Ki-M6 immunostaining in routinely processed sections of reactive and neoplastic human lymphoid tissue

A monoclonal antibody, termed Ki-M6 (CD68), which shows a restricted reactivity to cells of the monocyte/macrophage system, has been evaluated primarily with the use of cryostat sections. In this study the authors could assess that the Ki-M6 antibody recognizes a fixation-resistant epitope in most human macrophages. The Ki-M6 immunoreactivity with monocyte/macrophage-related cells was established by testing on routinely processed samples of reactive and neoplastic lymphoid tissues; it was compared with the staining for vimentin (V9) and S-100 protein antibodies, with visualization of the stationary elements of lymphoid tissues, with the aim of establishing its value in the study of the nonlymphoid microenvironment. The Ki-M6 antibody reactivity could be achieved with Bouin-fixed, paraffin-embedded tissue sections, without any proteolytic treatment, with the use of the avidin-biotin complex (ABC) method, especially after overnight incubation time at 4 degrees C. Some reduction in antigenic reactivity was observed in B5- or formaldehyde-fixed samples. The antibody reacted with macrophages of all different lymph node compartments; a broad reactivity against cells of macrophage lineage, including multinucleated giant cells, was observed in epithelioid granulomas. Ki-M6-positive cells other than classic macrophages were the so-called "plasmacytoid T-cells" and cells displaying elongated cytoplasms with fibroblastic-like features. Granulocytes, follicular dendritic reticulum cells, and interdigitating reticulum cells did not reveal any reactivity with Ki-M6 antibody. In malignant lesions, neoplastic cells of follicular and diffuse B- and T-cell lymphomas, including large cell non-Hodgkin's lymphomas, and Reed-Sternberg cells of Hodgkin's disease were negative in all cases studied. This study shows that Ki-M6 seems to be another anti-macrophage-specific antibody that reacts, in routinely processed tissue sections, with tissue macrophages but not with accessory cells. Thus, it may be a valuable addition to vimentin and S-100 protein antibodies for investigation of the microenvironmental organization of lymphoid tissues both in normal and neoplastic conditions.     

Immunostaining in atypical fibroxanthoma of the skin

We have studied 12 cases of cutaneous atypical fibroxanthoma using immunohistochemistry to demonstrate lysozyme, alpha-1-antitrypsin, S-100-protein, receptors for peanut agglutinin, and intermediate filaments. Results were compared with immunostaining in 24 cases of other so-called fibrohistiocytic tumours. In addition 2 cases of atypical fibroxanthoma and 6 cases of fibrohistiocytic tumours were stained by monoclonal antibodies specific for the monocyte cell lineage (Ki-M1, Ki-M2, Ki-M6, Ki-M7, Ki-M8, OKM-1 and Leu-M1) and double-stained by monocyte-markers and Ki-67. The immunophenotype of atypical fibroxanthoma was rather similar to the marker profile found in malignant fibrous histiocytoma. All atypical fibroxanthomas were positive for vimentin and negative for epithelial markers. Monocyte lineage-specific determinants could be demonstrated in varying amounts in cells suggestive of being reactive. In contrast proliferating--Ki-67 positive--cells did not express monocyte/macrophage related antigens in atypical fibroxanthoma and malignant fibrous histiocytoma both. As to the histogenesis of these tumours our findings speak in favour of a derivation from primitive mesenchymal cells rather than from histiocytes.     

PG-M1: A New Monoclonal Antibody Directed against a Fixative-Resistant Epitope on the Macrophage-Restricted Form of the CD68 Molecule

