Germinal center B cells in Peyer's patches of aged mice exhibit a normal activation phenotype and highly mutated IgM genes.
Rogerson BJ, Harris DP, Swain SL, Burgess DO. Germinal center B cells in Peyer's patches of aged mice exhibit a normal activation phenotype and highly mutated IgM genes. Mech Ageing Dev. 2003 Feb; 124(2):155-65.