Differential diagnosis of genitourinary tumors using monoclonal antibodies to intermediate filament proteins

Definitive diagnosis of poorly differentiated and metastatic neoplasms may be impossible using conventional histologic criteria. Recent developments in cell biology and immunology now enable us to answer such difficult diagnostic problems. Several varieties of structural proteins can be identified in malignant cells using monoclonal antibodies. The composition of these proteins can yield information regarding the origin of a neoplasm. Intermediate filaments are one such family of structural proteins. By characterization of these proteins, using a panel of monoclonal antibodies, poorly differentiated tumors may be definitively classified as carcinomas, sarcomas, lymphomas, or neural tumors. This approach to tumor diagnosis is now applicable to difficult problems in clinical urology.

Analysis of proliferative grade using anti-PCNA/cyclin monoclonal antibodies in fixed, embedded tissues. Comparison with flow cytometric analysis

Cell kinetic information is an important adjunct to histologically-based tumor classifications. Presently, cell kinetic data can be obtained from slide-based material only with monoclonal antibodies such as Ki-67, which require the use of frozen sections and cannot be applied to archival, paraffin-embedded material. Monoclonal antibodies have recently been generated to PCNA/cyclin, a 36 kd, S-phase-associated nuclear protein. The authors investigated whether monoclonal antibody 19A2 could be used to identify proliferating cells within fixed, embedded tissue sections. Deparaffinized sections of 41 methacarn-fixed human tumors were immunostained with 19A2 using a streptavidin biotin immunoperoxidase system. A semiquantitative scoring system was used to evaluate the fraction of cells that were PCNA/cyclin-positive, and this score was compared with cell kinetic data obtained from parallel flow cytometric S-phase analysis that had been performed on fresh samples of the same tumors. While there was general agreement between the slide-based, antibody-derived and the flow cytometrically-derived cell kinetic information, some discrepancies were observed. Some of the latter represented cases in which the anti-PCNA/cyclin antibody preparations demonstrated significant heterogeneity in the numbers of proliferating cells in different regions of the tumor. In other cases, a significant fraction of the positive cells corresponded to nontumor stromal and/or inflammatory cells. In these cases, the slide-based method provided more information about the tumor cell population than did the flow cytometry data. It is concluded that semiquantitative immunocytochemical analysis with anti-PCNA/cyclin antibodies may represent a simple, reproducible, yet powerful technique for the routine analysis of cell kinetic data in alcohol-fixed, paraffin-embedded tissue by the surgical pathologist.

The fibroblast-like nature of myofibroblasts

The myofibroblast is found in normal tissue as well as in a wide variety of pathological processes. We have cultured myofibroblasts and dermal fibroblasts and have found that they secrete similar type-specific procollagens into the culture media. These were primarily type I and III procollagens with a predominance of type I procollagen. These patterns are distinctly different from those of smooth muscle cells, which synthesize predominantly type III procollagen. Cultured fixed cells were also examined by immunohistochemistry. Both myofibroblasts and fibroblasts stained positively with antibodies to type I and III procollagens. Reaction to type V procollagen antibodies was prominent only in the myofibroblast, as was immunostaining with anti-muscle actin antibodies. Immunostaining with desmin antibodies was negative in both cell types. By electron microscopy, the myofibroblast had well-developed dense microfilament fibers of 40-80 degrees that were prominent in the long axes of the cells near the cellular margins. Although the myofibroblast has properties of both smooth muscle cells and fibroblasts, it appears to be most likely a modified fibroblast that has undergone differentiation, probably in response to specific signals from the extracellular matrix.

