Immunohistochemical characterization of Ki-M6 monoclonal antibody in Bouin-fixed,paraffin-embedded sections of normal and neoplastic human tissues

Summary A monoclonal antibody (Ki-M6) against the CD 68 antigen, which labels cells of the monocyte/macrophage system, was tested on Bouin-fixed, paraffin-embedded samples of normal, reactive and neoplastic tissues by an avidin-biotin-peroxidase complex method, with the aim of establishing its value in diagnostic pathology. In normal human tissues, Ki-M6 reactivity was confined to the so-called resident macrophages populating normal organs under physiological conditions. Moreover, restricted reactivity against cells of macrophage lineage was observed in reactive and inflammatory lesions. Granulocytes, monocyte/macrophage-related immune accessory cells, and other analysed normal tissue structures did not reveal any reactivity. Ki-M6 was strongly reactive with the cases of benign (4/4) and malignant (15/15) fibrous histiocytomas, in addition to the true histiocytic lymphomas (3/3). Cases of granular cell tumour (2/3) showed strong reactivity with Ki-M6, whereas only few immunoreactive cells, with weak staining, were seen in the other Ki-M6-positive neoplasms [neurofibroma (3/3), benign schwannoma (1/2), ganglioneuroma (1/1), malignant schwannoma (5/9), melanoma (9/28), dermatofibrosarcoma protuberans (1/1), myelomonocytic leukaemia (3/3)]. Among the epithelial malignancies tested (47 cases), Ki-M6 was positive only in renal cell carcinoma (11/14). Malignant lymphomas of the Hodgkin (56 cases) and non-Hodgkin type (67 cases) were uniformly non-reactive. From these data, Ki-M6 appears to be an excellent marker of monocyte/macrophage-related cells and appears to be a reliable indicator for fibrous histiocytomas and true histiocytic malignancies. The availability of this additional antibody capable of staining routinely processed tissue is of practical interest.     

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).     

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.     

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.     

Demonstration of S-100 protein distribution in human lymphoid tissues by the avidin-biotin complex immunostaining method

Immunoreactivity for S-100 protein was investigated immunohistochemically in a series of 49 fixed and paraffin-embedded normal, reactive, and neoplastic human lymphoid tissue specimens. The avidin-biotin complex immunoperoxidase method was used, with overnight (12-hour) incubation with a commercially available antiserum to S-100 protein. In addition, cryostat sections were tested with DRC 1 monoclonal antibody to dendritic reticulum cells (DRCs) in three cases and with OKT6 antibody to interdigitating reticulum cells (IRCs) in nine cases. All tissues, including lymph nodes, tonsils, adenoid, spleens, appendices, thymuses, and tissues containing nodular reactive lymphoid infiltrates, demonstrated a consistent immune staining pattern. A striking network composed of dendritic processes that showed finely granular S-100 protein immunoreactivity was observed in most of the follicular germinal centers; a similar dendritic pattern was observed in the follicular centers when the corresponding frozen sections were immunostained with DRC 1. In the extrafollicular areas, the S-100-positive cells topographically and morphologically resembled the IRCs that were demonstrated by OKT6 antibody in the corresponding frozen sections. The results seem to indicate that cells topographically and morphologically similar to IRCs and DRCs in human lymphoid tissues from different sites share immunoreactivity for S-100 protein. The present study confirms the unexpected presence of S-100 protein in dendritic cells of follicular germinal centers by a simple and currently available method.     

Detection of a monocyte/macrophage differentiation antigen in routinely processed paraffin-embedded tissues by monoclonal antibody Ki-M1P

A new monoclonal antibody Ki-M1P that is raised against supernatants of detergent solubilized human lymph node tissue is described. Ki-M1P recognizes in particular monocytes and their macrophage derivatives as tested by light- and electron-microscopic immunohistochemistry. Granulocytes, dendritic cells as the accessory cells of humoral and cellular immune response, and epithelial, endothelial, neural, and mesenchymal cells do not react with Ki-M1P. In extensive application Ki-M1P has proven to be a useful marker for distinguishing monocytic leukemias within FAB groups M4 and M5. The recognized antigen is composed of five proteins with molecular masses of about 60, 92, 98, 124, and 150 kDa in blood monocytes, whereas tissue macrophages tested so far expressed only the 60-kDa protein. Because the Ki-M1P antigen is not destroyed or masked during routine fixation and paraffin embedding of biopsy tissue samples, Ki-M1P represents a useful diagnostic reagent for the identification of physiological functional and pathologic reaction forms as well as neoplastic variants of the human monocyte/macrophage system even in retrospective studies.     

