Human Thymoma Research Articles

Mapping of two genetic loci, Ten-1 and Ten-2, associated with thymus enlargement in BUF/Mna rats.

The thymoma-prone BUF/Mna rat is a useful model for human thymoma. Thymoma develops spontaneously in these rats at an incidence of nearly 100%. At pre-thymoma age, BUF/Mna rats have extremely large thymuses when compared with those of rats of the other strains, suggesting the presence of genes that regulate the thymus enlargement. We performed linkage study to identify the genetic loci associated with thymus enlargement in {(WKY/NCrj x BUF/Mna) F1 x BUF/Mna} backcross rats. Linkage study showed the significant associations between thymus size and markers on Chromosomes (Chrs) 1 and 13, suggesting the presence of two genes, Ten-1 and Ten-2, which regulate the thymus enlargement. Ten-1 was located between myosin light chain, muscle 2 (MYL2) and D1Mgh11 loci on Chr 1, and Ten-2 was located between synaptotagmin II (SYT2) and D13N2 loci on Chr 13.

Accumulation of Immature CD3 -CD4 +CD8 - Single-Positive Cells That Lack CD69 in Epithelial Cell Tumors of the Human Thymus

Human thymomas are epithelial tumors that are associated with a large number of nonneoplastic T cells of mainly immature phenotype, suggesting that epithelial cells of thymomas retain the function of thymic cortical epithelium. We report here that a large proportion (16-85%, mean ± SD 58 ± 22%, n = 17) of CD4 + single-positive T cells within the thymoma lack cell surface expression of CD3 and also of CD69, an early activation antigen that is expressed by positively selected thymocytes. Normal thymus had this CD4 +CD8 -CD3 - population at much lower levels (12 ± 7%, n = 11). It has been reported that in the human the CD4 +CD8 -CD3 - cells are the predominant population that is intermediate between the CD4 -CD8 - double-negative and CD4 +CD8 + double-positive stages. In contrast to CD4 + single-positive cells, most of the CD8 + single-positive cells in the thymoma as well as in the normal thymus expressed CD69 and a high level of CD3. A partial explanation of these observations is that the epithelial cells of thymoma were unable to positively select all the immature thymocytes generated in the thymoma. This relative inefficiency of positive selection could not be attributed solely to the paucity of MHC class II expression in the thymoma.

Immunoreactive thymosin α1 in human thymus and thymoma

Thymosin alpha 1-like immunoreactivity was assessed in human thymus and thymoma tissue extracts by means of a new radioimmunoassay that included an anti-thymosin alpha 1 mouse monoclonal antibody. Thymosin alpha 1-like immunoreactivity levels decreased with age in normal thymuses but not in thymomas. The average thymosin alpha 1-like immunoreactivity level was 45.0 +/- 52.1 ng/mg protein in normal thymuses and 273.9 +/- 205.0 ng/mg protein in thymomas. The average thymosin alpha 1-immunoreactivity level in thymomas was higher than that in normal thymuses. Thymosin alpha 1-like immunoreactivity levels in thymomas appeared to have no relationship to the clinical stage of the thymoma or associated diseases. When viewed according to histologic characteristics, the average thymosin alpha 1-like immunoreactivity level in polygonal cell thymomas (382.5 +/- 192.6 ng/mg protein) was significantly higher than that in the spindle cell thymoma (101.8 +/- 81.2 ng/mg protein). When viewed according to the degree of lymphocyte infiltration, thymomas could be classified according to four grades: absent, scant, moderate, and predominant. In predominant or moderate thymomas, the average thymosin alpha 1-like immunoreactivity level was higher than that in scant or absent thymomas. Also, thymosin alpha 1-like immunoreactivity levels in thymuses of patients with myasthenia gravis were relatively higher than those in patients with normal thymuses.

