Effect of Alkali on the Immunological Reactivity of Lipopolysaccharide from Salmonella typhimurium.

The effect of mild alkaline hydrolysis on the immunological reactivity of Salmonella typhimurium lipopolysaccharide (LPS) was studied. Hydrolysis of LPS at 37 C in 0.01 to 0.25 n NaOH caused a decrease in precipitation of LPS by antiserum. Red cells sensitized with alkali-treated LPS were less responsive to hemagglutination by antiserum than were cells sensitized with heated LPS. Hemagglutination-inhibition studies showed that alkali-treated S. typhimurium LPS was antigenically deficient. Alkaline hydrolysis of S. typhimurium LPS destroys antigen 5 of the Kauffmann-White scheme by cleavage of O-acetyl groups. However, abequose, the immunodominant sugar for antigen 4, is also cleaved from the O side chains by alkali, suggesting the loss of more than one antigenic determinant. It is concluded that alkali treatment of LPS to promote the sensitization of red cells may alter the serological specificity and therefore places limitations on its use in serological studies.