Hamster thecal cells express muscle characteristics

Contraction of the follicular wall about the time of ovulation appears to be a coordinated event; however, the cells that mediate it remain poorly studied. We examined the theca externa cells in the wall of hamster follicles for the presence of a functional actomyosin system, both in developing follicles and in culture. We used a monoclonal antibody (HHF35) that recognizes the alpha and gamma isoelectric variants of actin normally found in muscle, but not the beta variant associated with non-muscle sources, to evaluate large preovulatory follicles for actin content and composition. Antibody staining of sectioned ovaries showed intense circumferential reactivity in the outermost wall of developing follicles. Immunoblots from two-dimensional gels of theca externa lysates demonstrated the presence of the two muscle-specific isozymes of actin. Immunofluorescence of cultured follicular cells pulse-labeled with [3H] thymidine (for autoradiographic detection of DNA replication) revealed the presence, in many dividing cells, of actin filaments aligned primarily along the longitudinal axis of the cells. In cultures exposed to the calcium ionophore A23187 (10(-4) M) for varying periods (5 min to 1 h), contraction of many individual muscle-actin-positive cells was observed. Immunofluorescence of these cells, fixed immediately after ionophore-induced contraction, revealed compaction of the actin filaments. Our findings demonstrate that the cells of the theca externa contain muscle actins from an early stage and that these cells are capable of contraction even while proliferating in subconfluent cultures. They suggest that follicular growth may include a naturally occurring developmental sequence in which a contractile cell type proliferates in the differentiated state.

Cultured circular smooth muscle from the rabbit colon

Although cultured vascular smooth muscle cells have been extensively characterized and investigated, there are very few studies of cultured intestinal smooth muscle cells. The aim of this study was to culture colonic smooth muscle (CSM) cells from the rabbit colon. Freshly isolated CSM cells from the circular muscle layer of the distal colon were prepared by collagenase digestion. In primary culture, CSM cells attached to the culture vessels by 48 to 72 h, proliferated by 3 to 7 d, and reached confluency by 14 to 17 d with a "hill-and-valley" pattern. Spontaneous contractions were not observed at any time at 21 degrees or 37 degrees C. Confluent primary cultures were greater than 95% CSM cells, as identified by intensely positive immunofluorescent staining to smooth muscle actin-specific CGA7 and muscle-specific HHF-35 monoclonal antibodies. Transmission electron microscopy of freshly isolated and proliferating CSM cells revealed ultrastructural features consistent with smooth muscle cells. We successfully cultured CSM cells of the rabbit from freshly isolated cells and validated these CSM cells by electron microscopy and immunocytochemical staining. These highly pure primary cultures may be used to investigate numerous aspects of CSM cell metabolism and physiology.

Smooth muscle cells can express cytokeratins of "simple" epithelium. Immunocytochemical and biochemical studies in vitro and in vivo

Cytokeratins are a set of 19 proteins that together constitute the class of intermediate filament protein expressed by epithelial cells and tumors. Using a panel of 9 different monoclonal anti-cytokeratin antibodies, the authors have performed immunocytochemistry on methanol-fixed, frozen sections and methacarn-fixed, paraffin-embedded tissue of human myometrial specimens. Anomalous cytokeratin expression (ACE) by smooth muscle cells was found in all specimens. Immunoblots of this tissue confirmed the presence of cytokeratin 19, and possibly 8. In addition, immunocytochemical studies demonstrated ACE in human fetal tissues within the intestinal muscularis and the heart, especially in the region of the aortic outflow tract, and in 8 of 19 cases of leiomyosarcoma from adults. Indirect immunofluorescence studies were also performed on cells explanted from myometrial tissue; the overwhelming majority of cells derived from these cultures were smooth muscle cells as verified by expression of muscle actins, and a subpopulation of these cells was found to be cytokeratin-positive. ACE was confirmed in vitro by double labeling experiments demonstrating simultaneous expression of muscle actins and cytokeratins within the same cell. The significance of this smooth muscle cell ACE is unknown, but it may be a phenotypic marker of smooth muscle in a proliferative state. ACE could be a source of confusion in the immunocytochemical analysis of poorly differentiated malignancies if a complete panel of antibodies is not employed.

