POTASSIUM-DEPENDENT PARA-NITROPHENYL PHOSPHATASE AND CARBONIC-ANHYDRASE REACTIVITIES SUGGEST THAT LYMPHOID FOLLICLES IN THE LARGE-INTESTINEOF LAMBS ARE LINED WITH A UNIFORM TYPE OF EPITHELIAL-CELL DISTINCT FROM THE ABSORPTIVE EPITHELIUM

The epithelium covering the large intestinal lymphoid follicles in fet al and postnatal lambs was examined for potassium-dependent p-nitrophe nyl-phosphatase (K+-NPPase), carbonic anhydrase, magnesium-dependent a denosine triphosphatase (Mg2+-ATPase) and acid phosphatase. Reactiviti es for these enzymes indicated a homogenous population of cells in the follicle-associated epithelium (FAE), distinct from the absorptive ep ithelium. There were essentially no differences in the enzyme reactivi ties of the large intestinal FAE between fetuses in late gestation and postnatal lambs. The FAE showed a weak reaction for K+-NPPase and a v ariable staining for Mg2+-ATPase and acid phosphatase. In contrast, th e adjacent absorptive epithelium demonstrated strong reactions for the se enzymes. Carbonic anhydrase gave a strong reaction at the luminal a nd apparent basolateral cell borders of the large intestinal FAE. This distribution of reactivity for carbonic anhydrase resembled that foun d in the ileal FAE. In absorptive epithelial cells, only the luminal c ell border reacted strongly for carbonic anhydrase. Serial sections of large intestinal tissue showed a variation in the basolateral stainin g of FAE from one section to the next, a finding which suggested that the reaction may be associated with transcytosis. The lymphoid follicl es and domes of the large intestine showed a variable granular pattern of carbonic anhydrase staining, which also suggested a dependence on epithelial transcytosis.