Large mononuclear Ia-positive veiled cells in Peyer's patches. II. Localization in rat Peyer's patches.

Dendritic Ia-positive veiled cells were seen in frozen sections of rat Peyer's patches within the lymphoepithelium, in the reticular area just underneath and in the T-dependent interfollicular area. From immunohistochemical stainings with anti-IgA, IgE, IgG, IgM and monoclonal anti T lymphocyte sera it is concluded that these Ia-positive cells do not belong to lymphocyte series. The ultrastructure of these Ia-positive veiled cells resembled the morphology of the veiled cells found in Peyer's patch cell suspensions and in skin lymph. It is suggested that these cells form an antigen presenting cell system in mucosa-associated lymphoid tissue, similar to the antigen presenting cell system in the skin.