Melanoma cell heterogeneity. A study of two monoclonal antibodies compared with S-100 protein in paraffin sections

Fifty-six formalin, Bouin's, and Carnoy's fixed, paraffin-embedded malignant melanomas (21 primary, 35 secondary), were studied by avidin-biotin complex immunohistochemistry using monoclonal antibodies (MoAb) HMB-45 and B1.1, comparing reactivity with polyclonal anti-S-100 protein. B1.1 (anti-CEA MoAb) was expressed in a minor percentage of cells of the invasive component of some primary melanomas, and weak to moderately in scattered metastic melanoma cells. MoAb HMB-45 prepared against melanocytic tumors reacted with over 90% of all tumors studied, being weakly reactive in one, and nonreactive in four metastases. This antibody stained some primary melanomas and their dysplastic nevus components in a heterogeneous manner, but was largely nonreactive in deep dermal nevus cells that were in association with invasive melanoma, enabling recognition of the deepest penetration of melanoma cells in the dermal nevus component. MoAb HMB-45 appears specific for melanoma cells, with no cross-reactivity with nonnevomelanocytic malignant tumors (unlike polyclonal anti-S-100 protein). MoAb HMB-45 is more sensitive in detecting malignant melanoma cell heterogeneity than anti-S-100 protein.

An assessment of human epidermal repair in elderly normal subjects using immunohistochemical methods

The purpose of this study was to document a timetable for selected events of epidermal repair in standard partial thickness incised wounds on the legs of normal elderly human subjects. A Simplate-II bleeding-time device was used for producing the wounds, and immunohistochemical techniques were employed for evaluation of the wounds. Antibodies to filaggrin and Ulex europeus I demonstrated little or no staining on migrating epithelium, but staining was apparent whenever epidermal closure had occurred. Bullous pemphigoid antigen was present in the basement membrane zone at all time points examined, including beneath migrating epithelium, whereas antibodies to laminin and type IV collagen were found only at the most lateral aspects of 2-, 3-, and 5-day wounds. Staining progressed centrally by day 7 and was present as a complete linear band beneath most 14-day wounds. The Simplate-II device provides a standard, easy to use, commercially available, sterile, relatively safe method of producing wounds for systematic studies in humans.

Monoclonal antibodies to intermediate filament proteins: diagnostic specificity in orbital pathology

Intermediate filaments derived from different cell types are antigenically distinct. Monoclonal antibodies to human intermediate filament proteins can, therefore, be used as tissue-specific reagents capable of distinguishing cell type in poorly differentiated neoplasms. We report a case demonstrating the specificity of antiintermediate filament protein antibodies in establishing a difficult orbital diagnosis of esthesioneuroblastoma.

Diagnosis of rhabdomyosarcomas with HHF35, a monoclonal antibody directed against muscle actins

The authors have recently developed a monoclonal antibody, HHF35, that recognizes the muscle-specific isoforms of actin. To determine its potential usefulness in the differential diagnosis of "small, round, blue cell" tumors of childhood, they immunolabeled formalinor B-5-fixed tissue sections from known cases of rhabdomyosarcoma or rhabdomyoma (30), neuroblastoma (9), retinoblastoma (2), and Ewing's sarcoma (9) with HHF35 and with antibodies to creatine kinase M, myoglobin, vimentin, and neuron-specific enolase. HHF35 reacted with 29 of 30 cases of rhabdomyosarcoma, whereas antibodies to creatine kinase M and myoglobin were positive on only 12 and 7 tumors, respectively. HHF35 did not react with any case of neuroblastoma, retinoblastoma, or Ewing's sarcoma when the antibody diluent contained 50 mM EDTA. These results indicate that HHF35 is a highly sensitive and specific marker for myogenic differentiation and that it will be useful in the differential diagnosis of rhabdomyosarcomas.

Thrombospondin in early human wound tissue

We examined partial thickness incised human wounds of 2, 3, 5, 7, and 14 days of age for the presence of thrombospondin by immunostaining and light microscopy. At 2, 3, 5, and 7 days after wounding, thrombospondin is present primarily at the cut edges of the lateral and deep margins of the wound. It appears to be cleared from these extracellular matrix sites, and is no longer detectable in those sites in most 14-day-old wounds. Thrombospondin staining is present, however, in increased amounts around the vascular channels within and adjacent to the 7- and 14-day wounds in increased amounts relative to vascular channels distant from the wound. Our observations are consistent with known in vitro data regarding the binding of thrombospondin to fibrin and components of the extracellular matrix, as well as with data showing that proliferating endothelial cells secrete more thrombospondin than quiescent endothelial cells. These data support the hypothesis that thrombospondin plays a role in the early organization of the extracellular matrix of wounds.