A new anti-macrophage monoclonal antibody (PG-M1) was produced by immunizing BALB/c mice with fresh spleen cells from a patient with Gaucher's disease. PG-M1 reacts strongly with a fixative-resistant epitope of an intracytoplasmic molecule, selectively expressed by virtually all macrophages of the human body. Although attempts to immunoprecipitate the molecule recognized by PG-M1 have failed so far, the reactivity of the antibody with COS-1 and WOP cells transfected with a human complementary DNA clone encoding for the CD68 antigen suggests that PG-M1 is a new member of the CD68 cluster. However, unlike other CD68 antibodies (KP1, EBM11, etc.), which react with both macrophages and myeloid cells, PG-M1 detects a fixative-resistant epitope on the macrophage-restricted form of the CD68 antigen. In 957 routinely fixed, paraffin-embedded samples, PG-M1 showed a more restricted reactivity with elements of the monocyte/macrophage lineage than the previously described monoclonal antibodies MAC-387 (anti-calgranulins), KP1 (CD68) and Ki-M1P. Among hematological malignancies, PG-M1 only labels acute leukemias of M4 and M5 type and rare examples of malignant histiocytosis/true histiocytic sarcoma. In contrast, acute leukemias of the M1, M2, M3, M6, M7, and L1-L3 types, non-Hodgkin's lymphomas, and Hodgkin and Reed-Sternberg cells of Hodgkin's disease are consistently PG-M1-negative. In the daily diagnostic practice, PG-M1 seems to be particularly valuable for the diagnosis of myelomonocytic or monocytic leukemia and neoplasms of true histiocytic origin in routine paraffin sections.     

Monocyte/macrophage-reactive monoclonal antibody Ki-M6 recognizes an intracytoplasmic antigen.

A monoclonal antibody, termed Ki-M6, is described, which shows a restricted reactivity to cells of the monocyte/macrophage system. On light- and electron-microscopic immunoperoxidase staining Ki-M6 recognizes monocytes and the phagocytosing compartment of macrophages residing in different tissue sites; granulocytes and the so-called immune accessories of B- and T-cell immune response as closely monocyte/macrophage related cell populations do not reveal any reactivity. This is shown by comparison with the monoclonal antibodies Ki-M4 and Ki-M1 or OKT6 recognizing immune accessory cells by immunohistochemical methods. Ki-M6 binds to a lysosomal membrane-restricted antigen of 60,000 daltons without influencing significantly lysosome-related functions as far as the chemiluminescence response is concerned.     

Ber-MAC3: new monoclonal antibody that defines human monocyte/macrophage differentiation antigen.

A new monoclonal antibody Ber-MAC3 is reported. It recognises a formol sensitive epitope of a not yet clustered monocyte/macrophage specific 140 kilodalton glycoprotein that is expressed on the cell surface and in the cytoplasm. In 30 cases of acute and chronic leukaemia, Ber-MAC3 staining was restricted to 15 myeloid leukaemias of M4 and M5 types. The tumour cells of two cases of true histiocytic malignancies were Ber-MAC3 positive, whereas those of all 280 malignancies of lymphocytic origin were negative. The latter included 52 cases of Hodgkin's disease and 41 cases of Ki-1 positive anaplastic large cell lymphomas which had previously been classified as true histiocytic lymphomas. Ber-MAC3 therefore seems to be of considerable value for selective identification of monocytes and macrophages at a certain stage of differentiation and seems to be suitable for diagnosing myelomonocytic or monocytic leukaemia and neoplasms of true histiocytic origin.     

Diversity of the human monocyte/macrophage system as detected by monoclonal antibodies

Four monoclonal antibodies against the human monocyte/macrophage system, termed Ki-M1, Ki-M6, Ki-M7, and Ki-M8, are described with regard to their immunohistochemical tissue distribution pattern and their subcellular reactive sites. The differences found applying these analyses are also reflected by the various molecular weights of the recognized antigens. Based on these data it is proposed that the monocyte/macrophage system can be divided into the phagocytosing compartment on one hand and the immune accessory compartment on the other hand; the latter constitutes the interdigitating reticulum cells, the indeterminate dendritic cells, and the Langerhans cells, as well as the follicular dendritic cells (dendritic reticulum cells) as the accessory cells for T- and B-cell immune response, respectively.     

Diagnosis of myelomonocytic and macrophage neoplasms in routinely processed tissue biopsies with monoclonal antibody KP1.

