Immunization with R mutants of Salmonella minnesota. II. Serological response to lipid A and the lipopolysaccharide of Re mutants.

Rabbits were immunized with Salmonella minnesota Re mutant bacilli or lipid A, and the serological responses were compared. Re lipopolysaccharide and lipid A were found to possess distinct antigenic determinants as measured by hemagglutination, hemolysis, and precipitin techniques. Lipid A preparations from several enterobacterial and non-enterobacterial species were shown to cross-react in agar gel precipitation reactions. In contrast, preparations from bacilli that do not contain glucosamine as an integral part of their lipid A structure did not demonstrate cross-reactivity with enterobacterial lipid A. Antibody to smooth heterologous bacilli present in some antisera prepared against Re bacilli or lipid A was directed specifically against the smooth lipopolysaccharide and not against the Re or lipid A determinants, demonstrating a nonspecific mitogenic response. Precipitation and immunofluorescence tests indicated that the Re determinant was available on smooth bacilli for reactions with specific antisera but that the lipid A determinant was not.