Immunochemistry of <i>Salmonella</i> O-Antigens

Abstract

The binding specificities of antibodies directed against the <i>Salmonella</i> sero-group A-specific O-antigen 2 determinant were characterized by precipitation-inhibition and enzyme-linked immunosorbent assay inhibition tests. Two different antigen O-2-specific antisera were investigated: one conventional factor O-2-serum (elicited by whole heat-killed <i>Salmonella paratyphi</i> A bacteria) and another elicited by the synthetic disaccharide 3-<i>O</i>-α-paratopyranosyl-<i>D</i>-mannopyranosyl (Par<i>p</i>13/α D-Man<i>p</i>) covalently linked via a <i>p</i>-isothiocyanatophenyl aglycon to bovine serum albumin (PM-BSA). The inhibition data showed that factor O-2 antibodies have combining sites which recognize structures larger than the Par<i>p </i>13/α D-Man<i>p</i> disaccharide and equal to or smaller than an O-antigen O-2-specific octa-α saccharide derived from the <i>S. paratyphi</i> A O-polysaccharide. Although the factor O-2 serum exhibited a high specificity for the homologous <i>S. paratyphi</i> A O-antigen it still precipitated, though weakly, a heterologous <i>Salmonella typhimurium</i> O-antigen. In contrast, anti-PM-BSA antibodies were exclusively specific for the O-2 determinant of the native polysaccharide antigen. The combining sites of these antibodies best recognized the Par<i>p </i>13/α D-Man<i>p</i> disaccharide, including the linkage arm and the lysyl residue of the BSA carrier protein molecule. These data extend earlier findings as to the superior specificity of anti-PM-BSA antibodies as compared to conventional factor O-2 antibodies.