Analysis of the thymic microenvironment by monoclonal antibodies with special reference to thymic nurse cells.

Two hybridoma cell lines secreting monoclonal antibodies against stromal tissues of mouse thymus were produced using the spleen cells of BALB/C mice immunized with newborn thymic homogenate of C57BL/6 mice emulsified in Freund's complete adjuvant. The monoclonal antibody Th-3 reacted with stromal cells in the thymic cortex and the monoclonal antibody Th-4 reacted with stromal cells in the thymic medulla. The stromal cells revealed by Th-3 showed a meshwork structure in the cortex, and formed a monolayered border at the cortical surface and around the vasculature. Each mesh of this structure was connected to each other, forming a complex labyrinth and being open toward the medullary area. Neither lymphoid cells nor any cells in any other organs were reacted with this Th-3 antibody. However, the reactivity of Th-3 with the thymic cortical stromal cells was observed not only in C57BL/6 mice which had been used as source of antigen, but also in other strains of mice such as C3H and BALB/C. Immunoelectron microscopy revealed that Th-3 monoclonal antibody was reactive with some component, diffusely present in the cytoplasm of cortical epithelial cells. The pattern of Th-3 positive meshwork in the thymic cortex was quite similar to that stained by either anti-IA or anti-IE antibody, but the Th-3 positive reaction was not inhibited by these anti-IA and anti-IE antibodies. Thymic nurse cells prepared by the method of Wekerle were positive for Th-3 antibody. On the contrary, Th-4 reacted only with epithelial cells in the thymic medulla. It was suggested that Th-3 monoclonal antibody detected some antigen specific to so called thymic nurse cells.