Identification of a novel antigen on the apical surface of rat alveolar epithelial type II and Clara cells

Here we describe a monoclonal antibody (MMC4) that recognizes a novel antig en on the apical surface of rat alveolar epithelial type II and Clara cells in the lung, proximal tubule epithelial cells in the kidney, and villus ep ithelial cells in the small intestine. Biochemical analysis showed that the MMC4 antigen was sensitive to heating and proteinase K digestion and that it is distributed in the detergent-rich phase after Triton X-114 phase sepa ration. These data suggest that the MMC4 antigen is an integral membrane pr otein. Glycerol gradient sedimentation identified two forms of the MMC4 ant igen: one with a sedimentation coefficient of 10.1 and one with a sedimenta tion coefficient of 1.66, suggesting that the antigen may be part of a mult iprotein complex. During rat development (fetal day 16 to adult), the MMC4 antigen increased 12-fold in the lung and 200-fold in the kidney. In the in testine, the MMC4 antigen increased 150-fold by neonatal day 1 and then dec reased to adult values. Our data demonstrate that the MMC4 antigen is unlik e known type II cell- and Clara cell- associated proteins. The MMC4 monoclo nal antibody will be useful as a marker of epithelial cell phenotype in dev elopment and injury studies.