Effect of passive antibody on parainfluenza virus type 3 pneumonia in hamsters.

Both parainfluenza virus type 3 and respiratory syncytial virus may produce life-threatening pneumonia or bronchiolitis in infants less than 6 months old. Almost all infants in this age group possess passively acquired maternal antibodies to both viruses. It has been suggested that maternal antibodies may actually participate in the pathogenesis of these diseases in early infancy. This investigation examined the effect of moderate levels of passive antibody on the development of pneumonia in hamsters infected intranasally with parainfluenza virus type 3. The pneumonitis produced in this model was not enhanced by the presence of moderate levels of serum antibody to this virus. Furthermore, reinfection after an initial "sensitizing" infection under the cover of passive antibody did not result in a more severe pneumonitis. These studies do not support either of the two hypotheses that have been advanced to explain the pathogenesis of infections with respiratory syncytial virus in early infancy.