Simultaneous demonstration of two antigens on single T cells using antibodies with contrasting labels

We describe a double labeling method for the discrimination of 2 antigens on single cells. It consists of a combination of 3H-immunoautoradiography and immunocytochemistry applied to cells previously fixed on poly-L-lysine (PLL)-coated multispot slides. The method has been applied to various mouse cells contemporaneously labeled with 2 different monoclonal antibodies. In order to distinguish the attached antibodies unambiguously, they were labeled with contrasting markers. One of the antibodies was marked with tritium blackening the photographic film that covers the slide. The other was detected with the peroxidase-anti-peroxidase (PAP) method forming a reddish precipitate. The contrast between the reddish reaction product of the PAP-labeled antibody and the black silver grains allows cells, specifically labeled with both antibodies, to be distinguished from cells labeled with only one or neither of the antibodies. Tritium-labeled antibodies were introduced because of their advantage over antibodies labeled with iodine in the closer localization of the silver grains to the bound antibody and their much longer halflife (60 days versus 12 years). In this study we applied a tritium-labeled anti-Thy-1.1 together with anti-Lyt-1 monoclonal antibody for studying the distribution of the corresponding antigens on lymphocytes in the mouse thymus and lymph node cells.