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Immunohistochemical localization of human fascin, a distinct 55-kd actin-bundling protein, was determined for a wide variety of lymphoid tissues (364 specimens total). In non-neoplastic tissues, reactivity was highly selective and localized predominantly in dendritic cells. In the thymus, this protein was distinctly localized to medullary dendritic cells. In reactive nodes, interdigitating reticulum cells of T zones, cells in subcapsular areas, and cells of the reticular network were reactive, with variable reactivity observed for follicular dendritic cells. Splenic dendritic cells of the white pulp and sinus-lining cells of the red pulp were reactive. Endothelial cells of all tissues exhibited variable reactivity. Lymphoid cells, myeloid cells, and plasma cells were uniformly nonreactive. In the peripheral blood, only dendritic (veiled) cells were reactive for fascin. A striking finding was observed for cases of Hodgkin's disease (total 187 cases). In all cases of nodular sclerosis (132), mixed cellularity (34), lymphocyte depletion (2), and unclassified types (5), all or nearly all Reed-Sternberg cells and variants were immunoreactive for fascin. Neoplastic cells exhibited strong diffuse cytoplasmic staining and frequently assumed dendritic shapes, particularly in the nodular sclerosis type, producing an interdigitating meshwork or syncytial network of cells. In cases of mixed cellularity type, neoplastic cells generally appeared more discrete. In all 14 cases of nodular lymphocyte predominance type, L&H variants were nonreactive. By contrast, neoplastic lymphoid cells of only 24 of 156 (15%) other lymphoid neoplasms (127 B cell, 27 T cell, and two null cell evaluated) were reactive for fascin. Fascin represents a highly effective marker for detection of certain dendritic cells in normal and neoplastic tissues, is an extremely consistent marker for Reed-Sternberg cells and variants of Hodgkin's disease (except L&H types), and may be helpful to distinguish between Hodgkin's disease and non-Hodgkin's lymphoma in difficult cases. The staining profile for fascin raises the possibility of a dendritic cell derivation, particularly an interdigitating reticulum cell, for the neoplastic cells of Hodgkin's disease, notably in nodular sclerosis type. However, as fascin expression may be induced by Epstein-Barr virus infection of B cells, the possibility that viral induction of fascin in lymphoid or other cell types must also be considered in Epstein-Barr virus-positive cases.

ME1 is a monoclonal antibody reactive in frozen tissue sections with normal mesothelial cells and malignant mesotheliomas. In this immunoperoxidase study, ME1 reacted with all 40 epithelial type malignant mesotheliomas. Fifty percent or more of the mesothelioma cells were stained in all cases and the staining intensity was strong in 32 and moderate in eight. In contrast, all 19 well- and moderately differentiated pulmonary adenocarcinomas were completely negative, and of the total 88 non-mesotheliomatous malignancies studied, staining comparable to the mesotheliomas was seen in only 6 tumors (2 pulmonary adenocarcinomas, 2 adenocarcinomas of the breast, 1 adenocarcinoma of the pancreas, and 1 melanoma), although limited, weaker staining was seen in additional cases. Five of the six strongly to moderately positive nonmesotheliomatous tumors had immunoreactivity for complementary immunoreactants (CEA, Leu-M1, S-100 protein, HMB-45). Our results with ME1, the first monoclonal antibody that recognizes malignant mesothelial cells, provides a basis for using this reagent in the differential diagnosis of tumors of the pleura and peritoneum.

Intracellular hemoglobin represents an excellent marker for specific characterization of normal, megaloblastic, or dysplastic erythroid cells in paraffin sections. Using an immunoperoxidase indirect sandwich technique for detection of intracellular hemoglobin, erythroid cells at all stages of maturation were readily identified in bone marrow biopsies (58 specimens total) with a) normal erythropoiesis, b) megalobastic erythropoiesis, and c) various myeloproliferative disorders, including erythroleukemia. In other tissues (6 spleens, 2 lymph nodes, 1 liver) with extramedullary hematopoiesis, erythroid cells were similarly defined on the basis of this immunohistochemical method. Initial fixation in Zenker's-acetic acid solution (employed for bone marrow biopsies), B5 solution, or formalin, appeared equally effective in preserving the antigenicity of intracellular human hemoglobin. This sensitive and specific immunoperoxidase technique for erythroid cell characterization is particularly applicable to tissues with abnormal erythropoiesis, in which precise cell identification generally presents a diagnostic problem.