Chromosomal Mapping of Genetic Locus Associated with Thymus‐size Enlargement in BUF/Mna Rats

The thymoma‐prone rat of the BUF/Mna strain is a useful model for human thymoma. In this strain thymoma development is regulated by a single autosomal susceptible gene, Tsr‐1. At pre‐thymoma age, BUF/Mna rats have extremely large thyrauses, when compared to those of other strains of rats. Genetic studies in crosses between BUF/Mna rats with large thymuses and WKY/NCrj rats with small thymuses suggested the presence of a major autosomal gene, Ten‐1, which contributes to thymus enlargement in a backcross population. Linkage studies between Ten‐1 and microsatellite markers in backcross rats of (WKY/NCrj×BUF/Mna)Fl×BUF/Mna have led to the localization of Ten‐1 in chromosome 1. This result may provide an approach to clone Tsr‐1, which could be allelic to Ten‐1.

Expression of epidermal and nerve growth factor receptors in human thymus and thymomas.

The expression of epidermal growth factor (EGF) and nerve growth factor (NGF) receptors has been investigated by immunohistochemical analysis in eight normal human thymuses and in 15 thymomas. Thymomas were classified into five different histological types--medullary, mixed, predominantly cortical, cortical thymoma and well-differentiated thymic carcinoma. In fetal and paediatric normal thymus, EGF-receptor was expressed by subcapsular, cortical and medullary epithelial cells, whereas immunoreactivity for NGF-receptor was detected on only subcapsular and medullary epithelial cells. In thymomas, independent of their histological type, EGF-receptor was expressed by a large majority of epithelial cells. In contrast, the pattern of expression of NGF-receptor in thymomas was different for the various histological types. These findings indicate that the expression of both EGF and NGF receptors in human thymomas substantially reflects their expression in normal thymus, and suggest that EGF and NGF may play a role in the ontogenesis of the human thymus as well as in the histogenesis of thymomas.

Neoplastic epithelial cells in a subset of human thymomas express the B cell-associated CD20 antigen.

A series of 36 human thymomas have been immunohistochemically analyzed using a panel of antibodies recognizing B-cell markers including CD20. Most thymomas exhibiting the cortical pattern, according to the criteria of Marino and Muller-Hermelink, were characterized by areas of medullary differentiation containing variable numbers of CD20+ B lymphocytes, thus mimicking the medulla of normal thymus. On the other hand, B cells were absent or rare in thymomas recognized as mixed using the same morphological criteria. Surprisingly, we observed in most mixed thymomas variable numbers of CD20+ spindle cells, characterized by long slender processes. Using double-marker analysis we could demonstrate the epithelial nature of these cells (expression of keratin and lack of lymphoid and B-cell-related markers). The immunoreactivity of thymoma epithelial cells with L26, an antibody widely used in the characterization of B-cell lymphomas, can represent a drawback of practical relevance in the differential diagnosis of mediastinal tumors.

Sodium and potassium channels in epithelial cells from thymus glands and thymomas of myasthenia gravis patients

In both normal and neoplastic epithelial cells from human thymus glands and thymomas, respectively, we found voltage-gated sodium and potassium channels that resemble the adult-type Na channel and the delayed outward rectifier K channel, respectively, of human skeletal muscle and mammalian nervous system. These voltage-gated ion channels might be part of a communication system between epithelial cells and other components of the microenvironment of the thymus.

Cells immunoreactive for neuropeptide in human thymomas.

The presence of opioid peptides, bombesin, and substance P was investigated by immunohistochemistry in tissue sections from six human thymomas. The number of immunoreactive cells seemed to vary from one case to another. Ultrastructural investigation, showing the presence of desmosomes in labelled cells, allowed these cells to be classified as epithelial lineage cells. The occurrence of cells containing neuropeptide in thymomas suggest that peptide molecules could have modulated the behaviour of this tumour, given the reported influence of these molecules on immune functions and their growth promoting activity on several cell types, including mesenchymal and epithelial cells.

Secretion of prostaglandin E by human thymoma MOLT-4 cells and their sensitivity to the cytotoxic action of NK cells

Secretion of prostaglandin E by human thymoma MOLT-4 cells and their sensitivity to the cytotoxic action of NK cells

Distribution of fibronectin and laminin in human thymoma

The distribution of fibronectin and laminin, two extracellular matrix and basement membrane components, was studied in 55 cases of thymoma using immunohistochemistry. The results were compared according to histologic type or clinical stage of the tumor. In addition, electron microscopic observation was done to clarify the extracellular structure of thymoma. Two staining patterns were seen. First, a diffusely or partially intricate network of fibers that contained fibronectin and laminin surrounded tumor cells in 21 out of 55 cases. Most of these cases were spindle cell thymomas and showed low invasive tumors. Second, fibers that contained fibronectin and laminin were restricted only to the septa, blood vessels, and perivascular spaces that did not show a network in the remaining 34 cases. Polygonal cell thymomas showed the latter staining pattern and these were more invasive tumors. We conclude that this network is a characteristic structure of spindle cell thymomas and is related to the invasiveness of the tumor.

