Study of intestinal cell differentiation with monoclonal antibodies to intestinal cell surface components

Monoclonal antibodies that react with antigens of the plasma membrane of rat intestinal villus and crypt cells have been prepared by fusion of mouse myeloma (NSI) cells with spleen cells of mice immunized with various intestinal cellular fractions, including the luminal membrane of adult villus and crypt cells, and of newborn rat intestinal cells. The antigenic targets of most antibodies have been identified. They include major protein components of the brush border (luminal) membrane of adult villus cells (sucrase-isomaltase, maltase, lactase, aminopeptidase N, alkaline phosphatase) and newly identified protein antigens specific for intestinal epithelial cells. Of 25 independently derived monoclonal antibodies prepared, 18 reacted exclusively with the brush border membrane of the villus cells, confirming its unique protein composition. Antibodies specifically staining the crypt cells, the newly differentiated epithelial cells present in the lower half of the villi, the top villus cells, and both villus and crypt cells were also obtained and characterized. These antibodies have been used to study the expression of cell- and tissue-specific functions during differentiation and development of the intestinal epithelium. Contrary to results obtained with polyclonal antisera, no inactive forms of the brush border enzymes have been detected in the crypt cells. The identification of cell surface components expressed at different levels of the villi, and in both undifferentiated and differentiated intestinal cells, suggests that cell differentiation in the intestinal epithelium is a continuous and gradual process involving both transcriptional and translational regulation of different sets of genes.