RoleofImmunity inViral-Induced Bacterial Superinfections oftheLung

virus (minimally virulent Mengo-37A anda highly virulent Columbia SK [Col-SK]) toinvestigate these interrelationships. Micethathadbeenimmunized toMengo-37A, andnonimmunizedcontrols, werechallenged withaerosols containing 104plaque-forming units ofMengo-37A orCol-SK perliter. Theeffect ofeachviral infection on pulmonary antibacterial activity was assessed 3dayslater bymeasuring thecapacity ofthe lungs tokill inhaled radiophosphorus (32P)-labeled Staphylococcus aureus.The degree ofantibacterial dysfunction found was proportional tothevirulence ofthe infecting virus. Ifthehost was immunetotheinfecting virus, bactericidal function was notimpaired byviral challenge. Neither mutantcaused significant pulmonary damage; therefore: (i) viral-induced impairment inbactericidal activity reflects, quantitatively, thevirulence ofthevirus and(ii) viral immunity protects pulmonary bacterial defenses bypreventing damagetothephagocyte fromthe virus oritsattendant metabolic abnormalities.