The B-B7h transgene is overexpressed on activated and plasma B cells in the presence of endogenous B7h. (A) Purified B cells from B7h+/−, B7h−/−, and B-B7hTg mice on the B7h+/− and B7h−/− backgrounds were cultured for 72 hours in the presence of activating stimuli, and cell surface B7h levels were measured by FACS. Dashed lines represent staining of B7h on B7h−/− cells cultured in the presence of stimuli; solid lines represent cells cultured without stimuli, and shaded histograms represent cells cultured with stimuli, from mice of the genotypes shown on the right. (B) Seven days after immunization with NP-CGG, splenocytes from mice with the genotypes indicated in the legend were analyzed by FACS for cell-surface B7h levels and lineage markers. Naïve B cells were gated B220+IgD+, germinal center B cells were gated B220+IgDnegGL7+CD95+, and plasma cells were gated IgDnegB220loCD138+.