 for R5 strains), which is used by HIV particles to activate the gp41-mediated membrane fusion.A variety of cell types such as macrophages, endot...
Pityriasis lichenoides (PL) is a cutaneous disease of unknown origin, with an autoinvolutive course, that can occur in pediatric patients. Traditionally, acute and chronic variants have been described, but other special forms of presentation have been reported. We reviewed the clinical records and histopathologic specimens of all pediatric patients diagnosed with PL in our hospital from 1980 to 1995 to assess the clinicopathologic features of this disorder in our environment. Twenty-two of the 118 cases reviewed were pediatric patients less than 15 years old (12 males and 10 females, 18.6% of all patients). Their ages ranged from 3 to 15 years, with a mean of 9.3 years. Most of the patients (72%) had the chronic variant of the disease, while the remainder had an acute course. One patient suffered from acute ulceronecrotic PL. Systemic treatments prescribed were erythromycin in eight patients, PUVA in five patients, and methotrexate in one patient. Three patients had a prolonged course with more than two episodes. Acute and chronic PL are polar extremes, but individual cases cannot be classified only on the basis of histopathologic data, since coexistence of lesions in different stages of evolution can lead to sampling bias. Acute ulceronecrotic forms and the presence of a variable degree of cellular atypia in the infiltrate are liable to cause differential diagnostic problems with lymphomatoid papulosis (LP), which cannot be completely resolved on the basis of T-cell receptor clonal rearrangement detection.
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