Clonality of splenic tissue from EμCycD1CD19CREBimfl/flmice. Spleens from 2 exemplary EμCycD1CD19CREBimfl/fl mice, (A) 1 that developed MCL and (B) 1 that did not are compared for CD5 expression, CD23 expression, and (C) immunoglobulin H clonality by framework 3 PCR.