Effect of IgA deficiency on anti-protein and polysaccharide antibody responses following immunization with subunit vaccines. (A-D) Groups of IgA+/+ and IgA−/− mice were immunized with either Fluzone (A), F. tularensis LPS (B), Prevnar (C) or Hib-TT vaccine (D). IgG and IgM anti-protein or polysaccharide antibody levels in sera were determined by ELISA as described in Materials and Methods. Pre-immune IgG and IgM levels in PBS-treated mice are indicated by the dotted line. Each symbol represents an individual mouse and the lines represent the means ± SD with n = 3 to 5 mice per group. *, P < 0.05; **, P < 0.01; t-test with Welch correction. Panels A, C and D show representative data from two to three independent experiments.