Metaplastic carcinoma of the thymus is a distinct clinicopathological entity that should be distinguished from the usually benign medullary thymomas and from the clinically aggressive carcinosarcomas and sarcomatoid carcinomas.

We report on three resected cases of intrapulmonary plasma cell granuloma. All of them were asymptomatic. One of them showed bilateral multiple lesions and in this case bilateral partial resections of lung in one stage were performed. Under light and electron microscopy the lesions were composed of plasma cells and other kinds of inflammatory cell. The plasma cells were mature and had rich endoplasmic reticulum but no kind of intracytoplasmic inclusion. Steroid therapy was effective for the recurrent lesion after the operation.

Histologically normal thymus (type A) in patients with myasthenia gravis (MG) was immunohistochemically compared with hyperplastic MG thymus (type B) and normal non-MG thymus. In formalin-fixed, paraffin-embedded sections of ten type A, ten type B, and eight non-MG cases, the thymic epithelium and other cellular components were stained in conjunction with the basement membrane by a double immunoenzymatic method. This technique demonstrated a moderate architectural disturbance in type A thymus, with distended perivascular space (PVS), elongated medullary epithelium, and disrupted basement membrane. These changes were more prominent in type B thymus but were minimal to lacking in non-MG thymus. Compared with those in non-MG thymus, the myoid cells in MG thymuses of both types tended to cluster around the Hassall's corpuscles, with a slight decrease in number in type B but not in type A. B-lymphocytes were present in type B, type A, and non-MG thymuses in that order of abundance; the cells were confined to the medullary parenchyma in the non-MG group but were numerous both in the PVS and medulla in the MG groups. T-lymphocytes were increased in the expanded PVS of type A and B MG thymuses. The number of interdigitating reticulum cells was similar in the three groups, but the cellular distribution was more dispersed in MG thymuses of both types. These findings, although previously described in type B thymus, have not been well recognized in type A thymus. They support the view that a common abnormality (presumably chronic thymitis), differing in degree only, underlies MG thymuses regardless of the presence of follicular hyperplasia.

Fourteen thymomas were studied by electron microscopy and immunohistochemistry. Based on the ultrastructure of the neoplastic epithelial cells in comparison with normal thymic epithelium, four cortical-, three mixed-, five medullary-, and two corpuscular-type tumors were categorized. Histologically the tumors of cortical type showed prominent lymphocytic infiltration, but scant interdigitating reticulum cells (IDCs) were demonstrated by immunoperoxidase method on paraffin sections with anti-S-100 protein antiserum. Fewer lymphocytes but more IDCs were present in the tumors of medullary and corpuscular types, although variable in those of mixed type. This corticomedullary difference among thymomas was confirmed in some of them by the immunoperoxidase method on frozen sections with monoclonal antibodies. The cortical-type tumors were HLA-DR positive in tumor cells and infiltrated predominantly with cortical thymocytes (OKT-6+, OKT-3-, both Leu 3a/3b+ and OKT-8+), whereas the medullary- and corpuscular-type tumors were HLA-DR positive primarily in IDCs but not in tumor cells and were infiltrated more with medullary thymocytes (OKT-6-, OKT-3+, either Leu 3a/3b+ or OKT-8+). The classification of thymomas based on neoplastic epithelial cells will serve to refine the traditional classification based on reactive lymphocytes.

Summary Eleven cases of histiocytic necrotizing lymphadenitis were studied. Originally four were misdiagnosed as cervical tuberculous lymphadenitis. The characteristic symptoms and signs were local tenderness, fever, leucocytopenia and good prognosis. Antibody to Epstein-Barr virus was elevated in 2 of 3 cases. Biopsy of the affected lymph node was necessary when the differential diagnosis from lymph node tuberculosis or malignant lymphoma could not be made. The characteristic histological feature was focal necrosis without neutrophil infiltration in cortical or subcortical areas. Ultrastructurally, we found characteristic inclusions (‘tubulo-reticular structures’) in histiocytes and lymphocytes.

The cytologic phenotypes of 20 well-differentiated pulmonary adenocarcinomas were determined by electron microscopy. On examination of more than 100 cells in each case, the tumors were classified according to the predominant cell types. Nine cases (45%) were of mucous cell type, further divided into 7 cases of bronchial surface epithelial cell type, 1 case of bronchial gland cell type, and 1 case of metaplastic bronchiolar goblet cell type. The remainder included 5 cases (25%) of Clara cell type, 2 cases (10%) of type II cell type, and 4 cases (20%) of mixed cell type. The predominant histologic pattern by light microscopy was "typically" bronchioloalveolar (Manning et al.'s type 1) in the metaplastic goblet cell tumor and papillary in most Clara cell-type tumors, while it was glandular in bronchial surface and bronchial gland cell types, although variable in type II cell or mixed cell type. Therefore, bronchioloalveolar carcinomas, when histologically defined inclusive of papillary tumors, present cytologic phenotypes also related to the bronchioloalveolar epithelium, i.e., metaplastic goblet or Clara or type II cell subtypes, which is in accordance with some previous reports. These tumors could be distinguished from the other (glandular) adenocarcinomas that show primarily bronchial mucous cell differentiation.

Clinical and immunological changes in patients with myasthenia gravis (MG) who had extended thymectomy (Tx) and/or corticosteroid therapy were examined to elucidate the mechanisms of improvement following the treatments. The changes found were: 1) After Tx and steroid therapy, in patients with MG whoshowed clinical improvement, the CD4/CD8 ratio and B lymphocyte subpopulations were markedly decreased. 2) Linear correlations between two T-cell subsets were evident in CD3against CD4 and CD4/CD8 against CD4after both Tx and steroid therapy. 3) T lymphocytes-CD8 decreased immediately after Tx and returned to pre-treatment levels within three weeks. 4) Cellular sensitization against a nicotinic acetylcholine receptor(AChR)-like protein isolated from fetal calf thymus decreased after steroid therapy. These results indicate that clinical improvement in MGafter the treatments was accompanied by a decrease in helper/ inducer T lymphocytes, B lymphocytes and specific lymphocyte sensitization against nicotinic AChR.

Abstract. The localization of the nicotinic acetylcholine receptor-like protein (nAChR-LP) in seven human thymi with lymphofollicular hyperplasia and four thymomas from patients with myasthenia gravis (MG) were studied using the polyclonal antibody against nAChR-LP from a fetal calf thymus. By immunoelectron microscopy in both normal thymi and thymi from patients with MG, nAChR-LP was found in the tonofilaments and the plasma membrane of mainly the secretory-type cells of Hassall's corpuscles and some medullary epithelial cells. This finding is the first confirmation of the epithelial nature of the nAChR-LP positive cells in the outer rim of Hassall's corpuscles by immunoelectron microscopy. The positive cells also showed reactivity with anti-major histocompatibility complex (MHC)-class II antibody. These findings suggest that the nAChR-LP positive cells in Hassall's corpuscle and the thymic medulla are responsible for the induction of autoimmunity in MG.