Immunological evaluation of Vi-CPS-BSA conjugate of Salmonella typhi

Abstract number: 1733_573

Ahmadi H., Tabaraiee B., Siadat S., Poor Mirza Gholi F., Norouzian Shamasbi D., Hedayati M.

Introduction: The role of Vi-capsular polysaccharide (Vi-CPS) in human immunity against infection caused by Salmonella typhi is well known. Purified Vi-CPS can be regarded as a reliable immunogen to control typhoid fever in man. Moreover BSA can be selected as a T-dependent macro-carrier protein in order to conjugate with Vi-CPS.

Methods: Vi-CPS was extracted from standard strain of Salmonella typhi Ty6s (CSBPI-B-191) according previously described, by Ahmadi et al, 1999. The Vi-CPS of Salmonella typhi Ty6s was conjugated to Bovine Serum Albumin (BSA-Sigma) according to Mattox et al, 1989. The conjugate was prepared with 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDAC). The conjugate, Vi-CPS and BSA were injected intramuscularly into three group of three rabbit with boosters on days 15, 30 after the primary immunisation. The serum collected on days 0, 15, 30, 45 and 180 were tested by Passive Hemaglutination test for evaluation of antibody production responses in rabbit model.

Results: In comparison purified Vi-CPS with Vi-CPS-BSA conjugate, the titer of hemagglutination passive of anti Vi-CPS-BSA conjugate was 512 which shows 30 times increase in titer when 3 I/M injection of 50 mg of conjugate were given to animals.

Discussion: This finding reveals that I/M injection of covalently bound purified Vi-CPS to a T-dependent proteins elicited much higher levels of antibodies than Vi-CPS alone besides, this conjugate it induce a booster responses in human. But, unfortunately the level of conjugation in this process is low due to les number of protein binding sites on Vi-molecules.

Though the Vi-CPS conjugates elicits higher levels of antibodies, immunoprophylactic activities of the conjugate must be as curtained by clinical evaluation and more research should be conducted to increase the degree of conjugation of the two macromolecules.