Monoclonal antibodies were produced by immunizing BALB/c mice with freshly prepared canine thymocytes and peripheral blood leukocytes. Flow cytometric analysis of canine peripheral blood leukocytes showed that an antibody, designated 169.1, recognized about 60% of non-lymphoid cells, but reacted with less than 3% of lymphocytes. Immunohistochemistry using frozen sections showed that several types of epithelial cells such as epithelial reticulum cells in the thymus and ductal system in the parotid gland exhibited an intense positive reaction to antibody 169.1. Moreover, the ellipsoidal sheath in the spleen and non-myelinated nerve fibers in the peripheral nervous system had selectively positive reactions ; in the latter, filamentous structures were visible under a light microscope. In contrast to the data from the flow cytometric analysis, no leukocytes on sections reacted with 169.1. Immunoblot assay revealed that 169.1 recognized antigens with molecular weights of 48 and 52 kDa under reducing conditions. These findings characterize 169.1 as an antibody against a cytoskeletal protein rich in epithelial cells and neurons
