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The synthesis of secretory component by the human thymus.


 The existence in human external secretions of an additional component, originally called secretory “piece” and attached to the majority of IgA molecules is now well established (1). Secretory “piece” (now called secretory component or S component) has been isolated from the intact secretory IgA molecule and from the secretions of normals and patients with agammaglobulinemia in which it occurs “free” or unassociated with IgA. An apparently analogous component has been identified in several animal species, particularly the rabbit (2) and cow (3). In each of these species, S component has been shown to be a glycoprotein with a m.w. of approximately 60,000. S component has been shown to be synthesized in a variety of epithelial cells including those of the GI and respiratory tracts, kidney, sweat glands, pancreas and gallbladder (4). We here describe the synthesis of S component in the human thymus and its immunohistologic localization in Hassall's corpuscles and in the epithelial cells surrounding these structures.