Abstract
The Peyer's patches of the terminal ileum are a source of IgA plasma cells in the intestinal lamina propria of experimental animals. They are also thought to harbour IgA memory cells. However, the microanatomical location of Peyer's patch memory cells, and whether they are also present in man is not known. Human Peyer's patches have a pronounced marginal zone (MGZ) of sIgD-negative B cells. In this study we analysed the sequence of polymerase chain reaction-amplified, rearranged IgVH genes from microdissected MGZ B cells, to determine whether this is a site of B-cell memory in Peyer's patches. We observed that the majority of Peyer's patch MGZ B cells contain heavily mutated IgVH genes and are therefore clearly memory B cells. Sequences of rearranged mutated genes in the MGZ have a pattern of replacement and silent mutations expected of selected products of the affinity maturation process. Related clones, with identical CDR3 but different patterns of mutation, are seen. This suggests that either these memory cells are formed as the germinal centre selection process proceeds, or a memory cell has re-entered the germinal centre for further rounds of mutation. Interestingly, in one patient, the MGZ in the Peyer's patches also contains a proportion of B cells with unmutated IgVH 4.21 genes.