Anti-Influenza B Virus Nucleoprotein Antibody (8C8). Influenza virus is an RNA virus, which causes influenza, and belongs to the family Orthomyxoviridae. Influenza virus is classified into three different genera, influenza virus A, B, and C. The central core of the virion contains the viral RNA genome, which is packaged in the form of ribonucleoprotein complexes. Influenza virus nucleoprotein (NP) is a major component of the ribonucleoprotein complex and is abundantly expressed during the course of infection. It is a structural protein, which encapsidates the negative strand viral RNA and is essential for RNA transcription, replication and packaging. From the nucleotide sequence, NP consists of 560 amino acids with calculated molecular mass of 61,770 Da.