Characterization and Quantitative Analysis of Serum IgG Class and Subclass Response toShigella sonneiandShigella flexneri2a Lipopolysaccharide following NaturalShigellaInfection

The IgG subclass response to Shigella sonnei and Shigella flexneri 2a lipopolysaccharide (LPS) was examined in subjects naturally exposed to these organisms. Affinity-purified LPS antibodies obtained using a column of Shigella LPS bound to epoxy-activated Sepharose 6B were used as standards to calibrate the serum antibody response to natural Shigella infection. The geometric mean concentrations of specific IgG in sera from those not exposed to Shigella organisms were 7.9 microg/mL against S. sonnei LPS and 18.6 microg/mL against S. flexneri 2a LPS. After natural exposure to S. sonnei or S. flexneri 2a, the concentrations rose to 30.3 and 127.9 microg/mL, respectively. IgG2 was the major component in the anti-S. flexneri subclass response, while the anti-S. sonnei response was dominated by IgG1. High levels of IgG1 antibodies before exposure to organisms from either Shigella serogroup correlated with a lower risk of developing symptomatic infection.