Murine cytomegalovirus genomic material in marrow cells: Relation to altered leukocyte counts during sublethal infection of mice

To investigate infection of hematopoietic cells by murine cytomegalovirus (MCMV), we used in situ hybridization to detect MCMV genomic material in marrow cells during sublethal infection of three-week-old mice. MCMV genomic material was present in femoral marrow cells on days 3, 5, 7, and 14, and detection of MCMV genomes correlated strongly with recovery of infectious virus. Peak infection occurred on day 5, when 0.003%-0.185% of the marrow cells contained MCMV genomic material. At peak infection, MCMV genomic material was observed predominantly in marrow mononuclear cells. Coincident with marrow infection, mice experienced significant leukopenia, whereas cessation of MCMV replication in marrow cells was associated with leukocytosis and restoration of normal peripheral blood leukocyte counts.