Podoplanin (D2-40) is a Highly Effective Marker of Follicular Dendritic Cells

Cytological diagnosis of follicular dendritic cell sarcoma with a unique pattern of D2-40 immunoexpression

Fine needle aspiration procedure is routinely used for cytological diagnosis of nodal or extra nodal lesions. Follicular dendritic cell sarcoma (FDCS) is a rare mesenchymal neoplasm arising from follicular dendritic cells of lymphoid follicles at nodal and extranodal sites. Multimodal therapies have emerged for FDCS, necessitating its accurate pathologic diagnosis with additional ancillary testing for directing clinical management. By immunohistochemical analysis, FDCS is positive for the complement receptors CD21, CD23, and CD35. In addition, D2-40 is reported to be highly sensitive for FDCS with a strong membranous pattern of expression. In this study, we present the cytological diagnosis of a case of FDCS in retroperitoneal lymph nodes with an emphasis on a unique staining pattern of D2-40 which showed a strong nuclear pattern in tumor cells comparable to the membranous pattern of D2-40 on the control tissue and other surgical cases of FDCS in our comparative study.

Graph Fourier transform for spatial omics representation and analyses of complex organs

Spatial omics technologies decipher functional components of complex organs at cellular and subcellular resolutions. We introduce Spatial Graph Fourier Transform (SpaGFT) and apply graph signal processing to a wide range of spatial omics profiling platforms to generate their interpretable representations. This representation supports spatially variable gene identification and improves gene expression imputation, outperforming existing tools in analyzing human and mouse spatial transcriptomics data. SpaGFT can identify immunological regions for B cell maturation in human lymph nodes Visium data and characterize variations in secondary follicles using in-house human tonsil CODEX data. Furthermore, it can be integrated seamlessly into other machine learning frameworks, enhancing accuracy in spatial domain identification, cell type annotation, and subcellular feature inference by up to 40%. Notably, SpaGFT detects rare subcellular organelles, such as Cajal bodies and Set1/COMPASS complexes, in high-resolution spatial proteomics data. This approach provides an explainable graph representation method for exploring tissue biology and function.

Epstein-barr virus (EBV)-positive inflammatory pseudotumor-like follicular dendritic cell sarcoma (IPT-like FDCS) presenting as thrombocytopenia: A case report and literature review

Background

Follicular dendritic cell sarcoma (FDCS) represents an exceedingly rare malignant neoplasm. Inflammatory pseudotumor-like follicular dendritic cell sarcoma (IPT-like FDCS) is recognized as a variant manifestation of FDCS. The clinical incidence of this particular disease is remarkably low, resulting in the absence of established standardized clinical protocols for its management and treatment.

Methods

Presented here is a case of primary Epstein-Barr virus (EBV)-positive splenic IPT-like FDCS, noteworthy for manifesting thrombocytopenia as its initial symptom. Our study analyzed the clinicopathologic characteristics of this case and 29 previously reported cases identified in the literature. Also, we conducted a comprehensive review of pertinent literature.

Results

We administered splenectomy to this patient and verified the diagnosis of EBV-positive IPT-like FDCS through immunohistochemical examination. Postoperatively, the patient underwent a one-year follow-up period, demonstrating no signs of recurrence. Analyzing a total of 30 cases revealed that this disease is more prevalent in female patients (F:M = 1.14:1), with a median age of 62 years. Fifteen patients were asymptomatic, and nine patients presented with abdominal discomfort or pain. All patients underwent surgical treatment. Among the cases, histopathological and immunohistochemical information was unavailable for five; however, in the remaining 25 cases, histopathology revealed a distinct inflammatory cell infiltration and spindle tumor cells arranged in sheets or fascicles. These tumor cells had vesicular chromatin and distinct nucleoli and they expressed conventional FDC markers. In situ hybridization analysis of Epstein-Barr virus-encoded small RNA (EBER) showed that all 30 cases were EBV-positive. Follow-up information showed that no patients relapsed and one (3.8 %) patient died.

Conclusion

The clinical diagnosis of EBV-positive IPT-like FDCS poses considerable challenges, necessitating a conclusive diagnosis through pathological immunohistochemical examination. EBER in situ hybridization holds significance for the definitive diagnosis of the disease. We advocate for splenectomy as the treatment of choice for limited splenic IPT-like FDCS.

