Toxicity of Lipopolysaccharide and of Soluble Extracts of Salmonella Typhimurium in Mice Immunized with a Live Attenuated AroA Salmonella Vaccine

Mice immunized intravenously 10 days earlier (but not those immunized 2 months earlier) with an attenuated Salmonella typhimurium SL3261 aroA live vaccine and tested for delayed-type hypersensitivity by injection of crude Salmonella extracts in the footpad can die within 24 to 48 h of an unexplained allergic reaction. The lethal reaction could be prevented by prior administration of anti-tumor necrosis factor alpha serum. Injection of lipopolysaccharide (LPS) (either purified phenol-water-extracted [Westphal] LPS or protein-rich trichloracetic acid-extracted [Boivin] LPS) was also lethal for mice immunized 10 days before. An LPS-rich crude Salmonella extract was more toxic than one which contained less LPS, suggesting that LPS may have been involved in the lethal reactions to crude antigens. Mild alkaline hydrolysis removes O-linked acyl groups from lipid A and eliminates many toxic effects of LPS; however, both Boivin LPS and Westphal LPS remained toxic for immunized mice after alkaline hydrolysis. In contrast, alkaline hydrolysis of crude whole Salmonella extracts (which caused marked protein degradation) reduced the lethal toxicity of the extracts, especially for an LPS-rich preparation. Mice immunized orally with the live vaccine did not show hypersensitivity to either LPS or crude extracts. The results suggest that the lethal reaction to crude Salmonella antigens in mice immunized 10 days earlier is complex, that tumor necrosis factor alpha is involved, and that allergic reactions to crude antigens (but not to LPS alone) can be reduced by mild alkaline hydrolysis.