Hepatic veno-occlusive disease after bone marrow transplantation. Immunohistochemical identification of the material within occluded central venules

The authors immunostained autopsy liver tissue from 31 marrow transplant recipients, 19 with hepatic veno-occlusive disease (VOD) and 12 without VOD. A panel of monoclonal and polyclonal antibodies was used to characterize the materials within the occluded venous lesions and to define the location and types of injured cells. Most patients with early VOD (survival less than 50 days, n = 11) had dense periadventitial and intramural immunostaining of terminal hepatic and sublobular central venules (CV) with anti-Factor VIII (9/11) and anti-fibrinogen (4/4) but had no immunostaining with antibody to platelet GPIb. Early VOD patients also had marked loss of Zone 3 hepatocyte cytokeratin (8/9) versus late VOD (1/5) or non-VOD (2/7). Patients with late VOD lesions (n = 8, survival greater than 50 days) had increased collagen within occluded VOD lesions. Type III much greater than Type I, and increased sinusoidal collagens Types I, III, and IV. These studies and other data suggest the following events in the genesis of VOD. Initial injury to endothelium of CV and/or sinusoids and possibly also to Zone 3 hepatocytes triggers the coagulation cascade in the periadventitial zone of CV. The late sequela, collagenous CV occlusion, results from activated mural myofibroblasts and/or embolized Ito cells and hepatocytes.

HHF35, a muscle actin-specific monoclonal antibody. II. Reactivity in normal, reactive, and neoplastic human tissues

Monoclonal antibody HHF35 has previously been characterized biochemically as recognizing isotypes of actin (alpha and gamma) which are specific to muscle cells. In this study, the authors have investigated the normal and pathologic tissue distribution of HHF35-positive cells using the avidin-biotin immunoperoxidase method on methacarn-fixed, paraffin-embedded sections of human tissue. In addition to muscle tissues (smooth, skeletal, and cardiac) the antibody localizes to myoepithelium, as well as most of the capsular cells of several parenchymal organs, including liver, kidney, and spleen, with extension of the latter cells into the splenic trabeculaes. In pathologic tissues, the antibody localizes to cells, identified by some investigators as "myofibroblasts," in the stroma of certain tumors, within hyperplastic fibrous tissue responses ("fibromatoses") such as Dupuytren's contracture, and within fibrotic lung tissue. HHF35 also localizes to cells that proliferate within the intima in lesions of atherosclerosis and to a unique population of reactive mesothelial and submesothelial cells. Among tumors, it is positive only on leiomyomas, leiomyosarcomas, and rhabdomyosarcomas, and negative on all nonmuscle sarcomas. This antibody thus shows great potential utility as a diagnostic reagent in various pathologic conditions, most especially in the diagnosis of tumors of muscle origin.

Correlative light and electron microscopic immunocytochemistry on the same section with colloidal gold

Ultrastructural localization of growth hormone in rat anterior pituitary and of muscle-specific actin in rabbit arterial smooth muscle cells was accomplished with a post-embedment procedure using colloidal gold. Plastic sections (2 microns) were mounted on slides, deplasticized, immunostained with immunoglobulin-colloidal gold particles, re-embedded in Epon, and sectioned for electron microscopy. This procedure enabled light and electron microscopic localization of these intracellular antigens on the same section. Positive immunostaining was demonstrated with this procedure with a muscle-specific actin antibody which previously failed to localize antigenic sites by EM. The procedure described yielded staining of high specificity, with minimal background and well-preserved ultrastructure. This re-embedding technique is useful in situations where problems with post-embedding EM immunostaining exist and where correlative LM and EM immunostaining is essential.

