L. Spetch, T. L. Bowlin and A. Casola infection, but did not result in significant improvement of clinical disease administered 1 day after infection, when clinical disease and lung inflammation are already present (Castro et al., 2006). This finding suggests that early therapeutic intervention may be necessary to improve clinical outcome in both hMPV and RSV infections. In future studies, it would be important to assess other important parameters of clinical illness such as airway hyper-responsiveness, which has been reported in BALB/c mice infected with hMPV or with other paramyxoviruses such as RSV. Similarly, alternative methods of administration, for example via aerosolization, could be tested for efficacy. HMPV infection of BALB/c mice induces a significant lung inflammatory response, with recruitment of phagocytes and then mononuclear cells to the airways, concomitant with the induction of chemokines and cytokines. The role of the inflammatory response in hMPV-induced clinical illness has not yet been investigated. However, the recent finding of a significant reduction of body weight loss following glucocorticoid treatment (Hamelin et al., 2006) in a similar mouse model of hMPV infection suggests that modulating pulmonary inflammation would be beneficial in hMPV-induced disease. A recent in vitro study has shown that NMSO3 reduces RSV-induced chemokine production (Miller et al., 2004). Similarly, our results showed that NMSO3 treatment significantly reduced hMPV-induced chemokine/cytokine production, paralleled by a reduction in pulmonary inflammation. The only exception was secretion of KC, a neutrophil chemoattractant, which explains the relatively higher proportion of these phagocytic cells at day 4 p.i. in the NMSO3-treated group. Although this beneficial effect is probably due to the reduction in hMPV replication, it is possible that, in addition to its antiviral activity, NMSO3 may also possess general anti-inflammatory properties, as recently shown in vitro by inhibition of adhesion-dependent leukocyte activation (Shodai et al., 2003). We have recently shown that CD4+ T lymphocytes play an important role in modulating hMPV-induced clinical illness and pulmonary inflammation (Kolli et al., 2008). It is possible that NMSO3 treatment modulation of the innate response also modified the adaptive immune response, leading to a beneficial effect on disease that is not due only to the antiviral mechanism. Future studies should address whether NMSO3 modifies recruit- ment/maturation of dendritic cells and whether there are changes in the phenotype of T cells. In summary, NMSO3 treatment improved several aspects of hMPV-induced disease and should be considered for further evaluation in other animal models. 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