Quantitative analysis of IgG class and subclass and IgA serum response to Shigella sonnei and Shigella flexneri 2a polysaccharides following vaccination with Shigella conjugate vaccines

It has been recently reported that a conjugate vaccine composed of the O-sp ecific polysaccharide of S, sonnei bound to Pseudomonas aeruginosa recombin ant exoprotein A (rEPA) conferred 74% protection against S. sonnei shigello sis. In the present study affinity purified Shigella antibodies were used a s standards to quantify and characterize the serum antibody response to vac cination with Shigella sonnei or Shigella flexneri 2a polysaccharide conjug ated to rEPA. The geometric mean concentrations of antibodies at the pre-va ccination stage were 3.8 mu g/ml for IgG anti-S. sonnei LPS and 11.26 mu g/ ml for IgG anti-S. flexneri 2a LPS, Vaccination with S. sonnei-rEPA and S. flexneri 2a-rEPA induced the production of specific IgG antibodies to level s of 115.8 mu g/ml and 126.5 mu g/ml, respectively. The levels of specific antibodies above the pre-vaccination values persisted for at least 2 years. The IgG response to S. flexneri 2a-rEPA conjugate was almost entirely repr esented by the IgG2 subclass. The concentration of IgG1 anti-S. sonnei LPS was significantly higher than that of IgG2 14 days after vaccination with t he homologous conjugate, but decreased to similar levels to those of IgG2 6 , 12 and 24 months after immunization. Since the only difference between th e S, sonnei and S. flexneri 2a conjugates lies in the different polysacchar ides of the two Shigella serogroups (the protein rEPA, is identical in both cases), it follows that the different pattern of IgG subclass response is a result of the different structures of the two O-polysaccharides of S, son nei and S. flexneri 2a. (C) 1999 Elsevier Science Ltd, All rights reserved.