Characterization of two monoclonal antibodies to human epidermal keratohyalin: reactivity with filaggrin and related proteins

Two monoclonal antibodies (AKH1 and AKH2) were elicited with partially purified human filaggrin and characterized by immunohistochemistry on normal and abnormal skin biopsies, immunoblotting techniques, and antigen purification. Both antibodies react strongly with the granular cell layer consistent with the distribution of keratohyalin and show a more diffuse reaction with the stratum corneum in normal skin biopsies. Reaction in cultured human keratinocytes is limited to immunofluorescent granules in flattened, well-differentiated cells in confluent cultures, in which we have previously demonstrated keratohyalin. On immunoblots AKH1 reacts with filaggrin (37 kD) and profilaggrin (400 kD), while AKH2 primarily stains bands of 150 and 300 kD. The AKH2 antigens were identified in the cationic protein fraction used for immunization and were purified by gel permeation and high-performance liquid chromatography. Amino acid composition of these proteins differs only slightly from filaggrin. Immunohistochemical staining patterns of the two antibodies are very similar in the genetic disorders of keratinization tested, except for ichthyosis vulgaris, and reflect the presence and distribution of keratohyalin. In ichthyosis vulgaris, AKH1 staining is weak, consistent with the morphology and with biochemical absence of profilaggrin/filaggrin; however, AKH2 staining is positive, although weaker than normal, suggesting the presence of the AKH2 antigens even when keratohyalin is absent or abnormal. Antibodies AKH1 and AKH2 may be useful as differentiation markers for keratinization in tissues and for cells in culture. Antibody AKH1 can be used specifically for detection of profilaggrin/filaggrin in tissues, cultured keratinocytes, and extracts.

Diagnosis of orbital and periorbital tumors. Use of monoclonal antibodies to cytoplasmic antigens (intermediate filaments)

Histopathology provides a definitive diagnosis in the majority of orbital and periorbital tumor biopsies. Occasionally, a tumor cannot be diagnosed by conventional histopathologic means, or the diagnosis is suspect. Special stains have been the primary diagnostic alternative in the past; more recently they have been supplemented with electron microscopy. Immunocytochemistry, classification using monoclonal antibodies to specific cellular antigens, has added a new modality to pathologic diagnosis. Immunocytochemistry can aid in diagnosis in three ways: (a) suggestion of a firm diagnosis, (b) selection from a histopathologic differential, or (c) direction for further evaluation such as special stains or electron microscopy. Immunocytochemistry rarely provides a definitive diagnosis but instead confirms the histopathologic diagnosis. Intermediate filaments are cytoplasmic antigens to which monoclonal antibodies are available. Five antigenically distinct groups of intermediate filaments can help classify tumors derived from mesenchymal, muscle, epithelial, glial, or neural cells. Six cases of orbital or periorbital tumors are presented, which demonstrate the usefulness of intermediate filament immunocytochemistry for classification or confirmation of a histopathologic diagnosis.

HHF35, a muscle-actin-specific monoclonal antibody. I. Immunocytochemical and biochemical characterization

A monoclonal antibody to muscle cell actin isotypes was produced and characterized. Immunocytochemical analysis of methanol-Carnoy's-fixed, paraffin-embedded human tissue revealed that this antibody, termed HHF35, reacts with skeletal muscle cells, cardiac muscle cells, smooth muscle cells, pericytes, and myoepithelial cells, but is nonreactive with endothelial, epithelial, neural, or connective tissue cells. When assayed by indirect immunofluorescence, HHF35 reacts with microfilament bundles from various cultured mammalian smooth muscle cells, but does not react with cultured human dermal fibroblasts or various epithelial tumor cell lines. In one-dimensional gel electrophoresis immunoblot experiments this antibody detects a 42-kd polypeptide from tissue extracts of uterus, ileum, aorta, diaphragm, and heart and extract from smooth muscle cells. The antibody also reacts with a comigrating 42-kd band of highly purified rabbit skeletal muscle actin. HHF35 is nonreactive on immunoblots of extracts from all tested nonmuscle cell extracts. Immunoelectrophoresis followed by immunoblotting performed in the presence of urea and reducing agents reveals recognition of the alpha isoelectrophoretic variant of actin from skeletal, cardiac, and smooth muscle sources and of the gamma variant from smooth muscle sources. Because HHF35 reacts with virtually all muscle cells, it will be useful as a marker for muscle and muscle-derived cells.

