Calcium requirement for syncytium formation in HEp-2 cells by respiratory syncytial virus

Respiratory syncytial virus (RSV) grown in HEp-2 cells in the absence of calcium did not induce cell fusion and syncytium formation. Although the infected cells contained viral antigens, the cytopathic effect (giant cell formation) typical for RSV was not observed in calcium-free cultures. Infectious virus yield was also slightly reduced (less than a one log₁₀ reduction) in the absence of calcium. An analysis of viral proteins synthesized in both the presence and the absence of calcium revealed that the amount of fusion protein (F₁) in calcium-free infected cultures was approximately one-third that in calcium-containing infected cultures. These results underscore the necessity of using calcium-containing growth medium for cell culture isolation and diagnosis of RSV.