MyD88-dependent pro-inflammatory activity in Vi polysaccharide vaccine against typhoid promotes Ab switching to IgG

Vi capsular polysaccharide is currently in use as a vaccine against human typhoid caused by Salmonella Typhi. The vaccine efficacy correlates with IgG anti-Vi Abs. We have recently reported that Vi can generate inflammatory responses through activation of the TLR2/TLR1 complex. In the present study, we show that immunization with Vi produces IgM as well as IgG Abs in wild type mice. This ability is not compromised in mice deficient in T cells. However, immunization of mice lacking the TLR adaptor protein, MyD88, with Vi elicits only IgM Abs. These results suggest that MyD88-dependent pro-inflammatory ability of the Vi vaccine might be vital in generating IgG Abs with this T-independent Ag.