Serum anti-NP responses to unsialylated (−; NP–PA) or natively sialylated (+; NP–PA–NeuGc) compounds. (A–C) Responses of (A) wild-type, (B) CD22^−/−, and (C) Siglecg^−/− mice. Anti-NP titers were assessed on days 7 and 14 as indicated. (top) IgM anti-NP titers; (bottom) IgG3 anti-NP titers. Each point represents the response of an individual mouse of the indicated genotype. Results shown are representative of at least two independent experiments. Horizontal bars represent means. *, P < 0.05; and ***, P < 0.005 using the two-tailed Student’s t test. n.s., not significant.