No abstract

Sporothrix schenckii is a human pathogen that causes sporotrichosis, an important cutaneous mycosis with a worldwide distribution. It produces dark-brown conidia, which infect the host. We found that S. schenckii synthesizes melanin via the 1,8-dihydroxynaphthalene pentaketide pathway. Melanin biosynthesis in the wild type was inhibited by tricyclazole, and colonies of the fungus were reddish brown instead of black on tricyclazole-amended medium. Two melanin-deficient mutant strains were analyzed in this study: an albino that produced normal-appearing melanin on scytalone-amended medium and a reddish brown mutant that accumulated and extruded melanin metabolites into its medium. Scytalone and flaviolin obtained from cultures of the reddish brown mutant were identified by thin-layer chromatography, high-performance liquid chromatography, and UV spectra. Transmission electron microscopy showed an electron-dense granular material believed to be melanin in wild-type conidial cell walls, and this was absent in conidial walls of the albino mutant unless the albino was grown on a scytalone-amended medium. Melanized cells of wild-type S. schenckii and the albino grown on scytalone-amended medium were less susceptible to killing by chemically generated oxygen- and nitrogen-derived radicals and by UV light than were conidia of the mutant strains. Melanized conidia of the wild type and the scytalone-treated albino were also more resistant to phagocytosis and killing by human monocytes and murine macrophages than were unmelanized conidia of the two mutants. These results demonstrate that melanin protects S. schenckii against certain oxidative antimicrobial compounds and against attack by macrophages.

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Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) cause a similar spectrum of respiratory infections in humans. Classified within the Paramyxoviridae family, Pneumovirinae subfamily, RSV and hMPV present a significant degree of divergence in genome constellation, organization, and protein sequences. RSV has been reported to be a poor inducer of alpha/beta interferons (IFN-␣/␤) and partially resistant to its antiviral activity. The nature of the innate immune response to hMPV is currently unknown. Herein, an experimental mouse model was used to investigate the interplay between RSV and hMPV infections and IFN-␣ in the airways. RSV-infected BALB/c mice treated intranasally with either poly-ICLC, a potent inducer of IFN-␣, or directly with recombinant IFN-␣ showed significantly reduced lung viral titers, inflammation, and clinical disease than untreated controls. However, RSV was significantly less sensitive to the antiviral activity of IFN-␣ than hMPV. Similarly, when the ability to directly induce IFN-␣ production was assessed, RSV was clearly a weaker inducer of IFN-␣ than hMPV, as shown by both kinetics and the absolute amount of IFN-␣ secreted into the bronchoalveolar lavage. To further investigate the putative inhibitory effect of these viruses on IFN-␣ production, mice were infected for 48 h prior to treatment with poly-ICLC or a specific Toll-like receptor 9 ligand, CpG oligodeoxynucleotides. Strikingly, both poly-ICLC-and CpG-mediated IFN-␣ production was abrogated by either RSV or MPV infection. These results suggest that a complex interplay between virus-specific and host-mediated responses regulates IFN-␣ in the lung during infection by members of the Pneumovirinae family.

Human metapneumovirus (hMPV), a member of the family Paramyxoviridae, is a leading cause of lower respiratory tract infections in children, the elderly, and immunocompromised patients. Virus-and host-specific mechanisms of pathogenesis and immune protection are not fully understood. By an intranasal inoculation model, we show that hMPV-infected BALB/c mice developed clinical disease, including airway obstruction and hyperresponsiveness (AHR), along with histopathologic evidence of lung inflammation and viral replication. hMPV infection protected mice against subsequent viral challenge, as demonstrated by undetectable viral titers, lack of body weight loss, and a significant reduction in the level of lung inflammation. No crossprotection with other paramyxoviruses, such as respiratory syncytial virus, was observed. T-lymphocyte depletion studies showed that CD4 ؉ and CD8 ؉ T cells cooperate synergistically in hMPV eradication during primary infection, but CD4؉ more than CD8 ؉ T cells also enhanced clinical disease and lung pathology. Concurrent depletion of CD4؉ and CD8 ؉ T cells completely blocked airway obstruction as well as AHR. Despite impaired generation of neutralizing anti-hMPV antibodies in the absence of CD4؉ T cells, mice had undetectable viral replication after hMPV challenge and were protected from clinical disease, suggesting that protection can be provided by an intact CD8 ؉ T-cell compartment. Whether these findings have implications for naturally acquired human infections remains to be determined.