Influenza viruses are common and highly infectious human pathogens. They are constantly mutating to modify their antigenicity and avoid elimination by immunity to previous generations of virus. The nucleoprotein of influenza B virus is a basic, phosphorylated multimeric protein consisting of 560 aa subunits that encapsidate the viral RNA genome to form a ribonucleoprotein particle. This antibody reacts with influenza B virus nucleoprotein in immunoblotting. The antibody does not cross-react with influenza A virus.