BRUSH-BORDER MEMBRANE ALKALINE-PHOSPHATASE ACTIVITY IN MOUSE PEYERS PATCH FOLLICLE-ASSOCIATED ENTEROCYTES

1. Using a new method of quantitative cytochemistry to determine alkaline phosphatase activity, it was possible to identify M cells and distinguish two further types of enterocytes present in mouse Peyer's patch follicle‐associated epithelial tissue. 2. A quantitative description of these three cell types was provided by making direct absorbance measurements of enzyme reaction product on the luminal surface of individual follicle‐associated enterocytes. M cells having a negligible alkaline phosphatase activity had a mean absorbance of 6 +/‐ 2 arbitrary units. The other two populations of enterocytes had overlapping but significantly different mean absorbances of 20 +/‐ 2 and 30 +/‐ 3 arbitrary units. 3. M cells accounted for 3.2 +/‐ 1% of the total number of cells present in the apical part of the follicle‐associated epithelium. This percentage is a minimum value describing an extreme example of cells having M cell‐like characteristics. The remaining epithelial cells were divided equally between those having high and low alkaline phosphatase activities in their brush‐border membranes. A small percentage of cells having low alkaline phosphatase activities could perform M cell functions. 4. Results obtained suggest that reduced alkaline phosphatase activity and brush‐border membrane Cl‐ conductance can both be used as differentiation markers to identify a large population of poorly differentiated enterocytes present in mouse follicle‐associated epithelial tissue. © 1990 The Physiological Society