A new monoclonal antibody, KP1, against the CD68 antigen, which labels macrophages and other members of the mononuclear phagocyte lineage in routinely processed tissue sections, has been used to stain a range of lymphoid, histiocytic, and myelomonocytic proliferations. All 20 neoplasms of myeloid, myelomonocytic, and presumed macrophage derivation reacted with antibody KP1. None of the 22 cases of T cell neoplasia had positive reactions. Although 14 of 41 B lineage lymphomas and leukaemias were stained by antibody KP1, staining was usually confined to small dots of reactivity, in contrast to the strong and extensive cytoplasmic staining seen in the neoplasms of myeloid and macrophage/monocyte origin. Furthermore, positive B cell neoplasms were almost all small cell proliferations, which are unlikely to be confused with myelomonocytic malignancies. It was concluded that antibody KP1 is a valuable addition to a panel of monoclonal antibodies for phenotyping lymphomas, particularly in routinely fixed tissues. It should assist the pathologist in the recognition of extramedullary presentation of leukaemia, aid in the diagnosis of suspected cases of true histiocytic neoplasia, and allow for quantitation of macrophages infiltrating lymphomas and other solid tumors.     

Characterization of tumor cells in malignant fibrous histiocytomas and other soft-tissue tumors, in comparison with malignant histiocytes. II. Immunoperoxidase study on cryostat sections.

The authors have investigated a possible relationship between tumor cells of malignant fibrous histiocytomas (MFHs) and histiocytes. This relationship was studied by means of immunophenotyping using monoclonal antibodies specific for the monocyte cell lineage (FMC-17, Mac-1, OKM-1, Leu-M1, and lysozyme) and mono- and polyclonal antibodies specific for fibroblasts (respectively, FIB-86 and FSG). The immunophenotypes of the MFH tumor cells were compared with those of tumor cells of "true" histiocytic tumors. Monocyte lineage-specific determinants could be demonstrated in varying amounts on cells of the "true" histiocytic tumors but not on cells of MFH or other soft-tissue tumors. The reverse was true for determinants on fibroblasts. The absence of these determinants on malignant histiocytes, and their presence on MFH (and also on benign fibrous histiocytomas, fibrosarcomas, schwannomas, osteosarcomas, hemangiosarcomas, leio- and rhabdomyosarcomas) supported the conclusion that MFH tumor cells originate from mesenchymal cells which do not belong to the mononuclear phagocytic system. Subdivision of the MFH tumors revealed that the storiform-pleomorphic subtypes could express HLA-Dr/Ia antigens, like histiocytic tumors. The inflammatory cell subtype, however, lacked these antigens.     

Analysis of large-cell lymphomas using monoclonal and heterologous antibodies.

Fifteen cases of large-cell lymphoma, diagnosed as centroblastic (5), B-immunoblastic (5) or true histiocytic (5). lymphoma and one case of malignant histiocytosis were studied with monoclonal antibodies. Each diagnosis was based on morphological as well as marker studies. A panel of monoclonal and heterologous antibodies against T lymphocyte differentiation antigens (Leul, Leu2a, Leu3a, OKT4, OKT8, TA1), B lymphocyte subsets (BA1, BA2, HLA-DR, alpha C3b receptor antiserum, surface immunoglobulins), the common acute lymphoblastic leukaemia antigen (CALLA), monocytes/macrophages (OKM1, anti-human monocyte 1, TA1, Mac1, HLA-DR, anti-C3b receptor), myeloid cells (VIM-D5, elastase, OKM1) and the cells of the Langerhans cell/interdigitating reticulum cell series (OKT6, NA1/34). The results show a specific staining pattern for true histiocytic lymphoma (histiocytic sarcoma). Centroblastic and B-immunoblastic lymphomas showed gradual differences with mostly strong staining for HLA-DR and weak with anti C3b receptor for B-immunoblastic lymphomas in contrast to centroblastic lymphomas. Staining with BA1 and BA2 indicated immunological heterogeneity in these lymphomas. The number of admixed cells was usually low with few B cells and a shift in the ratio helper/inducer to suppressor/cytotoxic T cells in favour of the suppressor/cytotoxic subset.     

KP1: a new monoclonal antibody that detects a monocyte/macrophage associated antigen in routinely processed tissue sections.