Graph Fourier transform for spatial omics representation and analyses of complex organs

Spatial omics technologies are capable of deciphering detailed components of complex organs or tissue in cellular and subcellular resolution. A robust, interpretable, and unbiased representation method for spatial omics is necessary to illuminate novel investigations into biological functions, whereas a mathematical theory deficiency still exists. We present SpaGFT (Spatial Graph Fourier Transform), which provides a unique analytical feature representation of spatial omics data and elucidates molecular signatures linked to critical biological processes within tissues and cells. It outperformed existing tools in spatially variable gene prediction and gene expression imputation across human/mouse Visium data. Integrating SpaGFT representation into existing machine learning frameworks can enhance up to 40% accuracy of spatial domain identification, cell type annotation, cell-to-spot alignment, and subcellular hallmark inference. SpaGFT identified immunological regions for B cell maturation in human lymph node Visium data, characterized secondary follicle variations from in-house human tonsil CODEX data, and detected extremely rare subcellular organelles such as Cajal body and Set1/COMPASS. This new method lays the groundwork for a new theoretical model in explainable AI, advancing our understanding of tissue organization and function.

Human lymph node degeneration in the thoracic region: A morphometric and immunohistochemical analysis using surgically obtained specimens

Lymph node degeneration was examined in 539 mediastinal and intrapulmonary nodes removed from 78 patients, aged 49–82 years, without cancer metastasis. Medullary sinus hyalinization observed in 36.2% of the hilar and 38.5% of the interlobar nodes. Early and smaller lesions were eosinophilic and factor VIII-positive, whereas advanced and large lesions contained a bulky mass of collagenous fiber bundles with few slender cells positive for smooth muscle actin (SMA) and factor VIII, as well as anthracotic macrophages. Subcapsular sinus hyalinization, observed in 4.3% of hilar nodes, was detected as a thick fibrous layer (over 0.2 mm) between the surface cortex and the thickened capsule. The fibrous layer contained SMA-positive slender cells, whereas the thickened capsule contained fibers positive for elastin and factor VIII. These hyalinization lesions occupied 3.6% and 0.8% of the sectional areas of hilar and lower paratracheal nodes, respectively. Areas of early and small cortical degeneration, surrounded by fibers positive for SMA and vimentin, did not contain lymphocytes and macrophages, but contained abundant small stromal cells. Silver staining suggested that advanced cortical degeneration was composed of collagen fibrils other than type I. Fatty tissues, seen in 47.8% of hilar nodes, often extended into and replaced medullary sinus tissue. Island-like remnants of medullary sinuses in areas of fatty degeneration contained various stromal cells positive for SMA, elastin, factor VIII and/or CD34. These degenerative morphologies, however, did not correlate with either age or smoking index. The present cortical degeneration usually seemed to follow hyalinization, but both were likely to occur independently.

Follicular dendritic cell sarcoma

Follicular dendritic cells (FDC) are mesenchymal-derived dendritic cells located in B-follicles where they play a pivotal role in triggering and maintaining B-cell adaptive immune response. In 1986 Dr. Juan Rosai first reported a series of neoplasms showing features of FDC and defined it as Follicular Dendritic Cell Tumor, subsequently renamed as "sarcoma" (FDCS). In its seminal and subsequent articles Rosai and colleagues highlighted the heterogeneous microscopic appearance of FDCS and its immunohistochemical and ultrastructural features.

FDCS mostly occurs in extranodal sites (79.4% of cases) and lymph nodes (15.1%); in about 7%-10% of cases it is associated with hyaline-vascular Castleman disease. Given its significant growth pattern and cytological variability, FDCS can be confused with various neoplasms and even inflammatory processes. The diagnosis requires the use of a broad spectrum of FDC markers (e.g. CD21, CD23, CD35, clusterin, CXCL13, podoplanin), particularly considering that tumor antigen-loss is frequent. The inflammatory-pseudotumor-like (IPT-like) variant of FDCS, in addition to its peculiar histopathological and clinical features, is characterized by positivity of tumor cells for Epstein-Barr virus, representing a diagnostic requisite.

No distinctive genetic and molecular anomalies have been identified in FDCS. It often carries an aberrant clonal karyotype and chromosomal structural alterations, frequently involving onco-suppressor genes. Direct or next generation sequencing showed alterations on genes belonging to the NF-κB regulatory pathway and cell-cycle regulators. In contrast to hematopoietic-derived histiocytic and dendritic cells tumors, FDCS typically lacks mutations in genes related to the MAPK pathway.

FDCS recurs locally in 28% and metastasizes in 27% of cases. Extent of the disease, surgical resectability and histopathological features are significantly associated with the outcome. IPT-like FDCS behaves as an indolent tumor, even if it often recurs locally over years.

Complete surgical excision is the gold standard of treatment. Data on targeted therapies (e.g.: tyrosine kinase inhibitors) or immune checkpoint inhibitors are very limited and responses are variable. A better understanding of the molecular drivers of this tumor may lead to potential new therapeutic strategies.