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.     

Vimentin immunostaining in fibroblastic reticulum cells within human reactive and neoplastic lymphoid follicles

We analyzed the distribution of fibroblastic reticulum cells (FRCs), stationary cells of lymphoid tissues, as visualized by the anti-vimentin (V9) monoclonal antibody in human reactive and neoplastic lymphoid follicles, by using immunoenzymatic and immunofluorescence methods on fixed and paraffin-embedded tissue sections from 37 lymphoid specimens with reactive disorders and 10 specimens with nodular/follicular non-Hodgkin's lymphomas (NHLs). The pattern of distribution of the vimentin-positive (VIM+) FRCs was compared with that of follicular dendritic reticulum cells (DRCs) as visualized by anti-S-100 protein antibody. Elongate VIM+ FRCs intimately attached to reticulum fibers were randomly distributed in the paracortical and interfollicular areas of lymph nodes, whereas they were recognized specifically in the mantle zones of the secondary follicles, mostly in the outer margins. Germinal centers were consistently devoid of VIM+ FRCs. Comparative analysis on serial sections as well as paired immunoperoxidase and double immunofluorescence studies demonstrated that there was a sharp difference between the patterns of intrafollicular distribution of VIM+ FRCs and S-100 protein-positive (S-100+) DRCs without juxtaposition, the FRCs being confined to the mantle zones. In the 10 nodular/follicular NHLs VIM+ FRCs could be observed in the thinned mantles of neoplastic nodules displaying a corona-like pattern that accentuated the boundaries of the nodules. The results of this study support the view that the intrafollicular distribution of VIM+ FRCs is specific for the mantle zone. The different microenvironmental organization within the follicles of VIM+ FRCs and S-100+ DRCs suggests that FRCs or at least VIM+ FRCs are stationary cells strictly related to the mantle zone microenvironment, where they may play a role in supposed sustentacular and immunologic functions similar to that of DRCs in the germinal center microenvironment.     

Equine macrophage identification with an antibody (Ki-M6) to human CD68 and a new monoclonal antibody (JB10)

Monoclonal antibodies (mAbs) recognizing equine macrophages are scarce. The present study compared the immunocytochemical staining of various equine tissues (lymphoid tissue, lung, liver, small intestine, skin and blood leucocytes) by an antibody, Ki-M6, which detects CD68 in human macrophages and dendritic cells, and by a new anti-equine mAb, JB10, with staining produced by two previously described anti-equine macrophage mAbs, CZ2.2 and CZ3.3. Ki-M6 was shown to identify equine macrophages, which had a distribution different from those identified by CZ2.2 and CZ3.3. JB10 identified equine macrophages with a distribution similar to those identified by Ki-M6, but additionally bound to polymorphonuclear leucocytes. Flow cytometry of peripheral blood leucocyte subpopulations and tissue immunocytochemistry were used to compare staining by JB10 with that of CZ2.2 and CVS19; the latter identifies the myeloid antigen, EqCD13, found on polymorphonuclear leucocytes. The staining by JB10 differed from that of both CZ2.2 and CVS19, suggesting that JB10 detects a different molecule. These additional mAbs should prove useful for the future study of new, defined, populations of macrophages in equine immune responses and pathology, and, in the case of Ki-M6 antibody, may make possible an analysis of the structure, distribution and function of the CD68 molecule in the horse.     

Differential expression of Ca(2+)-binding proteins on follicular dendritic cells in non-neoplastic and neoplastic lymphoid follicles.

