A New Approach for Identification of Rat Lymphatic Capillaries Using a Monoclonal Antibody

In order to discriminate rat lymphatics from blood vessels on tissue cryosections by immunohistochemistry, a mouse monoclonal antibody (B27) was produced by immunization of mice with a homogenate of rat thoracic duct. B27 strongly recognized endothelial cells of almost all rat lymphatics, such as lacteals, lymphatic capillaries in the diaphragm at sites of absorption from the peritoneal cavity, collecting lymphatics and the thoracic duct. Besides the lymphatics, B27 reacted with the endothelium of some types of blood vessel, the mesothelium of the peritoneal cavity and substances between smooth muscle fibers. A new double immunostaining technique was then developed to distinguish the lymphatic capillaries, having no or only scanty basement membranes more clearly from the blood vessels. Cryosections were stained first with an anti-type IV collagen antibody for basement membranes, secondly with B27 for the endothelium, and then examined by either light microscopy or fluorescence microscopy. With this technique, the lymphatic capillaries were easily distinguished from other vessels by their positive reaction with B27 alone. B27 appears to be very useful for the simple and reliable identification of rat lymphatics, particularly lymphatic capillaries, in various tissues when applied for double immunostaining.