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Effect of splenectomy on the susceptibility of mice inoculated with Diplococcus pneumoniae
Abstract:
An experimental model is described which demonstrated increased susceptibility of mice to infection with D. pneumoniae following splenectomy. It was necessary to use small numbers of a particular strain of pneumococcus (D. pneumoniae type 6), intravenous infection and a particular strain of mouse (pathogen-free NCS strain). The increase in susceptibility persisted for at least 4 months after splenectomy. With modifications in experimental design such as use of large numbers of organisms, a different strain of pneumococcus, the intraperitoneal route of infection or a different mouse strain no increase or a much less impressive increase in susceptibility was demonstrated. Following intravenous injection of small numbers of D. pneumoniae Type 6 bacteremia tended to persist in all NCS mice. Multiplication of pneumococci subsequently occurred in a higher proportion of mice with splenectomy and at a more rapid rate than in control animals. Mice with splenectomy usually had more D. pneumoniae per ml of blood than per gram of any tissue. This suggested that in these mice multiplication of microorganisms occurs primarily in blood. In control mice higher concentrations of bacteria were present in spleen than in blood, and higher concentrations were found in blood than in other tissues. These results suggested that in normal mice infected intravenously with small numbers of D. pneumoniae Type 6, the spleen protects by removing and killing small but critical numbers of D. pneumoniae which are circulating in the blood. No evidence was found to suggest that the altered susceptibility is mediated by an effect of splenectomy on numbers of circulating leukocytes or on the antibacterial activity of mouse blood.
Insights
Splenectomy increases susceptibility to Streptococcus pneumoniae infections in mice, particularly with specific strains and infection routes. The spleen plays a crucial role in clearing pneumococci from the bloodstream.
Area of Science:
- Immunology
- Microbiology
- Pathology
Background:
- The spleen is known to play a role in immune surveillance and clearance of pathogens.
- Understanding the specific contributions of the spleen to host defense against bacterial infections is critical for developing effective treatments.
Purpose of the Study:
- To investigate the impact of splenectomy on the susceptibility of mice to infection with Streptococcus pneumoniae.
- To elucidate the role of the spleen in controlling pneumococcal bacteremia.
Main Methods:
- Development of an experimental model using pathogen-free NCS strain mice and a specific strain of Streptococcus pneumoniae (Type 6).
- Intravenous infection with small numbers of bacteria was employed to assess susceptibility post-splenectomy.
- Bacterial load in blood and tissues was quantified over time in both splenectomized and control mice.
Main Results:
- Splenectomized mice exhibited increased susceptibility to D. pneumoniae infection, with heightened susceptibility persisting for at least 4 months.
- Pneumococcal multiplication occurred more rapidly and in a higher proportion of splenectomized mice compared to controls.
- In splenectomized mice, D. pneumoniae primarily multiplied in the blood, whereas in control mice, the spleen showed higher bacterial concentrations.
Conclusions:
- The spleen is essential for protecting normal mice against low-level intravenous D. pneumoniae infection by removing and killing circulating bacteria.
- Splenectomy impairs the host's ability to control pneumococcal bacteremia, leading to increased susceptibility.
- The spleen's protective mechanism does not appear to be mediated by changes in circulating leukocytes or blood antibacterial activity.