We studied the Ca(2+)-capture ability of follicular dendritic cells (FDCs) in tonsillar secondary lymphoid follicles (LFs) and the expression of six Ca(2+)-binding proteins (CBPs), caldesmon, S-100 protein, calcineurin, calbindin-D, calmodulin, and annexin VI in LFs of various lymphoid tissues and caldesmon and S-100 protein in neoplastic follicles of follicular lymphomas. First, Ca(2+)-capture cytochemistry revealed extensive Ca(2+) capture in the nuclei and cytoplasm of FDCs, but little or none in follicular lymphocytes. All six CBPs were localized immunohistochemically in the LFs and were always present in the basal light zone. Immunoelectron microscopic staining of FDCs was classified into two patterns: caldesmon was distributed in the peripheral cytoplasm like a belt; S-100 protein, calcineurin, calbindin-D, and calmodulin were distributed diffusely in the cytosol. Annexin VI was, however, negative on FDCs. Immunocytochemistry also demonstrated CBP-positive FDCs within FDC-associated clusters isolated from germinal centers. In situ hybridization revealed diffuse calmodulin mRNA expression throughout the secondary LFs. These data indicate that the CBPs examined may regulate Ca(2+) in the different subcellular sites of FDCs, and the roles of CBPs may be heterogeneous. We also investigated the distribution of caldesmon and S-100 protein in follicular lymphomas on paraffin-embedded tissue sections. FDCs within grades I and II neoplastic follicles clearly expressed caldesmon, but not S-100 protein, except a part of grade II neoplastic follicles. FDCs within grade III follicles showed no caldesmon, but frequently expressed S-100 protein. These results demonstrate that the caldesmon and S-100 protein staining patterns of grade I follicular lymphomas are different from those of grade III follicular lymphomas and suggest that FDC networks in grade I neoplastic follicles may be similar to those in the light zone within non-neoplastic follicles, FDC networks in grade III neoplastic follicles may be similar to those in dark and basal light zones within non-neoplastic follicles, and grade II follicles may be intermediate between grade I and grade III follicles.     

Natural killer (Leu 7+) cells in reactive lymphoid tissues and malignant lymphomas

Leu 7 (HNK-1) is a monoclonal antibody reported to identify human natural killer/killer cells. The frequency and distribution of Leu 7+ cells in 14 reactive lymphoid tissues and 47 malignant lymphomas were studied using the frozen section immunoperoxidase technic. In reactive lymphoid tissues, Leu 7+ cells were concentrated in the pale zone of germinal centers and usually were relatively scarce in the interfollicular areas. Of the malignant lymphomas, follicular lymphomas most consistently had numerous admixed Leu 7+ cells and lymphoblastic lymphomas the least. The authors' findings suggest that Leu 7+ cell accumulation in normal and neoplastic lymphoid tissue is associated at least in part with something shared by the pale zone of the normal germinal centers and the presence of neoplastic germinal centers. This association does not appear to be a simple response to lymphoid proliferation.     

CNA.42, a new monoclonal antibody directed against a fixative-resistant antigen of follicular dendritic reticulum cells.

A new monoclonal antibody (MAb), CNA.42, was generated using the CEM T-cell line. It recognizes a 120-kd formalin-resistant glycosylated antigen that is mainly expressed by follicular dendritic reticulum cells (FDRCs). This antigen is also expressed by a few mononuclear cells in the paracortical area of reactive lymph nodes and by some cortical thymocytes. Two hundred and eighty-nine cases of hematopoietic tumors of various types were tested with this antibody. They showed either intact FDRC networks or FDRC networks dispersed among malignant cells. In follicular lymphomas, the follicular pattern was highlighted by CNA.42 MAb. Expanded FDRC networks were found in angioimmunoblastic T-cell lymphomas. Neoplastic cells were positive in 43.6% (24/55) of T-cell and 4.6% (6/129) of B-cell lymphomas. The highest percentage of cases with positive neoplastic cells was found in anaplastic large-cell lymphomas (62.5%; 15/24). In Hodgkin's disease, FDRC networks, sometimes encasing Hodgkin and Reed-Sternberg (HRS) cells, were found. HRS cells were also stained by this antibody in 23 (21.9%) of the 105 cases examined. A variety of normal nonlymphoid tissues and nonhematopoietic tumors, such as some neurogenic tumors, carcinoma, and occasional sarcomas, were found to be positive. Analysis of the reactivity of CNA.42 antibody with FDRCs of lymphoid tissue from different animal species showed similar reactivity to that observed in humans, suggesting widespread evolutionary conservation of the antigen recognized by this antibody. In daily diagnostic practice, CNA.42 MAb seems to be a suitable FDRC marker and possibly has an auxiliary role in recognizing T-cell lymphomas.     

