The characterization of monoclonal antibodies to human metapneumovirus and the detection of multiple forms of the virus nucleoprotein and phosphoprotein

Little is known of the proteome of human metapneumovirus (HMPV). In this study a panel of monoclonal antibodies to the virus have been characterized and used to identify viral proteins present in infected cell lysates. Of thirteen anti‐HMPV monoclonal antibodies four reacted with recombinant fusion glycoprotein and one with recombinant G glycoprotein by immunofuorescence but not in western blots suggesting that they recognize conformation dependent epitopes. The specificity of the remaining antibodies were determined by MALDI/TOF analysis of the proteins they immunoprecipitated from HMPV infected cell lysates and by western blotting. Five MAbs bound to the nucleoprotein and three to the phosphoprotein. In western blots of lysates of cells infected with low passage HMPV, the anti‐nucleoprotein MAbs stained a single polypeptide corresponding in size to the full length nucleocapsid protein. On repeated passage of the virus in cell culture, however, a second, smaller band appeared which may result from internal initiation of translation within the nucleocapsid gene as described for avian metapneumovirus. Antibodies to the phosphoprotein, besides the full length form, also recognized multiple polypeptides in infected cell lysates, with patterns differing for the two subtypes A and B. The possibility that these too may derive by internal initiation of translation is discussed. J. Med. Virol. 84: 1061–1070, 2012. © 2012 Wiley Periodicals, Inc.