Subclass characterization of IgG anti-S.typhi lipopolysaccharide antibodies with commercial monoclonal antibodies

We have evaluated several commercial monoclonal antibodies, specific for human IgG subclasses, for their reactivity in an ELISA test for the characterization of subclasses of IgG anti- Salmonella typhi lipopolysaccharide (LPS) antibodies. Four monoclonals, each specific for a single IgG subclass, were chosen for their good reactivity. In 19 typhoid and non-typhoid serum samples, the sum of the ELISA values obtained with the four subclass-specific monoclonals was highly correlated with the ELISA values obtained with a monoclonal anti-total IgG. Moreover, there was no competition among the various IgG subclasses of anti-LPS antibodies. These data indicate that the subclass distribution of IgG anti-LPS antibodies, calculated on the basis of ELISA values in the subclass-specific assays, is likely to reflect the actual distribution of the different subclasses in whole serum. Different subclass patterns of IgG anti-LPS antibodies were observed in serum samples from 11 patients with typhoid fever, with IgG1 and IgG2 being the most represented subclasses. The ELISA method described here will be useful to elucidate the factors that influence the anti-LPS subclass profile during the humoral immune response to Salmonella typhi.