The gut-associated lymphoid system: nature and properties of the large dividing cells

Cellular kinetics of the intestinal immune response to cholera toxoid in rats

The aims of this study were (a) to find a regime of immunization with cholera toxoid in rats which would establish a high density of antitoxin containing cells (ACC) in the lamina propria of the intestine and (b) to determine the origin of the ACC. The best cellular response was achieved by a single i.p. dose of toxoid in FCA followed by an intraintestinal boost 2 wk later. ACC appeared in the thoracic duct lymph 2 days after boosting, reaching a peak of about 200,000 ACC/h at 3--4 days. This was followed by the appearance of large numbers of ACC in the intestine. The i.p. dose of toxoid by itself gave rise to very few ACC in the gut or thoracic duct lymph, but it had clearly primed the gut immune system for a secondary response. Priming was also achieved by the prolonged oral intake of toxoid. The importance of the intestinal route for boosting was shown by the failure of i.p. challenge to give an ACC response in the intestine after i.p. priming and the small response it provoked after oral priming. ACC among thoracic duct lymphocytes (TDL) and in the lamina propria contained predominantly IgA. Two observations indicated that the major source of the lamina propria ACC was from cells that emerged in the thoracic duct lymph after intraintestinal challenge. Firstly, the establishment of a thoracic duct fistula immediately before challenge prevented the appearance of ACC in the intestine. Secondly, many ACC appeared in the intestine of normal rats after the injection of TDL rich in ACC. Although homing of ACC precursors to the gut was not antigen-dependent, the distribution of ACC in the lamina propria was considerably influenced by the site of the intestinal challenge, the density of ACC being greatest at or distal to the site of injection of toxoid into the lumen of the gut.

Studies of intestinal lymphoid tissue. I. Electron microscopic evidence of 'blast transformation' in epithelial lymphocytes of mouse small intestinal mucosa

The morphology of epithelial lymphocytes in osmium-fixed, Epon-embedded jejunum of adult mice was studied by light and electron microscopy. Toluidine blue-stained 1 mum 'thick' plastic sections were compared with adjacent thin sections, thereby permitting precise ultrastructural identification and description of selected epithelial lymphocytes. Their size and appearances varied considerably, ranging from typical small lymphocytes through medium-sized lymphocytes to large immunoblasts. A high proportion of medium-sized epithelial lymphocytes (mean diameter 6-9 +/- 1-1 mum) contained several lysosomes, extensive Golgi complexes, prominent centrioles and abundant ribosomes. Their appearances, therefore, corresponded directly to mitogen-stimulated lymphocytes. In contrast, immunoblasts were big cells (mean diameter 11-0 +/- 0-8 mum) with large, euchromatic nuclei and prominent nucleoli. The majority had pale-staining, ribosome-studded cytoplasm and thus resembled type I, or T blasts. Very rarely, densely staining blasts containing ribosomes and well developed rough endoplasmic reticulum were observed; these corresponded to type II or B blasts. These observations indicate that transformation of lymphocytes occurs within the interepithelial cell spaces of the small intestinal mucosa, suggesting that epithelial lymphocytes are immunocompetent cells which may be responsive to local antigenic stimulation.