SYNTHESIS, CHARACTERIZATION, AND IMMUNOLOGICAL PROPERTIES IN MICE OF CONJUGATES COMPOSED OF DETOXIFIED LIPOPOLYSACCHARIDE OF SALMONELLA-PARATYPHI-A BOUND TO TETANUS TOXOID, WITH EMPHASIS ON THE ROLE OF O-ACETYLS

Salmonella paratyphi A, the second most common cause of enteric fever in Southeast Asia, is a habitant of and a pathogen for humans only. Li popolysaccharides (LPS) are both essential virulence factors and prote ctive antigens for systemic infections caused by groups A, B, C, and D nontyphoidal salmonellae. The O-specific polysaccharide of S. paratyp hi A is composed of a trisaccharide, p-(1-->4)-alpha-L-Rhap-(1-->3)-al pha-D-Galp-(1-->, with a branch of D-paratose from the C-3 of alpha-D- mannose, and the C-3 of beta-L-rhamnose is partially O acetylated (C. G. Hellerqvist, B. Lindberg, K. Samuelsson, and A. A. Lindberg, Acta C hem. Scand. 25:955-961, 1971). On the basis of data from our investiga tional vaccines for enteric bacterial pathogens, including group B sal monellae (D. C. Watson, J. B. Robbins, and S. C. Szu, Infect. Immun. 6 0:4679-4686, 1992), conjugates composed of the detoxified LPS of S. pa ratyphi A bound to tetanus toxoid (TT) were prepared by several scheme s. LPS was detoxified with acetic acid or with hydrazine; the latter r emoved O acetyls from the O-specific polysaccharide. The detoxified po lysaccharides were activated with cyanogen bromide (CNBr) or with 1-cy ano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) and bound to TT with or without a spacer. Solutions of 2.5 mu g of saccharide, alone or as a conjugate, were injected subcutaneously into young mice, and L PS and TT antibodies were measured by enzyme-linked immunosorbent assa ying. A conjugate synthesized with higher-molecular-weight O-SP elicit ed the highest anti-LPS levels. Only conjugates with O acetyls elicite d serum immunoglobulin G anti-LPS with bactericidal activity. There we re no statistically significant differences between LPS antibody level s elicited by conjugates synthesized with or without a spacer. The con jugate with O-specific polysaccharide activated by CDAP and bound to T T without a spacer elicited the highest level of TT antibodies. Clinic al evaluation of S. paratyphi A conjugates is planned.