Production of a monoclonal antibody strongly reacting with immature thymic T lymphocytes and its immunohistological application.

A monoclonal antibody Th-5 has been produced against mouse immature thymic lymphocytes and employed to study the process of T cell differentiation in the thymus. Immunohistologically, Th-5 positive thymic T lymphocytes were first found at Day 12 of gestation. They increased in number as well as staining intensity until Day 18 of gestation and decreased thereafter. Th-5 antigen expression was not seen in lymphoid cells in the fetal liver. In the newborn thymus, lymphocytes in the subcapsular layer were still strongly positive, while other cortical lymphocytes became moderately positive for Th-5. Th-5 positiveness was more pronounced in the medulla than in the cortex in the thymus of young adult mice. The staining pattern of Th-5 in the thymus was apparently different from those with other T cell markers (Thy-1, CD3, CD4, CD5, CD8) including J11d, Pgp-1, IL-2R, and 3A10 (TCR gamma delta). Flow cytometric analyses showed that the expression of Th-5 was mostly associated with the Thy-1 antigen. However, the fluorescent intensity of Th-5 gradually declined with ontogenic development of the thymus, and the molecular size of the antigen was approximately 100 kDa, which is different from Thy-1 antigen (25-30 kDa). Considering these findings, the strong expression of Th-5 could be one of the markers of immature thymic T lymphocytes in the early phase of the ontogenic development.

Age-related hyperplasia of the thymus and T-cell system in the Buffalo rat. Immunological and immunohistological studies.

This report describes the development of hyperplasia of both the thymus and the peripheral T-cell system with advancing age in the Buffalo rat. Buffalo/Mna rats do not show age-related thymic involution, but rather develop thymic hyperplasia with advancing age. This thymic growth is expansile and there is no infiltration of the surrounding tissues. Because the enlarging thymus occupies the thoracic cavity, most of the rats die of respiratory failure by the age of 24 months. Thymic enlargement is due to primary hyperplasia of cortical epithelial cells and the large number of proliferating lymphocytes. The hyperplastic epithelial cells are bizarre in shape and strongly positive when stained with Th-3 monoclonal antibody (MoAb), anti-thymosin antibody and anti-EGF antibody, but negative with Th-4 MoAb. The patterns of distribution of CD-5+, CD-4+ and CD-8+ lymphocytes within the hyperplastic thymus are similar to those seen in young rats of other species. The high level of T-cell emigration from the thymus to the periphery appears to persist throughout life, since the percentage of normal splenic T-cells also increase with advancing age and exceed 70% of the total by 24 months of age. This thymic enlargement with abnormal hyperplasia of cortical epithelial cells can be prevented by hypophysectomy.

Immunohistochemical studies in human thymomas. Localization of thymosin and various cell marker.

Forty five human thymomas were studied immunohistochemically using antibodies to thymosin x-1, thymosin beta-3, cortical epithelium of human thymus (UH-1), mouse thymic nurse cells (Th-3) and Leu-7. Most thymomas were found to contain thymosin x-1 (80%) and thymosin beta-3 (89%). Also used in the study were a new monoclonal antibody (UH-1), which reacts with the epithelial cells forming a meshwork in the cortex of the normal newborn thymus and Leu 7, which reacts with subcapsular epithelial cells in the outer thymic cortex. The combined use of UH-1 and Leu-7 was found to identify neoplastic epithelial cells of thymic cortical origin in thymomas. Approximately 80% (37/45) of the thymomas in the present study reacted with Leu-7, UH-1 or both antibodies, and were thus considered to be derived from cortical thymic epithelium. Of the eight thymomas which were negative with both Leu-7 and UH-1, four were histologically of mixed type characterized by the formation of epithelial cell islands. All four of these thymomas were positive with thymosin and were therefore considered to be of medullary origin. Ten of the thymoma were associated with myasthenia gravis; all were positive with UH-1 and were consider to be of cortical origin.

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.