Measles virus infection of unstimulated blood mononuclear cells in vitro: antigen expression and virus production preferentially in monocytes.

Synthesis of measles virus antigens occurred only in a small percentage of peripheral blood mononuclear cells infected in vitro with measles virus without mitogenic stimulation. The infection cycle was restricted as only low amounts of infectious virus were released but all the major structural viral proteins were present as shown by immunofluorescence with monoclonal antibodies. Cells with viral antigen synthesis were characterized by double labelling and by infecting selectively depleted subpopulations. In 3-day cultures, up to 80% of the cells with measles virus antigen were shown to be monocytes by specific staining with anti-MMA and anti-Leu M3 monoclonal antibodies and up to 40% of the monocytes were infected. Less than 10% of the cells expressing virus antigens carried the lymphocyte marker OKT3, the majority of these cells belonging to the Leu3a (helper) population. Anti-alpha-interferon treatment increased the number of measles-positive cells and the release of infectious virus in preparations enriched for monocytes, but had no significant effect on infection of lymphocytes.