Serum immunoglobulin titers in immunized sera were separately measured against each component OMVs of bivalent OMV and heat-killed (HK) formulations.

ELISA plates were coated with either each component of OMVs or heat-killed immunization and either bivalent immunized mice serum or heat-killed immunized mice serum was used, at appropriate times. While doing ELISA against Vi-polysaccharide, ELISA plates were coated with market-available Vi-polysaccharide. A. Serum IgG (i), IgG1 (ii), IgG2a (iii), IgG3 (iv); B. Serum IgA; C. Serum IgM; D. Anti-Vi serum IgG; E. sIgA; F. i. ii. Serum IgG1 and IgG3 response against each of the two OMVs, Salmonella Typhi and Paratyphi A, respectively at pre-immunization, immunization and post-immunization periods. High serum IgG3 titer against IgG1 indicates higher Th1 cell-mediated immune response in adult mice sera after three doses of immunization. The horizontal axis indicates the days of blood collection. Data represented here are the mean values +/- Standard Deviation (SD) of three independent experiments. No statistically significant difference in overall antibody response was observed against each of the two OMVs (P values >0.05). The differences in post-immunization day wise response of each of the studied antibodies against each of the two OMVs were highly significant (P value< 0.005).