The phenotype of lymphocytes in a thymoma as studied with monoclonal antibodies

Thymoma mimicking lymphoblastic lymphoma: a pitfall in fine-needle aspiration biopsy interpretation

Lymphocyte-rich thymoma often contains lymphoblasts and lymphoblastic lymphoma often infiltrates the thymus gland. Although these two neoplasms are clinically distinct in most case, their cytologic features may be similar on biopsy. We describe a fine-needle aspiration biopsy of a thymoma in a 50-yr-old man to increase awareness of this pitfall in cytologic interpretation.

Immunophenotype of thymoma-associated lymphoid cell component of T-cell type. A new analytic procedure in keeping with structural heterogeneities

The phenotype of the lymphoid cell component of 35 thymomas was investigated by analyzing cryostat sections and lymphocyte suspensions. The morphology in each case was determined by examining multiple tissue samples from different parts of the tumor. Structural heterogeneity was shown in 14 thymomas, and a homogeneous morphology of cortical or medullary or mixed types in the others. To assess whether this heterogeneity was correlated with differences in the lymphoid phenotype, we analyzed both lymphocyte suspensions and frozen sections from the same samples. Phenotypical differences in the suspensions of each thymoma in the heterogeneous group were noted and similar differences were also observed in the cryostat sections. Phenotypical abnormalities were found in some thymomas. They consisted of the simultaneous expression of cortical and medullary markers, which was most marked in the heterogenous mixed-type thymomas invading the lung. Furthermore, the global phenotype was tested on a pool of lymphocyte suspensions in all thymomas. This procedure distinguished cortical, medullary and intermediate cortico-medullary immunophenotype models which closely correlated with the tumor histology. It was concluded that, due to the frequent structural and immunological heterogeneity of thymomas, correct assessment of their lymphoid component requires a two-step analysis. This comprises: 1) individual suspensions from samples taken from different areas of the same thymoma, and 2) a pool of these suspensions. The first step will reveal the different immunological characteristics. In the second, the lymphocyte phenotype, which may vary widely throughout the tumor, will be represented in its totality. These findings may be of great help in predicting clinical patterns, especially possible malignant evolution.

Studies on lymphocyte subsets in thymic tissue and functions of peripheral lymphocytes in patients with tumorous thymus with special reference to myasthenia gravis

In order to obtain a better understanding of the immunological abnormalities present in myasthenia gravis (MG), which is often accompanied by thymoma or thymic hyperplasia, we investigated lymphocyte subsets and their functions using samples of thymoma or thymic hyperplasia tissues from 11 patients (6 cases with MG), and peripheral blood from 6 patients (4 cases with MG). In most thymic tissues from patients with MG, a maturating tendency of lymphocytes was generally observed. Especially in the medulla of thymic hyperplasia, an entirely peripheral blood type of T-lymphocytes, which were Leu-6- and either Leu-2a+ or 3a + 3b+, were encountered abundantly. Therefore, the presence of abnormal maturation of lymphocytes in the thymus or destruction of the barrier between the thymus and the peripheral blood in MG cases was indicated. In cases without MG, no such tendency was noted. As to the peripheral blood in patients with MG, concanavalin A-induced suppressor cells were significantly decreased (p less than 0.01). All of these changes were considered to be intimately related to the appearance of MG.

Immunoglobulin and T-cell receptor genes in thymomas: genotypic evidence supporting the nonneoplastic nature of the lymphocytic component

