Development of viral antigen and infectious virus were followed in HeLa cells infected with type 1 reovirus. The antigen was found to go through a sequence of four stages determined by shape and intracellular location. Six to eight hours after infection, antigen appeared in particulate form in the cytoplasm. The particles coalesced to form a reticulum-like structure disseminated throughout the cytoplasm; the reticulum in most cases subsequently became perinuclear. In the final stage, the antigen lost much of its reticular structure and spread confluently throughout the cytoplasm. The cytoplasm began “bubbling” and cell processes containing viral antigen constricted and pinched off from the cell.
Cell-associated virus and viral antigen appeared simultaneously after 6 to 8 hr of infection and increased to a maximal concentration at 24 hr. The rate of virus release was slow and appeared to be related to the “bubbling” phenomenon. The effect of the location of antigen and its slow release from the cell may be related to the slow spread of virus in plaques.