Efficient B cell proliferation during GC colonization depends on B cell ICAMs. (A) Flow cytometric histograms of CFSE-labeled IC-1/2^+/+ and IC-1/2^−/− B1-8^hi B cells recovered from popliteal LNs 3 and 4 d after immunization with NP-OVA. (B) Quantification of IC-1/2^+/+ and IC-1/2^−/− B cell proliferation among the initially transferred cells (division index) in the experiment shown in A. (C) Quantification of B cell proliferation of cells that divide at least once (proliferation index). Bar graphs represent the mean + SEM of two independent experiments with 10 mice total for each condition or time point. ***, P < 0.001; ns, not significant; two-tailed Student’s t test.