Citations

ABSTRACT This study focused on the in vitro infection of mouse and human neuroblastoma cells and the in vivo infection of the murine central nervous system with a recombinant measles virus. An undifferentiated mouse neuroblastoma cell line (TMN) was infected with the vaccine strain of measles virus (MVeGFP), which expresses enhanced green fluorescent protein (EGFP). MVeGFP infected the cells, and cell-to-cell spread was studied by virtue of the resulting EGFP autofluorescence, using real-time confocal microscopy. Cells were differentiated to a neuronal phenotype, and extended processes, which interconnected the cells, were observed. It was also possible to infect the differentiated neuroblastoma cells (dTMN) with MVeGFP. Single autofluorescent EGFP-positive cells were selected at the earliest possible point in the infection, and the spread of EGFP autofluorescence was monitored. In this instance the virus used the interconnecting processes to spread from cell to cell. Human neuroblastoma cells (SH-SY-5Y) were also infected with MVeGFP. The virus infected these cells, and existing processes were used to initiate new foci of infection at distinct regions of the monolayer. Transgenic animals expressing CD46, a measles virus receptor, and lacking interferon type 1 receptor gene were infected intracerebrally with MVeGFP. A productive infection ensued, and the mice exhibited clinical signs of infection, such as ataxia and an awkward gait, identical to those previously observed for the parental virus (Edtag). Mice were sacrificed, and brain sections were examined for EGFP autofluorescence by confocal scanning laser microscopy over a period of 6 h. EGFP was detected in discrete focal regions of the brain and in processes, which extended deep into the parenchyma. Collectively, these results indicate (i) that MVeGFP can be used to monitor virus replication sensitively, in real time, in animal tissues, (ii) that infection of ependymal cells and neuroblasts provides a route by which measles virus can enter the central nervous system in mouse models of encephalitis, and (iii) that upon infection, the virus spreads transneuronally.

ABSTRACTMurine Lyme borreliosis, caused by infection with the spirocheteBorrelia burgdorferi, results in acute arthritis and carditis that regress as a result ofB. burgdorferi-specific immune responses.B. burgdorferi-specific antibodies can attenuate arthritis in mice deficient in both B cells and T cells but have no effect on carditis. Because macrophages comprise the principal immune cell in carditis, T-cell responses that augment cell-mediated immunity may be important for carditis regression. To investigate this hypothesis, we examined the course of Lyme carditis in mice selectively deficient in B cells or αβ T cells. Our results show that carditis regresses in B-cell-deficient B10.Akmice but not in αβ T-cell-deficient mice, independently of the mouse strain background. Despite prominent macrophage infiltrates, hearts fromB. burgdorferi-infected αβ T-cell-deficient mice had less mRNA for tumor necrosis factor alpha as measured by reverse transcription-PCR compared to infected control mice. Anti-inflammatory cytokine mRNA levels were equivalent. Adoptive transfer of gamma interferon-secreting CD4+T cells into infected αβ T-cell-deficient mice promoted carditis resolution. These results show that αβ T cells can promote resolution of murine Lyme carditis and are the first demonstration of a beneficial role for CD4+T helper 1 cells in this disease.

ABSTRACT Cell entry of retroviruses is initiated by the recognition of cellular receptors and the subsequent membrane fusion between viral and cellular membranes. These two steps are mediated by the surface (SU) and transmembrane (TM) subunits of the retroviral envelope glycoprotein (Env), respectively. Determinants regulating membrane fusion have been described throughout SU and TM, but the processes coupling receptor recognition to fusion are still elusive. Here we establish that a critical interaction is formed between the receptor-binding domain (RBD) and the major disulfide loop of the carboxy-terminal domain (C domain) of the murine leukemia virus SU. Receptor binding causes an alteration of this interaction and, in turn, promotes further events of Env fusion activation. We characterize mutations which, by lowering this interaction and reducing the compatibility between the RBD and C domains of Env glycoprotein chimeras, affect both Env fusogenicity and sensitivity to receptor interference. Additionally, we demonstrate that suboptimal interactions in such mutant Env proteins can be compensated in trans by soluble RBDs in a manner that depends on their compatibility with the C domain. Our results therefore indicate that RBD/C domain interactions may occur in cis , via the proper RBD of the viral Env itself, or in trans , via a distinct RBD expressed by virion-free Env glycoproteins expressed endogenously by the infected cells or provided by neighboring Env trimers.

To test the hypothesis that actin dysfunction leads to heart failure, patients with hereditary idiopathic dilated cardiomyopathy (IDC) were examined for mutations in the cardiac actin gene ( ACTC ). Missense mutations in ACTC that cosegregate with IDC were identified in two unrelated families. Both mutations affect universally conserved amino acids in domains of actin that attach to Z bands and intercalated discs. Coupled with previous data showing that dystrophin mutations also cause dilated cardiomyopathy, these results raise the possibility that defective transmission of force in cardiac myocytes is a mechanism underlying heart failure.