Shigella lipopolysaccharide antibodies in pediatric populations

Shigellosis is the most common cause of bacterial dysentery. To study the specific immunity to the two major groups causing shigellosis, we assayed antibodies to lipopolysaccharide (LPS) by enzyme-linked immunoadsorbent assay to both Shigella sonnei and Shigella flexneri 2a serotypes in the following populations: (1) women immediately after delivery and their infants to assess the transfer of passive immunity by placenta and the presence of secretory antibodies in breast milk; (2) children of different ages; and (3) the kinetics of antibody production in pediatric patients, who had culture-proved shigellosis. The sera of these women showed variable concentrations of antibodies of all three isotypes to LPS of S. sonnei and S. flexneri 2a. These serotype-specific antibodies were not cross-reactive. Transfer of IgG anti-LPS across the placenta was significantly correlated with concentration of the specific antibody in the mother (S. sonnei, r = 0.96; S. flexneri, r = 0.84). Varying concentrations of anti-LPS IgA were present in colostrum, which was correlated with serum anti-LPS IgA titers in the case of S. sonnei (r = 0.44; P < 0.05) but not S. flexneri (r = 0.17). Healthy children between the ages of 6 months and 4 years in our population had undetectable or relatively low titers of anti-S. sonnei IgG. More children had detectable antibody titers to S. flexneri 2a than to S. sonnei. The relatively high concentrations of these natural antibodies are particularly noteworthy because there is a far lower incidence (< 10% of patients) with S. flexneri than with S. sonnei disease in this population. Determination of antibody titers from 15 patients, all of whom had S. sonnei infection, showed an increase in IgM and IgG antibody concentration in their convalescent sera. Therefore we speculate that the presence of anti-LPS IgG correlates with protection from shigellosis in pediatric populations.