αGalCer-activated NKT cells promote antigen-specific antibody production and GC formation. (A-D) B6 or BALB/c mice (n = 5) were immunized intraperitoneally with 40μg NP-KLH (red) or with NP-KLH plus 4 μg αGalCer (black) and analyzed after 9 days. Representative of 3 to 4 independent experiments with 4 to 5 animals per group. (A) Hapten-specific IgG1 titers in the serum of WT B6 and BALB/c mice. (B) Total numbers of B220⁺ GL7⁺ Fas⁺ GC B cells in the spleen of WT B6 and BALB/c animals. (C) Representative immunohistologic and flow cytometry staining of splenic GCs of WT B6 mice. Green: PNA, blue: IgD. (D) Total numbers of GC B cells (B220⁺ GL7⁺ Fas⁺) in the spleen of WT and Jα18^−/− animals (BALB/c). (E) Kinetics of hapten-specific IgG response of WT B6 mice immunized with NP-KLH (red) or NP-KLH plus αGalCer (black). Mice were bled 4, 14, and 29 days after the primary injection, then both groups were challenged with antigen alone on day 30 and were bled 4 and 16 days after. (F) Affinity of NP-specific IgG in immune-sera collected as in (E). (G) B6 mice were immunized with NP-KLH (red) or NP-KLH plus αGalCer (black) and groups of 3 mice were killed at each time point. The number of TCRβ⁺ CD1d TET⁺ NKT cells was determined in the spleen. (H) NP-specific IgM titers in the serum of B6 mice 4 days after immunization with NP-KLH with our without coinjecting αGalCer. (I) The number of plasma cells (PC; CD138⁺B220^int) was determined in the spleen of mice that were immunized as in panel G.