An immunogenic complex of alkali-treated lipid A and methylated bovine serum albumin

Alkali-treated lipid A prepared by hydrolysis of lipid A in 0.25 N NaOH (1 h, 56 degrees C) formed an insoluble complex with methylated bovine serum albumin (MBSA) in aqueous medium. At a 1/1 (w/w) lipid A/MBSA ratio, nearly all lipid A was insolubilized. The complex was assumed to be ionic in nature. On intravenous immunization of rabbits with the complex, antibodies directed against lipid A were elicited. The antibody titres ranged from 1/256 to 1/2,048, as demonstrated by the passive haemolysis test, and proved to be mainly of the IgM class.