Normal B-cell population sizes in the absence of β1 and β7 integrins. (A) Representative histogram overlays show the β1 integrin expression on immature (B220med) and mature (B220hi) B cells of BM and spleen, respectively, of control (filled) and β1β7 mutant BM chimeras (line). (B) Single-cell suspensions from spleen of control and β1β7 mutant BM chimeras 6 months after polyIC treatment were prepared, stained with B220-FITC antibody, and subsequently sorted using anti-FITC MACS beads. Left panel: FACS analysis of the B220⁺-enriched fraction indicated higher than 95% purity (representative histogram is shown). Right panel: DNA was prepared from MACS-enriched B220⁺ splenocytes, analyzed by Southern blot, and densitometrically evaluated. The bar graph shows the relative amount of B220⁺ cells deficient for a functional β1 integrin gene. Error bar shows the standard deviation (n [control BM chimera]/[β1β7 mutant BM chimera]: 5/5).