Role of granulocytes in experimental Streptococcus sanguis endocarditis

We investigated the role of granulocytes during the induction and course of experimental Streptococcus sanguis endocarditis in rabbits by depleting blood granulocytes with nitrogen mustard. The induction of the endocarditis was not influenced by granulocytopenia: the 50% infectious dose was 5.4 X 10(4) colony-forming units in normal and granulocytopenic rabbits. However, granulocytopenia influenced the curse of the endocarditis, as shown by a significant increase in the number of colony-forming units per gram of vegetation (P less than 0.02) from 24 to 72 h after the injection of 10(5) colony-forming units of S. sanguis. This rise did not occur in the control rabbits. Furthermore, bacteremia was significantly higher in the granulocytopenic rabbits (P less than 0.05) during the first 48 h compared with the control rabbits. This was not because of altered clearance of the streptococcus inoculum or seeding of streptococci from extracardiac bacterial foci. We concluded that granulocytes have no measurable effect on the induction of S. sanguis endocarditis, but during the course of the endocarditis, granulocytes keep the endocardial infection in check.