The role of the spleen in experimental pneumococcal bacteremia

The importance of the spleen in host defense against pneumococcal bacteremia has been suggested by a number of experimental models as well as the occurrence of the syndrome of overwhelming pneumococcal sepsis in asplenic individuals. We studied the mechanism of splenic protection against pneumococcal bacteremia using a guinea pig model. Rates of removal of pneumococci from the blood stream in normal and splenectomized guinea pigs were compared with the extent of hepatic and splenic sequestration of radiolabeled organisms for three different types of pneumococci. A relationship was found between the virulence of a pneumococcus for normal guinea pigs, the extent to which it is cleared by the spleen, and the magnitude of the defect in blood stream sterilization induced by splenectomy. The spleen plays an increasingly important role in the clearance of progressively more virulent organisms, for which hepatic clearance cannot compensate. Thus, the division between hepatic and splenic clearance of bacteremia is a key determinant of the outcome of experimental pneumococcal infection.