MHCII^low GC B cells degrade their MHCII molecules more rapidly. (a) A fusion construct encoding the photoconvertible protein mKiKGR fused to the intracellular tail of the I-A^b β chain was generated. Exposure of the encoded protein to violet light causes a permanent switch between green and red states. BM cells were transduced with the construct and used to reconstitute lethally irradiated recipients. (b) Reconstituted mice were immunized with NP-CGG/alum and iLNs photoconverted 8–9 d later. iLNs were harvested without conversion or at various time points after photoconversion, and transduced (Thy1.1⁺) GC B cells were interrogated for their expression of endogenous surface MHCII and I-A^bmKiKGR^red. (c) Cells were gated according to high and low levels of endogenous MHCII (dashed lines in b), and the relative difference in I-A^bmKiKGR^red signal in the MHCII^low versus MHCII^high cells is plotted for multiple mice from three experiments (two to six mice per experiment), with each symbol representing individual animals. Horizontal lines indicate means. Analysis was performed using an unpaired two-tailed Student’s t test. ***, P < 0.001.