Veiled cells in the gastrointestinal tract.

: Lately it has become known that for the initiation of an immune response an antigen presenting cell is needed. In the skin the antigen presenting cell system has been studied and is extensively supposed to consist of Langerhans' cells in the epidermis and dermis, veiled cells in the skin lymph, and interdigitating cells in the skin lymph nodes. These cells are considered to belong to the mononuclear phagocyte system which is in principle composed of cells stemming from the promonocyte/monocyte. To detect whether an antigen presenting cell system is present in the gut, we studied cell suspensions of gut tissues. Monoclonal cells with long actively moving cytoplasmic veils were found in cell suspensions from small intestinal villi of guinea pig and pig, but not of rat. These veiled cells appeared to be strongly Ia positive, as are the cells from the skin antigen presenting system. They share several ultrastructural and enzyme cytochemical characteristics with these skin cells. Gut veiled cells localize within the lympho-epithelium of Peyer's patches of the rat, just underneath this lympho-epithelium and in the T-dependent interfollicular area, according to Ia stainings on frozen tissue sections and to ultrastructural observations. From stainings with anti-IgA, -IgE, -IgG, -IgM and anti-T lymphocyte sera it is concluded that these cells do not belong to the lymphocyte series. It is suggested that these gut veiled cells belong to the monocyte/macrophage family and form an antigen presenting cell system in mucosa-associated lymphoid tissue, similar to the antigen presenting cell system in the skin.