Immunocytochemical identification and localization of immunoglobulin A within Paneth cells of the rat small intestine.

Light microscopic immunocytochemistry was used to identify Paneth cells by their lysozyme content and to detect immunoglobulin antigens within a subpopulation of these cells. Antisera specific for the heavy chains of rat or human immunoglobulin A and for immunoglobulin light chain antigens produced specific staining of rat Paneth cells. The distribution of immunoglobulin staining varied between adjacent Paneth cells in the same crypt and between Paneth cells in adjacent crypts, as well as between Paneth cell populations of different animals. No staining of rat Paneth cells was detected using antisera specific for the heavy chain of immunoglobulins G or M. The specific staining of Paneth cells for immunoglobulin A and light chain antigens was blocked by absorption of each antiserum with its respective purified antigen. Absorption of these antisera with purified rat lysozyme did not affect staining and thereby eliminated the possibility of immunologic cross-reactivity between lysozyme and immunoglobulin antigens. It is suggested, in light of current concepts of Paneth cell function, that the immunoglobulin staining of Paneth cells may reflect their ability to phagocytize immunoglobulin A-coated microorganisms or immune complexes containing immunoglobulin A.