The presence of Moloney virus induced antigen on antibody-producing cells.

Mice infected at birth with Moloney virus were stimulated with an unrelated antigen (sheep red blood cells) during the lag period before the outbreak of leukaemia. Their spleen cell suspensions were incubated with anti-Moloney serum and complement before plating by the Jerne technique. This treatment—compared with incubation with normal serum and complement—caused a decrease in number of plaque forming cells in one-fourth of the infected mice, indicating that their antibody producing cells contained virus specific surface antigen.