Measles virus replication in cells of myelomonocytic lineage is dependent on cellular differentiation stage

Measles virus (MV)-infected monocytes may have a central role in virus-induced immunosuppression. Our understanding of MV replication in monocytic cells is, however, incomplete. In this work we have investigated MV replication in cells of human myelomonocytic lineage with different maturation stages in order to study the effect of cellular maturation on virus infection. MV was able to infect human bone marrow myeloid granulocyte-macrophage colony-forming cells (CFC-GM) as well as monocytes and macrophages, but the replication cycle seemed to be regulated by the maturation stage of the cells. Virus infection in CFC-GM was productive, unlike in monocytes and macrophages, where an extensive viral RNA synthesis occurred and high amounts of proteins were synthesised without a remarkable release of infectious virus. Efficiency of viral macromolecular synthesis in macrophages was comparable to that of promonocytic cell line U-937 and human epithelial cell line A549, but in contrast to macrophages the cell lines highly supported productive infection. On the other hand, chemically induced maturation of the human promyelocytic and promonocytic cell lines HL-60, THP-1, and U-937 to more mature macrophage-like forms did not markedly alter the replication cycle of MV in these cell lines. Our results showed that MV replication in myelomonocytic cells varied depending on the maturation stage of the cells. The immature myelomonocytic cells supported productive virus infection, but the maturation process lead to cellular changes that caused a restriction of MV replication cycle partly at posttranscriptional and partly at posttranslational level. The metabolic milieu of monocytes and macrophages as such was sufficient to support extensive viral macromolecular synthesis.