Improved survival after pneumococcus in splenectomized and nonsplenectomized mice with Corynebacterium parvum

Splenectomy increases the susceptibility to infections with certain bacteria, particularly Streptococcus pneumoniae. Because the immunomodulator Corynebacterium parvum expands the phagocytic cell compartment and enhances reticuloendothelial function, we tested the effect of C parvum in mice challenged with aerosolized pneumococci. Mice splenectomized seven days before pneumococcal challenge and treated intraperitoneally with 700 micrograms of C parvum immediately after exposure were protected when compared with splenectomized or sham-operated saline-injected controls. Analysis of proportional hazards showed the risk of dying in order of greatest to least as follows: splenectomy/saline, sham/saline, splenectomy/C parvum and sham/C parvum. The benefits of an intact spleen and C parvum seemed to be additive in their protective effects after aerosol pneumococcal challenge. After intravenous challenge, bloodstream clearance was improved in sham-operated mice at three days after C parvum injection compared with saline-injected sham-operated controls and C parvum-injected splenectomized mice. A significant improvement in bacterial clearance did not occur until seven days after C parvum treatment in splenectomized mice. The results demonstrate the value of a nonspecific immunomodulator for enhancing the defense mechanisms of both normal and splenectomized animals.