Patients without a spleen are susceptible for overwhelming sepsis with Streptococcus pneumoniae. We investigated the relative contribution of the pneumococcal capsule in the reduced host defense after splenectomy. Sham-operated or splenectomized mice were inoculated with serotype 2 or 4 S. pneumoniae (D39, TIGR4) or the isogenic nonencapsulated mutants (D39Δcps, TIGR4Δcps). After splenectomy, intranasal infection with D39 resulted in increased mortality, increased bacterial dissemination and exaggerated systemic inflammation rather then altering inflammation in the lungs. Intravenous infection also resulted in enhanced mortality, bacterial growth and systemic inflammation after splenectomy. In contrast, the spleen did not contribute to host defense during infection with D39Δcps. Similar observations were made for TIGR4: increased bacterial growth and inflammation after intravenous infection with wild-type, but not nonencapsulated bacteria in splenectomized mice. These results indicate that the capsule of S. pneumoniae is indeed responsible for increased vulnerability of asplenic mice to invasive pneumococcal disease.
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