A new monoclonal antibody, KP1, raised against a lysosomal fraction of human lung macrophages, recognises a fixation-resistant epitope in a wide variety of tissue macrophages (such as Kupffer cells germinal centre, splenic, and lamina propria macrophages), and in granulocyte precursors. Its broad reactivity with cells of the mononuclear phagocytic lineage was established by testing on routinely processed samples of normal and reactive lymphoid tissues. Interdigitating reticulum cells were unstained or showed limited cytoplasmic staining while Langerhans' cells and follicular dendritic reticulum cells were unreactive. KP1 recognises a molecule of about 110 kilodaltons in macrophage-rich human tissue when tested by either immunoprecipitation or Western blotting (although the latter procedure also shows two additional components with molecular weights of 70 and 40 kilodaltons). KP1 should be of considerable value for studying disorders of the monocyte/macrophage system, including both reactive and neoplastic states (such as true histiocytic proliferations).     

Immunologic marker analysis of normal and malignant histiocytes. A comparative study of monoclonal antibodies for diagnostic purposes

The authors investigated the phenotype of "monocyte-derived histiocytes/macrophages" on frozen sections of various human tissues, in 12 histiocytic tumors, and in 15 large cell non-Hodgkin's lymphomas. The monoclonal antibodies (MAbs) considered specifically directed against antigens associated with monocytes/histiocytes included the following: Leu-M1, Leu-M3, Leu-M5, My4, My7, My8, My9, anti-Monocyte 1, anti-Monocyte 2, RFD-7, RFD-9, OKM1, and FMC17. The histiocytes in normal tissues and the tumor cells of the histiocytic malignancies expressed these antigens in various degrees. They were not reactive with MAbs specific for lymphocytes, myeloid cells, or Reed-Sternberg cells (Ki-1 antigen). Out of these 13 MAbs, only the labeling by MAb Leu-M3, Leu-M5, anti-Monocyte 1, and RFD-7 was restricted to normal and malignant monocytes/histiocytes. In combination with their broad labeling of different types of monocytes/macrophages, these MAbs are of value in differential diagnostic purposes to distinguish histiocytic malignancies from large cell lymphomas. However, none of the 13 MAbs can be considered as pan-histiocytic reagents because they did not recognize all cell types belonging to the mononuclear/phagocytic system.     

Discordant expression of CD3 and T-cell receptor beta-chain antigens in T-lineage lymphomas.

Using an immunoperoxidase technique that identifies both surface and cytoplasmic antigen expression, the authors examined 28 benign reactive lymphorproliferative lesions and 55 T-lineage lymphomas for reactivity with CD3 (Leu-4; T-cell receptor-associated antigen) and beta F1 antibodies, the latter recognizing nonpolymorphic determinants on T-cell receptor beta chains. Consistent with previous observations that these two antigens are co-expressed on the vast majority of thymocytes, peripheral blood T cells and tonsillar T cells, all 28 reactive lymphoproliferations showed essentially identical patterns of CD3 and beta F1 expression. In contrast, only 29 of 55 T-lineage lymphomas displayed coexpression of these antigens. Among 33 peripheral T-cell lymphomas, 11 cases showed CD3/beta F1 discordance (7 CD3+/beta F1-; 4 CD3-/beta F1+), and 5 showed absence of both these antigens. Nine of 22 T-lymphoblastic lymphomas showed CD3/beta F1 discordance (all CD3+/beta F1-), and 1 case was CD3-/beta F1-. These patterns of CD3/beta F1 expression, along with the patterns of CD2, CD4, CD5, CD7, and CD8 antigen expression in these neoplasms, indicate that T-cell lymphomas can manifest phenotypes not apparently reflective of normal T populations and suggest the presence of abnormal gene expression in these malignancies. The existence of aberrant phenotypes in T-cell neoplasia suggests caution in interpretation of investigations using T-lineage malignancies as models of normal T-cell biology. Finally, the identification of phenotypic abnormalities in T-lineage populations can be of great diagnostic usefulness in the delineation of benign versus malignant T-cell proliferations.     

