B cell ICAMs are required for effective B cell competition in polyclonal immune responses. (A) Representative flow cytometric plots of GC and follicular compartments composition in popliteal LNs of chimeric hosts (∼50% IC-1/2^+/+ and ∼50% IC-1/2^−/− B cells) 14 d after infection with VSV. IC-1/2^+/+ B1-8^hi B cells were gated as CD45.1⁺, and IC-1/2^−/− B1-8^hi B cells were gated as ICAM-2⁻ and CD45.1⁻. The graph shows the percentage of B cells in the GC (FAS⁺ CD38^low) normalized to the follicular B cell compartment (FAS⁻ CD38^high). Data are pooled from two independent experiments with a total of 10 mice per group. (B) Analysis of chimeric mice as in A that were immunized with NP-OVA. IC-1/2^+/+ B1-8^hi B cells were gated as CD45.1⁺, and IC-1/2^−/− B1-8^hi B cells were gated as CD45.2⁺. Data are pooled from two independent experiments with a total of five mice per group. (C) Analysis of the proportion of each cell type in GCs in Peyer’s patches of chimeric mice. Data are pooled from two independent experiments with a total of eight mice per group. (D) Analysis of the GC composition in chimeric mice hosting either IC-1/2^+/+ or IC-1/2^−/− B cells. Gated as CD8⁻, CD4⁻, F4/80⁻, GR-1⁻ (dump) and B220⁺. Data are pooled from two independent experiments with a total of six to eight mice per group. Each dot in the graphs represents a single mouse; lines represent the mean. (E) Titers of total (NP₂₀) and high-affinity (NP₄) anti-NP IgG in serum of NP-OVA immunized chimeric mice. (F) Ratios of high-affinity/total anti-NP antibodies. Pooled data from two experiments with total of four to five mice in each group. *, P = 0.05; ***, P < 0.0001; ns, not significant; two-tailed Student’s t test.