Studies on human KC cell syncytia formation induced by Mason-Pfizer monkey virus

Human KC cell monolayer inoculated with concentraten Mason-Pfizer monkey virus (MPMV) showed syncytia formation within an hour. The cell fusion was blocked by the treatment of the MPMV with neutralizing antiserum. Treatment of the MPVM with beta-propiolactone resulted in the loss of infectivity although KC cell fusion ability of the virus still remained. KC cells inoculated with unconcentrated MPMV showed no cell fusion even after several transfers, although a chronic MPMV infection was established. The virus-producing KC cells were refractory to fusion by MPMV. Human embryonic lung cells (HEL) were infected by serially diluted MPMV harvested from virus-producing culture, transferred twice, then cultivated together with KC cells for syncytia formation to examine the end point dilution titer of the virus. HEL infected by 10(-4)-diluted MPMV still induced syncytia formation by cocultivation with KC cells.