Stromal cells from human long-term marrow cultures, but not cultured marrow fibroblasts, phagocytose horse serum constituents: studies with a monoclonal antibody that reacts with a species-specific epitope common to multiple horse serum proteins

This report describes an IgG1 mouse monoclonal antibody derived after immunization of mice with washed stromal cells from human, long-term bone marrow cultures. The antigen recognized by the antibody (BMS-1) is a carbohydrate-containing prosthetic group that is common to and specific for multiple horse serum proteins. These proteins are avidly ingested by stromal cells and concentrated in endocytic vesicles. Cultured smooth muscle cells took up the horse proteins in a similar manner to marrow stromal cells while cultured marrow fibroblasts, endothelial cells, and hepatoma cells did not. These data indicate that marrow stromal cells specifically accumulate horse serum proteins which might partially explain the horse serum requirement for long-term marrow culture maintenance. The data also suggest further similarities between marrow stromal and smooth muscle cells and additional differences between marrow fibroblasts and marrow stromal cells.

Fatty streak expansion and maturation in Watanabe Heritable Hyperlipemic and comparably hypercholesterolemic fat-fed rabbits

This study focuses on the expansion and maturation of the fatty streak in the aorta of Watanabe Heritable Hyperlipemic rabbits and comparably hypercholesterolemic fat-fed rabbits between 2 and 6 months duration of hypercholesterolemia. In both groups of animals, the fatty streaks expanded due to: 1) the formation of multiple layers of a mixed population of macrophage-derived foam cells and lipid-containing smooth muscle cells, 2) the hypertrophy of the macrophage-derived foam cells, 3) the continued accumulation of extracellular matrix, 4) the insudation of plasma components. Immunocytochemical studies utilizing macrophage-specific and muscle-actin-specific monoclonal antibodies indicated that the expanding and mature fatty streaks in both the Watanabe and fat-fed rabbits were primarily composed of macrophage-derived foam cells. Hypertrophy of those foam cells situated immediately beneath the endothelium was associated with retraction of the endothelium and exposure of the intimal foam cells to the circulation. Endothelial retraction with exposure of intimal foam cells may facilitate entry of blood cells and lipoproteins into the lesions and formation of mural thrombi on the surfaces of the exposed cells. Biochemical analyses of the cholesterol content of the arteries indicated that both unesterified cholesterol and cholesteryl esters were deposited to a comparable degree in both the Watanabe and fat-fed rabbits. Thus, the absence of the low density lipoprotein receptor in Watanabe rabbits does not appear to directly influence the accumulation of cholesterol in the artery wall.

Fatty streak initiation in Watanabe Heritable Hyperlipemic and comparably hypercholesterolemic fat-fed rabbits

Morphologic and immunocytochemical studies were conducted to determine the sequence of cellular interactions that occur during the initiation of the fatty streak in the aorta of Watanabe Heritable Hyperlipemic rabbits and comparably hypercholesterolemic fat-fed rabbits. Watanabe rabbits from 3.5 weeks gestation to 2 months of age and fat-fed rabbits from 1 week to 2 months duration of hypercholesterolemia were compared utilizing light microscopic and scanning and transmission microscopic techniques. In both groups of animals, the earliest detectable events were an increase in monocyte adherence and subendothelial migration followed by formation of a single layer of intimal macrophage-derived foam cells. Immunocytochemical studies using macrophage-specific and muscle-actin-specific monoclonal antibodies support the morphologic data which suggests that the early fatty streak in both the Watanabe and fat-fed rabbits is predominantly composed of macrophage-derived foam cells. Thus, the absence of functional low density lipoprotein receptors in the Watanabe rabbit and differences in the distribution of cholesterol among the lipoproteins in the Watanabe and fat-fed rabbits do not appear to alter the initial responses of the cells of the artery wall to chronic hypercholesterolemia.

