In germinal centers, somatic hypermutation and secondary BCR rearrangement are involved in BCR affinity maturation. The modified BCRs with lower affinity will be removed by apoptosis. Tingible body macrophages are responsible for the MFG-E8-dependent clearance of apoptotic cells. Tingible body Mφs in wild type mice engulfed and digested the apoptotic B cells efficiently, whereas the MFG-E8(-/-) Mφs just wrapped many apoptotic cells without engulfment42. The MFG-E8(-/-) mice developed splenomegaly in an age-dependent manner. The white pulps in the spleens of the MFG-E8(-/-) mice were greatly enlarged and carried numerous germinal centers.