Immunological aspects of the acquired B antigen.

Nine cases of acquired B antigen were studied. By quantitative methods the variation of the A reactivity and of the number of A sites was found to be inversely related to the variation of the B reactivity. By agglutination kinetics using an immune anti-B, the acquired B reactive structure was found to differ from that of a normal B. Agglutination variation, with pH, points out to the part played by one electrically charged chemical group. No transferase galactosyl activity was found in the serum, and no B substance in the plasma. According to these results the B reactive structure must have been formed at the expense of the A reactive structure. This "acquired B" type may have arisen as a result of the action of a bacterial deacetylase, transforming the A reactive N-acetyl galactosamine into galactosamine.