Mechanisms of lipopolysaccharide-induced protection against pseudomonas sepsis in granulocytopenic mice.

The nature of the enhanced resistance to Pseudomonas aeruginosa sepsis induced by type-specific lipopolysaccharide vaccine was examined in a mouse model of cyclophosphamide-induced granulocytopenia. Mice actively immunized with type-specific vaccine survived significantly longer than did nonimmune mice (P less than .002) when challenged 8, 12, or 16 days after immunization. This protection was nonspecific eight days after immunization and specific 12 days after immunization. Passive immunization of mice with specific antibody resulted in significant, though minimal, protection. In contrast, long-term protection was observed when the passive transfer of specific antibody was combined with nonspecific immunization. This observation suggests that the specific protection observed with type-specific active immunization results from the interaction of specific antibody and an immunization-induced nonspecific cellular effector. While no significant effect of immunization on granulocyte counts in peripheral blood was demonstrated, studies of phagocytosis performed with peritoneal mononuclear cells suggest that the macrophage may be the immunization-induced, nonspecific cellular effector.