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.     

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.     

Distribution of T-cell subsets in follicular and diffuse lymphomas of B-cell type.

The authors examined the number and distribution of cells reacting with monoclonal antibodies to T-cell subsets in frozen tissue sections of B-cell lymphomas (30 follicular and 17 diffuse lymphomas). In five diffuse lymphomas (two lymphocytic, three small cleaved cell) the neoplastic B-lymphocytes reacted with the monoclonal antibody anti-T1. In all other cases, the monoclonal antibodies to T-cell subsets reacted only with small lymphocytes concentrated between the follicles of follicular lymphomas and distributed randomly in diffuse lymphomas. The distribution of T cells and the T4+/T8+ ratio in follicular small cleaved and mixed lymphomas was similar, although not identical, to that seen in hyperplastic lymphoid follicles. Fewer T cells and a decrease in the T4+/T8+ ratio were seen in follicular large cell lymphoma and in diffuse large cell lymphomas. The number and distribution of T cells in follicular lymphomas is consistent with the hypothesis that there is a functional interaction between neoplastic B cells and benign T cells. No tumors were found in which the neoplastic B cells reacted with anti-T3, anti-T4, or anti-T8.     

VS38: a new monoclonal antibody for detecting plasma cell differentiation in routine sections.

AIMS--To characterise a new mouse monoclonal antibody, VS38, which recognises an intracytoplasmic antigen of 64 kilodaltons present in normal and neoplastic plasma cells; and to establish its value as a diagnostic reagent for routine pathological practice. METHODS--A range of normal and neoplastic tissue sections, both frozen and routinely fixed, were immunostained, using the microwave method of antigen retrieval for routinely fixed specimens. The antibody was also tested on blood and bone marrow specimens and a range of human cell lines. The molecular weight of the antigen recognised by the antibody was obtained by western blot analysis. FACS analysis was used to demonstrate the cellular location of the antigen and its presence on tonsil cell suspensions and myeloma cases. RESULTS--VS38 recognised normal and neoplastic plasma cells in all of the tissues, including all routinely fixed plasma cell neoplasms tested. The antibody also weakly stained epithelial elements within the tissue but was absent from haemopoietic cells of other lineages. CONCLUSION--Antibody VS38 is of potential value in identifying myeloma or plasmacytoma in bone marrow or other tissues. It differentiates lymphoplasmacytoid lymphoma from lymphocytic and follicular lymphoma. It also subdivides large cell lymphomas into two groups which may be a more reliable method of separating these tumours than morphology alone.     

Utilization of monoclonal antibody L26 in the identification and confirmation of B-cell lymphomas. A sensitive and specific marker applicable to formalin-and B5-fixed, paraffin-embedded tissues.

Immunophenotypic analysis of paraffin-embedded tissues of lymphoproliferative disorders has been facilitated by recent developments of monoclonal antibodies that react with epitopes that survive histologic processing. Leukocyte common antigen (LCA) antibody has made a significant contribution to the immunocytochemical separation of non-Hodgkin's lymphomas from nonlymphoid neoplasms. However, a small percentage of lymphomas, particularly some large cell or immunoblastic B-cell tumors, will not label with LCA antibody. Other antibodies, directed against B lymphocytes, experience problems of specificity and a lack of sensitivity when applied to formalin-fixed specimens. The authors recently investigated a monoclonal antibody (L26) that demonstrates excellent specificity and sensitivity for B lymphocytes, and tumors derived from them, in formalin- and B5-fixed, paraffin-embedded tissue. The avidin-biotin peroxidase complex (ABC) technique was utilized for immunostaining 95 cases of malignant lymphoproliferative disorders and a variety of normal and neoplastic nonlymphoid tissues. When applied to sections of benign lymphoid tissue, the L26 antibody labeled germinal center cells, mantle zone and scattered interfollicular lymphocytes, but not histiocytes or plasma cells. L26 marked 100% (44/44) of the large cell and immunoblastic B-cell lymphomas, along with 1 case of pre-B cell lymphoblastic lymphoma. This included 8 cases that were LCA-negative. None of the T-cell lymphomas or plasma cell tumors studied demonstrated L26 immunostaining. No normal, benign, or neoplastic nonlymphoid tissues examined stained with this antibody. L26 successfully labels B lymphocytes and B-cell lymphomas in routinely processed tissues, often with greater sensitivity and intensity than LCA. This antibody should prove invaluable in the investigation of atypical lymphoid proliferations and the identification of B-cell derived lymphomas, when fresh or frozen tissue is unavailable for analysis.     