Ultrastructural studies of five T cell immunoblastic sarcomas revealed morphologic features that uniquely distinguished this variant of non-Hodgkin's lymphoma. Immunoblastic sarcomas of T cell type were characterized by large lymphoid cells with striking electron-lucent cytoplasm with few organelles. Neoplastic cells of B cell immunoblastic sarcomas (5 cases) clearly differed, in that they contained numerous cytoplasmic polysomal aggregates and long, irregular strands of rough endoplasmic reticulum, occasionally with dilated cisternae. Light microscopic features were correlated with these ultrastructural distinctions. T immunoblasts correspond to large lymphoid cells with pale to clear cytoplasm, in contrast to B immunoblasts, which exhibit amphophilic cytoplasm and/or plasmacytoid differentiation. These morphologic characteristics may be helpful in identification and classification of immunoblastic sarcomas of T and B cell types.

Intracellular myoglobin represents an excellent marker for specific characterization of normal (adult and fetal) and malignant skeletal muscle cells in paraffin sections. With an immunoperoxidase indirect sandwich technique for detection of intracellular myoglobin, positive staining was observed in 13 of 17 rhabdomyosarcoma specimens including 5 of 7 of the alveolar type, 5 of 5 of the embryonal type, and 3 of 5 of the pleomorphic type. Initial fixation in Zenker's-acetic acid solution gave optimal staining, but satisfactory results were obtained with fixation in formalin, Bouin's, and B5 solutions. Other types of sarcomas (13 cases) and other types of tumors (24 cases) that sometimes mimic rhabdomyosarcoma on histologic examination gave negative results. The immunoperoxidase method affords a sensitive and specific method for identifying rhabdomyoblasts in tissue on the basis of intracellular myoglobin and is of use in distinguishing rhabdomyosarcomas from other sarcomas and from malignant tumors of other types.

The anatomic distribution of smooth muscle myosin, a contractile protein, was determined in a variety of lymphoid tissues (spleen, lymph nodes, tonsils) with the use of highly specific rabbit antibodies to human uterine smooth muscle myosin and an indirect immunoperoxidase technique. In the spleen, in addition to the anticipated immunoreactivity in the walls of arteries, veins, splenic capsule, and trabeculas, other staining patterns were observed. Smooth muscle myosin-containing cells which comprised the adventitia of the trabecular arteries appeared continuous with myosin-containing reticular cells of the white pulp. The latter cells assumed a circumferential pattern within the periarteriolar lymphoid sheaths, then blended delicately with the red pulp at the marginal zone. Ultrastructurally, immunogold techniques demonstrated that smooth muscle myosin in these cells was localized to cytoplasmic filaments. Within the red pulp, a different and distinct staining pattern was observed for the splenic sinuses. Short, regular, orderly, and repetitive bands of immunoreactivity, aligned parallel to the long axis of the sinus, extended between contiguous ring fibers. By immunoelectron microscopy these structures corresponded to distinct bundles of filaments in the endothelial lining cells of the splenic sinuses. Factor VIII associated antigen was also identified in the splenic lining cells in cryostat and paraffin sections, and ultrastructurally. Within the red pulp of the spleen, the sheaths of sheathed capillaries also revealed strong immunoreactivity for smooth muscle myosin. Other sites of immunohistochemical localization of smooth muscle myosin included dendritic reticulum cells present in reactive follicles and in nodular non-Hodgkin's lymphomas. Certain vascular structures, specifically sinus lining cells and Schweigger-Seidel capillary sheaths of the spleen and postcapillary venules of lymph nodes and tonsils, coexpressed smooth muscle myosin and Factor VIII associated antigen. The patterns of localization of smooth muscle myosin are correlated with anatomic structures and possible tissue functions.

Paraffin-embedded tissues of 47 cases of multiple myeloma and 4 cases of macroglobulinemia were studied by the immunoperoxidase indirect sandwich technique for identification of intracytoplasmic immunoglobulin. Specific immunoglobulin with a single heavy and/or light chain was readily detected in the neoplastic cells. Studies were performed on iliac crest bone marrow biopsies which had been fixed and decalcified using Zenker's-acetic acid solution and on tissues from various sites which had been fixed in formalin. An excellent correlation was obtained between the specific immunoglobulin detected intracellularly in the plasma cells or lymphoplasmacytic cells and the monoclonal immunoglobulin found in serum or urine of these cases. The immunoperoxidase technique represents a sensitive and specific method for identifying intracellular immunoglobulin in paraffin-embedded tissues.