Immunohistochemistry of markers of histiomonocytic cells in malignant fibrous histiocytomas. A monoclonal antibody study

Nine cases of malignant fibrous histiocytomas (MFH) were examined immunohistochemically in frozen sections with six different monoclonal antibodies to histiomonocytic and related cells (EBM11, HAM-56, KB90, antibodies to dendritic reticulum cells, HLADR and LCA). Ten other soft tissue sarcomas, two desmoid tumors, twelve carcinomas, three seminomas and four lymphomas were studied for comparison. All cases of MFH showed positivity for histiomonocytic cell antigens. In six cases, the positive cells could be clearly interpreted to be infiltrating non-neoplastic cells. However, immunoreactivity for multiple histiocytic markers (EBM11, HAM-56, KB90, HLADR) was seen in tumor cells in three cases of MFH. In one of these cases, the positivity could be verified with KP1, an antibody to histiomonocytic cells applied in formalin fixed and paraffin embedded tissue. None of the tumors was positive with the antibody to dendritic reticulum cells or LCA. In the series of non-histiocytic tumors, no cases showed widespread positivity for multiple histiocytic markers. Our results suggest that in relation to true histiomonocytic differentiation MFH might be a heterogeneous group of tumors. The widespread immunoreactivity for multiple histiocytic markers in some cases may indicate a true histiomonocytic differentiation in some MFHs.     

Enzyme histochemical observation of fibrohistiocytic tumors

The reactivity of lysosomal enzymes in 17 fibrohistiocytic tumors were examined histochemically to evaluate the histiocytic nature of the tumors. The lysosomal enzymes examined were acid phosphatase (Ac-P), non-specific esterase (NS-E), beta-glucuronidase (beta-GL), and N-acetyl-beta-glucosaminidase (N-GA). The tumors examined were eight malignant fibrous histiocytomas (MFH) (i.e., five common types, two myxoid types, and one inflammatory type), one atypical fibroxanthoma of the skin (AFX), one dermatofibrosarcoma protuberans (DFSP), two giant cell tumors of the tendon sheath (GCT), and five dermatofibromas (DF). Seven of 8 MFH showed strong reactivity for all enzymes examined. Positive reactions were seen as evenly distributed granules in the cytoplasm of fibroblastic, histiocytic and giant cells in all types of the tumors. Almost all AFX, GCT, and DF showed moderate to strong reactivity. These findings suggest that these tumors were composed of cells with the enzymatic character of histiocytes. However, DFSP contained no cells giving a positive reaction, and thus its histiocytic nature could not demonstrated.     

Small bowel transplantation in a child. Morphologic, immunohistochemical, and clinical results

A small bowel transplant was performed on a five-year-old boy with a short bowel syndrome. The donor was the child's mother. Despite immunosuppressive therapy, the transplant was acutely rejected and had to be explanted on the twelfth day. Morphologic and immunohistochemical investigations on subsequent biopsies taken from the small bowel transplant were carried out. Besides typical changes in epithelial cells and the presence of T-cell infiltrates and Ig-deposits in vessels, many macrophages were seen. The submucosa in particular was invaded before rejection by numerous macrophages with positive results of antimonocyte/macrophage antibodies Ki-M6 and Ki-M7. The number of the macrophage antibodies Ki-M6 and Ki-M7. The number of the monocyte/macrophage cells and the immunohistochemical characteristics of the same may be important parameters for monitoring small bowel transplantations.     

