Human metapneumovirus (hMPV) is associated with respiratory tract infections among children and adults. Because hMPV induces significant morbidity and mortality in the elderly, a model of hMPV infection in aged BALB/c mice was established. Young (8 weeks old) and aged (18 months old) mice were intranasally inoculated with hMPV. The infected mice showed respiratory dysfunction, as measured by plethysmography, a marked loss in weight (up to 24%), and severe histopathological abnormalities including bronchiolitis obliterans organizing pneumonia. However, clinical severity was far higher in the aged mice, and none of the young infected mice died. Although virus replication in the lung was greater in the older mice, clearance of virus was not delayed compared to young mice. Production of virus-specific antibody as well as neutralizing antibody was lower. Gamma interferon and monocyte chemotactic protein-1 levels in bronchoalveolar lavage fluid were significantly lower in older mice, whereas interleukin-6 and interleukin-4 levels were significantly higher. We observed by flow cytometry a significant increase in the CD4(+) T lymphocytes (P<0.05) of the aged mice and no difference in CD8(+) T-cell recruitment to the respiratory tract between the two groups. The present study investigated the effects of aging on the immunopathogenesis of hMPV infection and suggests that CD4(+) T lymphocytes, the cytokine response, or a defect in humoral response may be associated with the increased disease severity observed in the aged mice.

Human metapneumovirus, with two known genotypes named A and B, is associated with mild respiratory symptoms to severe LRTI in children, high-risk adults and the elderly. Rapid and reliable methods of hMPV detection in clinical samples are essential to implement appropriate care, to better understand the pathology of hMPV and to determine its epidemiology. Respiratory samples from 1,386 patients collected during 2 consecutive years were screened for hMPV using indirect immunofluorescence (IFA) assay with a monoclonal antibody. Forty-three patients tested positive for hMPV by the IFA method. In parallel, the samples were examined with RT-PCR on the F gene. Of these, 41 specimens were RT-PCR positive. The remaining two IF positives were cultured and the cultures were subsequently RT-PCR positive. IFA showed therefore a sensitivity of 100%. No false positive signals were obtained with the influenza virus, respiratory syncytial virus or parainfluenza. When tested by RT-PCR, all IFA-negative samples (n = 204)were found negative. Therefore the specificity of IFA was 100%, IC95 [98-100%], with a negative predictive value of 100%. Based upon phylogenetic analysis of the fusion gene, both subgroups of hMPV were efficiently detected by IFA, and the viral aetiology could be given in 2 hr. These results demonstrate the potential usefulness of immunofluorescence with our monoclonal antibody for the rapid detection of hMPV in clinical specimens in the management of therapy and the control of nosocomial diffusion.

ABSTRACTRotavirus (RV) is the main etiological agent of severe gastroenteritis in infants, and vaccination seems the most effective way to control the disease. Recombinant rotavirus-like particles composed of the viral protein 6 (VP6) and VP2 (2/6-VLPs) have been reported to induce protective immunity in mice when administered by the intranasal (i.n.) route. In this study, we show that administration of 2/6-VLPs by the intrarectal (i.r.) route together with either cholera toxin (CT) or a CpG-containing oligodeoxynucleotide as the adjuvant protects adult mice against RV infection. Moreover, when CT is used, RV shedding in animals immunized by the i.r. route is even reduced in comparison with that in animals immunized by the i.n. route. Humoral and cellular immune responses induced by these immunization protocols were analyzed. We found that although i.r. immunization with 2/6-VLPs induces lower RV-specific immunoglobulin G (IgG) and IgA levels in serum, intestinal anti-RV IgA production is higher in mice immunized by the i.r. route. Cellular immune response has been evaluated by measuring cytokine production by spleen and Peyer's patch cells (PPs) after ex vivo restimulation with RV. Mice immunized by the i.n. and i.r. routes display higher gamma interferon production in spleen and PPs, respectively. In conclusion, we demonstrate that i.r. immunization with 2/6-VLPs protects against RV infection in mice and is more efficient than i.n. immunization in inducing an anti-RV immune response in intestinal mucosa.

Human metapneumovirus (hMPV), a recently identified virus, causes upper and lower respiratory tract diseases. In this study, we show that BALB/c mice inoculated with hMPV exhibited significant morbidity on 1–2 days post-infection, when airway obstruction was found. Increased airway hyper-responsiveness to metacholine was found on day 4 concurrent with lung viral replication. Both IgG1 and IgG2a hMPV-specific antibodies were found in sera, while interferon-gamma (IFN-γ) and interleukin-4 (IL-4) were found in bronchoalveolar lavage. Lung histology showed parenchymal pneumonia and increased lymphocytic infiltration. We present here an animal model that may be helpful in studying hMPV pathogenesis and evaluating the effects of vaccines.