Perturbations in Peyer’s Patch B Cell Populations Indicative of Priming for a Secretory IgA Response

Many years after Johann Peyer described localized accumulations of lymphoid cells in the mammalian intestinal mucosa (Peyer’s patches, PP) (1) we proposed a special role for them in the development of secretory IgA responses (2). Initially we found that rabbit PP cells were enriched sources of precursors for IgA-plasma cells and could repopulate the spleen and intestinal lamina propria of irradiated recipients with such plasma cells much more effectively than could lymphoid cells from other sources (2). This was a somewhat accidental finding made while trying to elucidate the mechanism for transporting IgA from lamina propria plasma cells into the gut lumen. Jose O’Daly had been following up the detection of secretory component (SC) in glandular epithelial cells (3) and observed that many of the apparently nonspecialized epithelial cells lining the Lieberkuhn crypts contained numerous cytoplasmic granules that stained positively for both IgA and SC (4). The issue became the direction of flow — were the granules the result of endocytosis of sIgA from the intestinal fluid in the crypt lumen or were they formed at the plasma membrane on the basal side of the cells from IgA dimer secreted by the proximal plasma cells?