Immunohistochemical investigations of tumors of supposed fibroblastic-histiocytic origin

The aim of this study was to localize alpha 1-antitrypsin, ferritin, and lysozyme by means of the indirect immunoperoxidase technique and to evaluate the significance of these antigens as markers of histiocytic differentiation in tumors of a supposed dual fibroblastic-histiocytic origin. The series comprised 31 malignant fibrous histiocytomas (MFH) of the pleomorphic, spindle cell, and myxoid types, four cutaneous fibrous histiocytomas, and four atypical fibroxanthomas, four dermatofibrosarcoma protuberans, and two osteoclastomas of bone. For comparison, 15 soft tissue sarcomas of various other types were examined. Of the MFHs of the pleomorphic type, 18 of 22 (82 per cent) were positively stained for alpha 1-antitrypsin and 12 of 22 (54 per cent) were positively stained for ferritin. Of the five MFHs of the spindle cell type, none was positively stained for alpha 1-antitrypsin, three were positive for ferritin, and one was positive for lysozyme. None of the myxoid variants (corresponding to grade I-II myxofibrosarcoma) was positively stained for either of the antigens. These results and the observations made on the cutaneous fibrous histiocytomas, atypical fibroxanthomas, dermatofibrosarcoma protuberans, and the various soft tissue sarcomas indicated that 1) alpha 1-antitrypsin is a valuable marker of histiocytic differentiation in both benign and malignant fibrous histiocytomas, 2) ferritin can be visualized in more than half of these fibroblastic-histiocytic tumors, and the presence of ferritin distinguishes the spindle cells of these tumors from fibroblasts of connective tissue and most fibrosarcomas, and 3) lysozyme, although a good marker of histiocytic differentiation in ordinary histiocytes and benign fibrous histiocytomas, is a poor marker of neoplastic histiocytes of malignant tumors. The results further support the concept that MFH is a tumor of a dual fibroblastic-histiocytic origin.     

Ultrastructural Heterogeneity in Malignant Fibrous Histiocytoma of Soft Tissue

Five soft tissue sarcomas with histological features of malignant fibrous histiocytoma were selected to illustrate their ultrastructural heterogeneity. One case displayed the mixture of fibroblastic and histiocytic cells characteristic of the majority of malignant fibrous histiocytomas. In 1 case the tumor was composed entirely of primitive mesenchymal cells. The other 3 cases showed lipogenic, neurogenic, and “granular-cell” differentiation, respectively. These findings emphasize the important role of electron microscopy in the precise diagnosis and classification of malignant fibrous histiocytoma.     

Ultrastructural Heterogeneity in Malignant Fibrous Histiocytoma of Soft Tissue

Five soft tissue sarcomas with histological features of malignant fibrous histiocytoma were selected to illustrate their ultrastructural heterogeneity. One case displayed the mixture of fibroblastic and histiocytic cells characteristic of the majority of malignant fibrous histiocytomas. In 1 case the tumor was composed entirely of primitive mesenchymal cells. The other 3 cases showed lipogenic, neurogenic, and “granular-cell” differentiation, respectively. These findings emphasize the important role of electron microscopy in the precise diagnosis and classification of malignant fibrous histiocytoma.     

Malignant schwannoma with the microscopic features of a malignant fibrous histiocytoma

A case of malignant schwannoma is described in which the primary tumor showed morphologic signs of malignant fibrous histiocytoma, but these were not confirmed by immunohistochemical assays which were negative for markers of histiocytic tumors such as alpha 1-antitrypsin and alpha 1-antichymotrypsin. In the recurring tumor, typical palisade structures were found. Difficulties attending the diagnostic differentiation of these two tumors are discussed. It is concluded that histogenetic characteristics of malignant fibrous histiocytomas must be known to be able to establish more precise criteria on which the differentiation may be based.     

Malignant fibrous histiocytoma. Expression of monocyte/macrophage differentiation antigens detected with monoclonal antibodies.

Monoclonal antibodies were used in an investigation of the histogenesis of malignant fibrous histiocytoma (MFH), a neoplasm with morphologic features of both fibroblastic and histiocytic differentiation. In 4 cases of MFH studied, the tumor cells were found to react uniformly with antibodies to determinants expressed on monocyte macrophages (T-200, Ia, MoS-1, MoS-39, MoR-17). Both spindle and histiocyte-like tumor cells expressed these markers. In contrast, in 8 non-MFH soft tissue tumors, tumor cell reactivity was not observed. The reactivity of the spindle cells of MFH for determinants of monocyte/macrophages favors their origin from tissue histiocytes (facultative fibroblasts). The results support the view that MFH is a tumor of the mononuclear phagocyte system.