Expression and gene rearrangement of the T-cell receptor in human thymomas

Human thymomas are epithelial neoplasms frequently associated with an exuberant lymphoid component. This mixture of epithelial cells and lymphocytes closely mimicks the organization of normal thymic cortex. However, it is not known whether thymocytes in thymoma express the T-cell receptor (TCR) for the antigen. We have analyzed the molecular configuration of TCR genes and their phenotypic expression in eight thymomas. In all we detected polyclonal rearrangements of TCR genes and cytoplasmic expression of TCR molecules in most thymocytes, thus indicating that rearranged TCR genes in thymomas are functioning genes. In addition, these findings suggest that the epithelial component of thymomas, even if neoplastic, is still capable of directing thymocyte differentiation.

Immunohistochemical evidence for enhanced epidermal growth factor receptor expression in human thymomas

Immunohistochemical evidence for enhanced epidermal growth factor receptor expression in human thymomas

Myoid cells in the human thymus and thymoma revealed by three different immunohistochemical markers for striated muscle.

Specimens of human thymus and thymoma obtained from 81 patients including 22 with myasthenia gravis (MG), ranging in age from 10 weeks of gestation to 75 years were examine by the indirect immunoperoxidase technique using three different striated muscle markers: myoglobin, CPK-mm and beta-enolase. Myoid cells ovoid or elongated in shape were distributed in the medulla and showed positive immunoreactions for myoglobin, CPK-mm and beta-enolase by light and electron microscopy. The antigens were first detectable immunohistochemically in the fetus at the 10th week of gestation and showed a relative increase in number and varying distribution patterns with age involution in non-myasthenic thymuses. In MG cases, the number of myoid cells was smaller than in non-myasthenic cases, especially in markedly involuted thymuses. Myoid cells were occasionally observed within thymomas in areas showing medullary differentiation. Small numbers of cells showing a positive immunoreaction for beta-enolase but not for myoglobin and CPK-mm were scattered in the area predominantly composed of epithelial cells. These cells were occasionally positive for keratin and showed desmosome-like structures but no apparent myofilaments, suggesting that muscle-like differentiation of epithelial cells might occur in the neoplastic process of thymoma.

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.

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.

Analysis of lymphocyte phenotype in human thymomas.

Thymomas are tumors originated from the epithelial component of the thymus. This definition according to Rosai and Levine (1) excludes germ cell tumors, malignant lymphomas and neuroendocrine tumors (carcinoids and small cell carninoma). Thymomas are heterogeneous with regard to size, epithelial cell type and the ratio of lymphocyte to epithelial cells (1–3).

Human thymomas: Evidence of immunohistologically defined normal and abnormal microenvironmental differentiation

Fifteen human thymomas were analyzed by immunoperoxidase studies on frozen and paraffin-embedded tissue sections in an attempt to identify the existence of immunologically defined microenvironments. All nine lymphocyte predominant thymomas contained a predominance of lymphocytes bearing the phenotype of cortical thymocytes and dendritic Class II major histocompatibility complex antigen-positive epithelial cells, thus defining cortical-like microenvironments. Medullary-like foci were also seen in all of these cases. Minor phenotypic abnormalities in Leu-2 and -3 antigen expression were seen in three cases. In contrast, the two epithelial predominant thymomas and four mixed thymomas all exhibited features of aberrant microenvironmental differentiation, with only two cases showing demarcation into cortical and medullary foci. A lack of Class II major histocompatibility complex antigens was associated with a decrease in the lymphoid populations and an increase in Leu-1 antigen expression by T cells of otherwise normal cortical phenotype when lymphocytes were present. In contrast, lack of Class I antigen on epithelial cells was not associated with any abnormality in lymphocyte phenotype or microenvironmental organization. We document for the first time abnormal microenvironments in thymomas that may offer insights into understanding normal thymic differentiation.