Immunocytochemical analysis of cellular components in atherosclerotic lesions. Use of monoclonal antibodies with the Watanabe and fat-fed rabbit

We have performed immunocytochemical investigations into the distribution of smooth muscle cells and macrophages in the atherosclerotic lesions of the Watanabe heritable hyperlipidemic (WHHL) and fat-fed rabbits. We used monoclonal antibodies specific for muscle cells and macrophages, the latter with a new macrophage-specific monoclonal antibody designated RAM11. Scattered macrophages were observed in the subendothelium in areas of grossly normal aorta. Raised lesions were divided into four major groups, based on qualitative aspects of cell localization: fatty streak, composed predominantly of macrophages; intimal thickening, composed predominantly of smooth muscle cells that displayed considerable morphological heterogeneity with an admixture of macrophages; early fibrous plaques, characterized by approximately equal numbers of smooth muscle cells and macrophages; advanced fibrous plaques, composed of a fibrous cap containing flat smooth muscle cells overlying a macrophage-rich zone of atheromatous debris. These studies demonstrate the nature of the lesions in the two rabbit models and the usefulness of monoclonal antibodies in analyzing the cellular composition of atherosclerotic lesions.

Unique proteins defined by monoclonal antibodies specific for human melanoma. Some potential clinical applications

A panel of monoclonal antibodies, designated HMB 18, 45, and 50, have been isolated that are highly specific for malignant melanoma. When tested on fixed, paraffin-embedded tissue sections, they reacted with 97 percent of melanomas tested (58 of 60), including pigmented, unpigmented, primary, and metastatic melanoma. The specificity in differentiating melanomas from other malignant tumors, including 112 carcinomas, 35 lymphomas, and 39 sarcomas, was 100 percent. Normal melanocytes were unreactive, although some benign melanocytic lesions were recognized. Using immunoprecipitation and SDS-PAGE analysis of 35S-methionine-labeled melanoma cells in tissue culture, a previously undescribed protein of approximately 10 kd was recognized by all three antibodies. HMB 50 also precipitated two high molecular weight proteins of 97 kd and 110 kd from the conditioned medium of melanoma cells. These monoclonal antibodies are the most sensitive and specific antibodies generated against human melanoma to date. Their clinical application in diagnostic surgical pathology and potential use in immunotherapy are discussed.

Human atherosclerosis. II. Immunocytochemical analysis of the cellular composition of human atherosclerotic lesions

The authors have performed immunocytochemical investigations of the distribution of various cell types in human atherosclerotic plaques using monoclonal antibodies specific to smooth muscle cells (CGA7 [Gown et al, J Cell Biol 1985, 100:807-813] and HHF35 [Tsukada et al, Am J Pathol (In press)] ); lymphocytes (T200 antigen); endothelial cells (Factor VIII and the Ulex europeus agglutinin); and macrophages, the latter with a new macrophage-specific antibody HAM56. All studies were performed on methanol-Carnoy's-fixed, paraffin-embedded tissues. In areas of grossly normal aorta, significant numbers of macrophages were noted within areas of diffuse intimal thickening. The cellular composition of the following three types of raised lesions were analyzed: fibro-fatty lesions, which, despite their gross appearance, consistent with fibrous plaques, were composed almost exclusively of macrophages and lymphocytes and almost devoid of smooth muscle cells; fibrous plaques, which were predominantly composed of smooth muscle cells displaying considerable morphologic heterogeneity and an admixture of blood-borne cells; advanced plaques, which were characterized by complex layers of smooth muscle cells and macrophages with considerable variation from region to region. Also noted were foci of medial and even intimal vascularization subjacent to the more advanced plaques. These studies demonstrate the application of monoclonal antibody technology to the study of the cellular composition of human atherosclerotic lesions.

Monoclonal antibodies specific for melanocytic tumors distinguish subpopulations of melanocytes

The authors have generated monoclonal antibodies to an extract of melanoma. When tested on a variety of fixed, embedded sections of malignant tumors, one antibody (HMB-45) reacted with 60 of 62 melanomas and none of 168 nonmelanomas (carcinomas, lymphomas, and sarcomas). The antibody reacts with junctional nevus cells but not intradermal nevi, and recognizes fetal and neonatal melanocytes but not normal adult melanocytes. This antibody thus demonstrates absolute specificity for melanocytic tumors and thus has great utility for the surgical pathologist in distinguishing among poorly differentiated tumors of uncertain origin. It also identifies differences among populations of melanocytes which may be useful in understanding the biology of and interrelationships between these cells.