Cellular immunity induced by avirulent Salmonella in LPS-defective C3H/HeJ mice.

An avirulent strain of Salmonella, SL3235, has been shown to confer high levels of immunity on lipopolysaccharide (LPS)-hyporesponsive C3H/HeJ mice. Immunized mice were also protected against challenge with Listeria monocytogenes, indicating that the Salmonella vaccine activates macrophages. It was shown that protection and macrophage activation occurred without correction of the LPS defect, as assessed by in vivo endotoxin toxicity, in vitro spleen cell mitogenicity, and the ability of in vivo treatment with LPS to enhance in vitro macrophage ingestion of C3b-coated erythrocytes. It is concluded that LPS responsiveness is neither a necessary nor a sufficient condition for Salmonella immunity, and that macrophage activation can apparently occur in C3H/HeJ mice in the face of a sustained LPS defect.