Acetylcholine-receptor-like protein from human thymoma associated with myasthenia gravis.

Cobrotoxin-binding protein was isolated by affinity chromatography from human thymoma which had been surgically removed from patients with myasthenia gravis. The protein was composed of polypeptides with a molecular mass of 40, 51, 65, and 74 kilodaltons as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulphate. Isoelectric focusing of the protein gave pI values of 5.2-5.6 and 11. This is the first report of the isolation of the protein from human thymoma. These findings suggest that the cobrotoxin-binding protein from human thymoma patients with myasthenia gravis has subunits similar to those of fish electric organs or mammalian muscles.

Relationship between structure and T-lymphocyte maturation in human thymomas. Enzyme histochemical and immunohistological studies.

Twenty-six human thymomas were studied in an attempt to correlate their morphological appearance with the type and degree of T-lymphocyte maturation, as determined by acid alpha-naphthyl-acetate esterase (ANAE) activity and immunological analysis. Four normal human thymuses were used for purposes of comparison. Two morphological patterns were identified in the thymomas. The distinction was based largely on similarities between the neoplastic epithelial cells and normal cortical and medullary epithelial cells, and on the relative proportions of epithelial cells and lymphocytes. By these criteria "medullary" and "cortical" patterns were identified. In several thymomas both patterns were present in the same tumor ("mixed-type pattern"), producing alternating dark cortical-like areas and lighter foci of medullary differentiation. A good correlation was found between the two patterns and the phenotype of the T-associated lymphoid component. ANAE activity, which was completely lacking in normal cortical thymocytes, was almost absent in the phenotypically immature T-cells of cortical-type thymomas. By contrast, in the medullary-type thymomas, T-cells showed immunological features in common with medullary thymocytes. This was characterized by strong ANAE activity in the majority of cells with a staining pattern corresponding to that of peripheral T-lymphocytes. In addition, most of the proliferating epithelial cells in medullary-type thymomas stained strongly with anti-cytokeratin and anti-epidermal-type keratin antisera. In the mixed-type thymomas the epithelial cell morphology and the immunohistochemical and enzymic features of the T-cells were found to be closely related to the respective cortical--or medullary-like areas. It was concluded that the various characteristics of normal thymic cortex and medulla studied are also present in thymomas. In particular, in medullar-type thymomas the presence of many of the features of normal thymic medulla, such as a squamous cell component, macrophages and interdigitating reticulum cells, may constitute a microenvironment which operates actively in T-cell education. This may account for the functional activities, characteristic of peripheral T-lymphocytes, which T-lymphocytes attain in these thymomas.

Phenotypical characteristics and proliferative capabilities of thymocyte subsets in human thymoma

The phenotypical and functional characteristics of the lymphoid component present in ten human thymomas have been analyzed. Thymomas were classified according to the predominant epithelial cell type present in the neoplastic gland. In thymomas of the cortical type a large proportion, clearly higher than that present in mixed thymomas of T6-positive lymphocytes was present. This T6 subset did not proliferate to mitogen but contained almost all thymocytes able to spontaneously proliferate. Higher proportions of T3-positive cells were found in mixed types of thymomas than in cortical-type tumors. This T3 + subset responded to mitogen stimulation and constituted the more mature intrathymic pool. Surprisingly we identified in thymomas a further subset, lacking the cortical and medullary markers T6 and T3, capable of responding to mitogen. The occurrence of higher proliferative responses to phytohemagglutinin (PHA) in the unfractionated population of cells from mixed thymomas than in the cells of cortical thymomas was judged to be attributable to the relatively higher content of both T3-positive and T3, T6-negative thymocytes in the former. Unlike T6 + thymocytes. T3 −T6 − as well as T3 + cells were practically devoid of spontaneous proliferative capacity. The expansion of the intrathymic lymphoid component in human thymomas should then be considered to be attributable to the “spontaneous” proliferative capacity of the T6 + cell pool. In this respect, cortical thymomas not only contained more T6 + cells than the mixed type but also exhibited a higher lymphocyte/epithelial cell ratio and more frequent mitotic figures.