Immunohistochemical observations of immunoglobulin A in the Paneth cells of germ-free and formerly-germ-free rats.

The localization of secretory immunoglobulin A (IgA) in Paneth cells was immunohistochemically studied in germ-free (Gf) and ex-Gf rats that had been injected with feces obtained from specific-pathogen-free (SPF) rats. In Gf as well as SPF rats, the secretory granules of Paneth cells and the brush borders of crypt cells exhibited IgA immunoreactivity. At 12 and 24 h after inoculation, it was found that, concomitant with the occurrence of considerable degranulation, the IgA immunoreactivity in Paneth cells disappeared, except of the margin of supranuclear vacuoles. In contrast, the IgA immunoreactivity of the crypt-cell brush borders was unchanged. Four days after inoculation, secretory granules exhibiting IgA immunoreactivity reaccumulated in Paneth cells. The present study suggests that Paneth cells regulate the bacterial milieu in the intestine by releasing secretory granules containing IgA into the crypt lumen.