Avian reovirus major mu-class outer capsid protein influences efficiency of productive macrophage infection in a virus strain-specific manner

We determined that the highly pathogenic avian reovirus strain 176 (ARV-176 ) possesses an enhanced ability to establish productive infections in HD-11 avian macrophages compared to avian fibroblasts, Conversely, the weakly pa thogenic strain ARV-138 shows no such macrophagotropic tendency. The macrop hage infection capability of the two viruses did not reflect differences in the ability to either induce or inhibit nitric oxide production. Moderate increases in the ARV-138 multiplicity of infection resulted in a concomitan t increase in macrophage infection, and under such conditions the kinetics and extent of the ARV-138 replication cycle were equivalent to those of the highly infectious ARV-176 strain. These results indicated that both viruse s are apparently equally capable of replicating in an infected macrophage, but they differ in the ability to establish productive infections in these cells. Using a genetic reassortant approach, we determined that the macroph agotropic property of ARV-176 reflects a post-receptor-binding step in the virus replication cycle and that the ARV-176 M2 genome segment is required for efficient infection of HD-11 cells, The M2 genome segment encodes the m ajor mu -class outer capsid protein (muB) of the virus, which is involved i n virus entry and transcriptase activation, suggesting that a host-specific influence on ARV entry and/or uncoating may affect the likelihood of the v irus establishing a productive infection in a macrophage cell.