Reduced competitiveness of GC B cells when ubiquitin-mediated MHCII regulation is defective. (a and b) Mixed BM chimeric mice containing CD45.1⁺ and either I-A^b(K>R) or WT CD45.2⁺ cells were infected with influenza HKx31. The frequency of naive or GC B cells of CD45.2⁺ donor origin in mediastinal LNs was assessed on days 7 or 8 (a) and after 5 wk (b). Lines connect data from individual mice, and plots summarize data pooled from three experiments. Analysis was performed using an unpaired two-tailed Student’s t test. ***, P < 0.001.