Selective recognition of rat follicular dendritic cells (dendritic reticulum cells) by a new monoclonal antibody Ki-M4R in vitro and in vivo

Using unstimulated rat peritoneal cells as immunogen a new monoclonal antibody Ki-M4R was produced. Ki-M4R recognizes follicular dendritic cells (dendritic reticulum cells) in germinal centers of lymphoid follicles in lymphatic tissue. In addition, sinus lining cells, endothelia of postcapillary venules, as well as mesangial cells of the renal glomerula immunoreact with Ki-M4R in vitro as well as in vivo. This antibody might be useful for studying the interaction of follicular dendritic cells and B-cell immune response.     

AM-3K,A NOVEL MONOCLONAL ANTIBODY SPECIFIC FOR TISSUE MACROPHAGES AND ITS APPLICATION TO PATHOLOGICAL INVESTIGATION

An anti-human macrophage monoclonal antibody, AM-3K, was produced using human alveolar macrophages as antigen. The molecular weights of the antigen recognized by AM-3K were 120 and 70 kD. Immunohistochemically, AM-3K reacted intensely with most macrophages in lymphoreticular organs and in many other organs and tissues. In the spleen, AM-3K reacted with red pulp macrophages, some white pulp macrophages, and tingible body macrophages in lymphoid follicles. In the lymph nodes, many macrophages distributed in the outer cortex, paracortical area, medulla, capsule, or within lymphoid follicles showed an intense reaction for AM-3K. Kupffer cells of the liver, macrophages in the connective tissues, and interstitial macrophages of the kidneys, pancreas, testis, and many other organs were also strongly labelled. AM-3K also reacted with macrophages in many pathological conditions. This antibody, however, did not react with dendritic cell populations, such as epidermal Langerhans cells, interdigitating cells in the paracortex of the lymph nodes, and follicular dendritic cells within the lymphoid follicles, nor with cells other than macrophages, including epithelial cells, vascular endothelial cells, lymphocytes, and granulocytes. Reaction products for AM-3K were found on the cytoplasmic membrane of macrophages by immunoelectron microscopy. In both cryostat sections and formalin-fixed paraffin sections, this monoclonal antibody recognized the antigen present on the cell surface membrane of tissue macrophages, but not monocytes or dendritic cells.     

Aberrant MT2 positivity distinguishes follicular lymphoma from reactive follicular hyperplasia in B5- and formalin-fixed paraffin sections.

Often, it is difficult to distinguish follicular lymphoma from reactive follicular hyperplasia histologically. Immunotypic evidence of monoclonality cannot be demonstrated routinely or reliably in routine paraffin-embedded sections. To determine whether a panel of monoclonal antibodies reactive with lymphoid cells in paraffin-embedded sections might be useful in distinguishing these confusing proliferations, the authors examined 45 follicular lymphomas and 30 follicular hyperplasia with the following antibodies; L26, B2, MT1, MT2, and UCHL-I. All sections were routine paraffin preparations from formalin- or B5-fixed tissue and were immunostained with the avidin-biotin immunoperoxidase technique. Ninety-two percent of the B5-fixed and 77% of the formalin-fixed lymphomas were MT2 positive. None of the reactive hyperplasias stained positively, and none of the other antibodies demonstrated consistent differences between these benign and malignant proliferations. MT2 marks interfollicular T cells and mantle-zone B cells in normal lymph nodes but does not mark normal germinal centers; this staining pattern is retained in reactive hyperplasia. However, paradoxically, in most follicular lymphomas the neoplastic germinal centers show aberrant MT2 positively. The authors conclude that MT2 may be useful in distinguishing follicular lymphoma from follicular hyperplasia in paraffin sections.