Individual centroblasts vary widely in their surface MHCII levels. (a) C57BL/6 mice were immunized with SRBCs by i.p. injection and GC B cells were gated using an IgD^low CD95^high GL7⁺ gating scheme. GC B cells were subgated into four populations based on their surface MHCII (I-A^b) and CXCR4 levels. (b) Back gating on populations A–D confirmed that the CXCR4^high MHCII^low population displays staining patterns of GC B cells. Horizontal lines indicate means. (c) Populations A–D were FACS sorted and subjected to RT-PCR. Data were normalized to Hprt. (d) CD86 and CD83 surface staining was compared for the four GC subsets, color coded as in a. Points in c represent individual samples from separate mice, with data pooled from two experiments. Data in a, b, and d are representative of four mice analyzed in two experiments.