Murine influenza virus encephalomyelitis. III. Effect of defective interfering virus particles.

Defective interfering influenza virus particles lessened the yield of infective virus recovered from brain after intracerebral challenge of 3-week old mice, but failed to affect the appearance of disease or lethality. In 7-week old mice, the presence of defective interfering influenza virus particles reduced both lethality and virus yield. Viral inocula containing significant numbers of defective particles appeared to diminish later inflammatory changes, nerve cell degeneration and the appearance of viral antigen in deeper cerebral regions. The protective effect exerted by defective virus particles does not appear related to interferon production in brain.