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The comparative histopathology of primary and secondary lesions in murine salmonellosis
Abstract:
In a primary infection, Swiss-Webster mice were injected i.p. with 10(2) or 10(3) virulent Salmonella typhimurium. Multiple microscopic acute abscesses with predominantly polymorphonuclear leucocytes (PMNs) were seen in the liver and the spleen beginning on the 4th day after infection. By the 7th day, these lesions had become enlarged and were gradually transformed into granulomas with central necrosis and peripheral mononuclear cells. The animals usually died within 12 days with massive systemic infection and degeneration of the tissues. In contrast, it was necessary to inoculate 10(6) virulent salmonella i.v. into mice immunized with avirulent S. thphimurium in order to initiate microscopically observable lesions in the liver and the spleen. These secondary lesions were characterized by the early appearance of minute granulomas composed almost entirely of histiocytic cells. They remained small and isolated, usually without central necrosis. Subsequent regression of the lesions and regeneration of normal tissue occurred after the 2nd week following infection. The animals usually survived such a challenge infection.
Insights
Primary Salmonella typhimurium infection caused acute abscesses and death in mice. Prior immunization with avirulent Salmonella protected mice, leading to smaller lesions and survival.
Area of Science:
- Immunology
- Microbiology
- Pathology
Background:
- Salmonella typhimurium infection in mice leads to acute abscesses and systemic disease.
- Understanding the immune response to Salmonella is crucial for developing effective treatments.
Purpose of the Study:
- To compare the pathological outcomes of primary and secondary Salmonella typhimurium infections in mice.
- To investigate the role of prior immunization in modulating the host response to Salmonella.
Main Methods:
- Swiss-Webster mice were infected with virulent Salmonella typhimurium via intraperitoneal injection.
- A separate group of mice was immunized with avirulent S. typhimurium before challenge with virulent bacteria.
- Histopathological analysis of liver and spleen tissues was performed at various time points post-infection.
Main Results:
- Primary infection resulted in acute abscesses, granuloma formation with necrosis, and high mortality within 12 days.
- Immunized mice required a higher inoculum of virulent Salmonella to develop lesions.
- Secondary lesions were characterized by smaller granulomas, predominantly histiocytic cells, and absence of central necrosis.
- Lesions in immunized mice regressed, with tissue regeneration and survival.
Conclusions:
- Prior immunization significantly alters the host immune response to Salmonella typhimurium.
- Immunization confers protection against virulent Salmonella, characterized by attenuated pathology and improved survival.
- The study highlights the potential of avirulent strains in developing Salmonella vaccines.