On the basis of morphologic and immunophenotypic studies, it is generally accepted that the lymphocyte population in thymomas is not neoplastic. We studied 10 thymomas with restriction endonuclease and Southern blot/DNA hybridization methods in an attempt to provide genotypic evidence in support of this hypothesis. The clinical, gross, and microscopic features of each case were reviewed and found to be entirely consistent with the diagnosis of thymoma. In addition to conventional histologic methods, we also studied each tumor by immunohistologic techniques. The lymphocytes generally had an immunotype characteristic of immature cortical thymocytes, and the epithelial cells were uniformly stained by antikeratin antibodies. DNA probes for the T-cell receptor beta-chain gene and immunoglobulin genes (C kappa, C lambda, and JH) were used in the genotypic studies. No gene rearrangements were detected in any of the thymomas. This study provides additional evidence that clonal proliferations of T or B lymphocytes are not present in thymomas; therefore, these cells are almost certainly not neoplastic. The results also provide a basis for the effective use of restriction endonuclease and Southern blot/DNA hybridization analysis in the differential diagnosis of non-Hodgkin's lymphoma and thymoma.

Lymphocyte subsets in human thymoma studied with monoclonal antibodies

Lymphocyte subsets were investigated using OKT series monoclonal antibodies and flowcytometry in 16 cases of thymoma. From the viewpoint of lymphocyte subsets, thymoma could be divided into three types: thymus lymphocyte type, peripheral lymphocyte type, and intermediate type. In thymus lymphocyte type, the number of OKT-6+ cells exceed that of OKT-3+ cells, and are more than 50%. In peripheral lymphocyte type, the number of OKT-6+ cells are less than that of OKT-3+ cells and less than 10%. In intermediate type, OKT-6+ cells are between 10% and 30%. These three types correlate well with the histologic features with respect to the number and distribution of lymphocytes in thymoma tissue. Lymphocytes were infiltrating abundantly and intermingled in the tumor cell nests in thymus lymphocyte type, and were infiltrating rather scantly and outside the nests in peripheral lymphocyte type.

Fc gamma receptors and HLA-DR antigens on thymus cells in myasthenia gravis

Receptors for the Fc part of IgG (Fc gamma R) and HLA-DR antigens were detected in thymus tissue from patients with myasthenia gravis (MG) using monoclonal antibodies (B1D6 and OKIa1) in indirect immunofluorescence. The amount of Fc gamma R and HLA-DR antigens was increased on epithelial reticular cells and on interdigitating reticular cells in hyperplastic thymus as compared to normal thymus. In thymomas from MG patients the neoplastic epithelial cells expressed Fc gamma R, whereas only a few cells had HLA-DR antigens. Neither thymocytes nor B lymphocytes in the hyperplastic thymuses and in the thymomas were stained by B1D6.

Immunohistological evidences of cortical and medullary differentiation in thymoma

The phenotypical characteristics of human epithelial and lymphoid cells have been studied with immunohistochemical methods on frozen sections of 12 thymomas. On the basis of the cytohistological characteristics of thymoma epithelial cells (EC) the thymomas were divided in cortical, medullary and mixed types, according to recently developed light microscopical criteria. When tested with a series of monoclonal antibodies, thymoma EC were all stained by the antibody Ki-M3 (as in the thymus), but reacted with anti-HLA-DR, anti-HLA-A,B,C and with a new monoclonal antibody to cortical EC, 21A6, to a lesser extent and with weaker, variable intensity in comparison with the normal thymus. Cortical type thymomas were most reactive and the medullary type almost negative. Thymomas, like normal thymus showed different immunoreactivity patterns with antibodies to prekeratins of different specificities. Cortical type thymomas and areas in mixed thymoma showed an EC staining with the antibody to non-squamous type keratin (35 beta H11) whereas medullary type thymomas and areas showed staining with antibodies to squamous-type keratin (34 beta E12-IV/82) in addition. Lymphoid cells with cortical (OKT6+, Leu 1 weakly+, Leu 2a+, Leu 3a+) or mature medullary (OKT6-, Leu 1 strongly+, Leu 2a or Leu 3a+) phenotype were found to colonize tumours with different EC types. These immunohistochemical findings largely confirm our earlier cytological distinction of thymoma EC. In addition important differences have been observed in neoplastic cortical EC concerning the HLA-DR and 21A6 immunoreactivity that may be intimately related to the neoplastic process and paraneoplastic immune phenomena.