Early clearance of pneumococci from the lungs of decomplemented rats

Pneumococcal types which exhibited varying degrees of interaction with the complement system in vitro wee aerosolized into normal and decomplemented rats, and the rate of killing of pneumococci was monitored by serial cultures of whole lung homogenates. The clearance of pneumococci from the alveoli did not correlate with the ability of the pneumococci to be opsonized by complement in vitro. Similarly, rats depleted of complement in the serum and the bronchoalveolar lavage fluid maintained their ability to rapidly inactivate aerosolized pneumococci. These results indicate that the early phase of pneumococcal killing in the alveoli does not require complement and suggest that in the nonimmune host, phagocytosis by alveolar macrophages can be achieved without complement-dependent opsonization or, alternatively, that extracellular factors rapidly inactivate inhaled pneumococci.