As of this writing, we are still without safe and effective therapeutic strategies for acute respiratory virus infections. Despite considerable efforts over the almost 50 years since its first description, supportive therapy alone remains the standard of care for the treatment of severe cases of respiratory syncytial virus (RSV), a disease with significant morbidity and mortality, particularly among infants born prematurely, and for which there is currently no vaccine. Even when a vaccine is available for a respiratory pathogen, such as for epidemic influenza virus, similar problems of disease prevention and management exist despite seasonal reformulation of vaccine preparations. While progress has been made toward the development of agents with antiviral activity in vitro, the clinical impact of these therapies has been disappointing. At the source of the problem is the observation that, once established, respiratory virus disease results from two concurrent pathologic components: ongoing virus replication and the resulting inflammatory response. Even when antivirals clearly inhibit virus replication, the biochemical and cellular inflammatory responses to the initial infection-related events continue despite diminished virus titer. Prolonged inflammation has been recognized as a significant component contributing to the pathologic sequelae of RSV and influenza virus, and most recently, to the morbidity and mortality of SARS-CoV infection. Our group has developed and characterized a mouse model of severe, acute respiratory infection using the highly virulent natural rodent pathogen, pneumonia virus of mice (PVM, family Paramyxoviridae, subfamily Pneumovirinae, strain J3666). Mice that are inoculated with fewer than 100 plaque forming units (pfu) develop acute lower airway disease characterized by progression to pneumonia, respiratory failure and death (see previous publications, since 2000). We have previously demonstrated that, analogous to influenza and RSV infection, the chemokine MIP-1a is central to this virus-induced inflammatory process, and that interruption of MIP-1a signaling via the receptor CCR1 results in marked reduction in pulmonary inflammation (J Immunol, 2000). Furthermore, we have shown that the inflammatory events associated with pneumovirus infection are not inextricably linked to ongoing viral replication, as replication blockade with ribavirin does not mitigate the associated inflammatory events contributing to the infection-associated morbidity and mortality (J Virol, 2003). In the first of the two manuscripts reported in this year (ref #1 Altered pathogenesis of severe pneumovirus infection in response to combined antiviral and specific immunomodulatory agents), we reported the responses of mice with symptomatic pneumovirus infection to combined antiviral and specific immunomodulatory agents. Mice infected with pneumonia virus of mice, a natural mouse pathogen that replicates the signs and symptoms of severe infection with respiratory syncytial virus (RSV), responded to the antiviral agent ribavirin when it was administered in the setting of endogenous (gene deletion) or exogenous (antibody-mediated) blockade of the MIP-1alpha proinflammatory signaling cascade. Although neither treatment was effective alone, together they offered a dramatic reduction in symptoms and pathology, the most impressive of which was a significant reduction in morbidity and mortality. The findings presented are consistent with the notion of unique and independent contributions of virus replication and ongoing inflammation to the pathogenesis of severe respiratory virus infection, and they provide the impetus for the study of this treatment regimen in RSV-infected humans. In the second (ref #2 Functional antagonism of chemokine receptor CCR1 reduces mortality in acute pneumovirus infection in vivo) we presented an antiviral-immunomodulatory therapeutic strategy involving the chemokine receptor antagonist Met-RANTES, which yielded significant survival in the setting of an otherwise fatal respiratory virus infection. We demonstrated that ribavirin reduced mortality, from 100% to 10 and 30%, respectively, in gene-deleted CCR1 (-/-) mice and in wild-type mice treated with the small-molecule chemokine receptor antagonist, Met-RANTES. As MIP-1alpha-mediated inflammation is a common response to several distantly related respiratory virus pathogens, specific antiviral therapy in conjunction with blockade of the MIP-1alpha/CCR1 inflammatory cascade might ultimately prove to be a useful, generalized approach to severe respiratory virus infection and its pathological sequelae in human subjects. We have also authored four major invited reviews on this subject (refs #5, 8, 9 and 13). Methods: PCR RT-PCR Quantitative RTPCR Molecular Cloning Restriction Digestion DNA sequencing Bacterial protein expression expression Baculovirus protein expression Mammalian cell protein expression Adenovirus expression FACS analysis Northern blotting Southern blotting Fast Protein Liquid Chromatography Affinity Chromatography Western blotting Enzymatic assays ELISA Immunoprecipitation Gene microarray Immunohistochemistry
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