Case Report: Composite Angioimmunoblastic T-Cell Lymphoma and Epstein-Barr Virus-Positive B-Cell Lymphoproliferative Disorder as Other Iatrogenic Immunodeficiency-Associated Lymphoproliferative Disorders

Immunosuppressants are widely used to treat patients with rheumatoid arthritis (RA), and their adverse effects have been known to cause other iatrogenic immunodeficiency-associated lymphoproliferative disorders (OIIA-LPDs). We report a patient with RA who had been treated with methotrexate (MTX) and tacrolimus (TAC) and who developed whole body lymphadenopathy. We simultaneously confirmed angioimmunoblastic T-cell lymphoma (AITL) through a right cervical lymph node biopsy and Epstein-Barr virus-positive B-cell lymphoproliferative disorder (EBV-positive B-LPD) through a bone marrow examination. After cessation of immunosuppressant therapy, both LPDs completely disappeared. Patients with AITL are occasionally reported to develop B-cell lymphoma through reactivation of the EBV, which leads to clonal expansion in the microenvironment. Immunohistochemistry results revealed that both LPD components were positive for EBV-encoded RNA. Moreover, in this patient, the plasma EBV DNA level was found to be high; therefore, EBV infection was a probable etiology. Synchronous coexistence of AITL and B-LPD as an OIIA-LPD has rarely been reported. This case report is the first to discuss the disappearance of both LPDs on withdrawal of immunosuppressants only. AITL occasionally accompany B-LPD; however, this composite lymphoma comprised AITL and B-LPD, and OIIA-LPDs should not be overlooked.

Morphological hallmarks facilitating distinction of omental milky spots and lymph nodes: an exploratory study on their discriminative capacity

BACKGROUND

Omental milky spots (OMSs) are the primary lymphoid structures of the greater omentum. However, the presence of lymph nodes (LNs) has occasionally been mentioned as well. Understanding which lymphoid structures are present is of significance, especially in gastric tumor metastasis; tumor deposits in omental LNs suggest local lymphatic spread, whereas tumor deposits in OMSs suggest peritoneal spread and hence extensive disease. Since LNs and OMSs share morphological characteristics and OMSs might be wrongly identified as LNs, reliable hallmarks facilitating easy discrimination are needed.

MATERIALS AND METHOD

A series of microscopic morphological hallmarks unique to LNs were selected as potential candidates and were assessed for their discriminative capacity: 1) capsule, 2) trabeculae, 3) subcapsular sinus, 4) afferent lymphatic vessels, 5) distinct B- and T cell regions, and 6) a layered organization with, from the outside in a capsule, cortex, paracortex, and medulla. These hallmarks were visualized by multiple staining techniques.

RESULTS

Hallmarks 1, 2 5 and 6 were shown to be the most efficient as these were consistent and discriminative. They were best visualized by Picrosirius red, smooth muscle actin and a B-cell / T-cell double staining.

CONCLUSION

The presence of a capsule, trabeculae, distinct B- and T-cell regions and a layered organization represent consistent and reliable morphological features which allow to easily distinguish LNs from OMSs, especially when applied in combination.

Podoplanin as a Predictive Marker for Identification of High-Risk Mycosis Fungoides Patients: An Immunohistochemical Study

Background

Podoplanin, an important protein, has been implicated in various cellular processes, including lymphangiogenesis. Podoplanin is a mucin-type transmembrane glycoprotein that is accepted as a novel marker of lymphatic endothelial cells.

Objectives

To study the immunohistochemical expression of podoplanin in the different stages of mycosis fungoides (MF) in comparison to control and to correlate their expression with disease severity and progression.

Materials and Methods

The study included 50 patients of MF, clinically diagnosed and assessed by World Health Organization/European Organization for Research And Treatment Of Cancer Consensus and 20 normal persons as control. Skin biopsy specimens were taken from all and examined for expression of podoplanin immunohistochemically.

Results

Significant upregulation of podoplanin expression was detected in all studied patients of MF in comparison to control group. Podoplanin expression in malignant lymphocytes and also lymph vessel density showed significant upregulation in the aggressive clinical presentations as well as the highest stages regarding TNMB staging of MF.

Conclusions

Evaluation of podoplanin expression may be taken into consideration in the future as a useful tool to identify high-risk MF patients. Furthermore, it may open new therapeutic options for the clinical management of those patients.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Perivascular Adventitial Fibroblast Specialization Accompanies T Cell Retention in the Inflamed Human Dermis

Perivascular accumulation of lymphocytes can be a prominent histopathologic feature of various human inflammatory skin diseases. Select examples include systemic sclerosis, spongiotic dermatitis, and cutaneous lupus. Although a large body of work has described various aspects of the endothelial and vascular smooth muscle layers in these diseases, the outer adventitial compartment is poorly explored. The goal of the current study was to characterize perivascular adventitial fibroblast states in inflammatory human skin diseases and relate these states to perivascular lymphocyte accumulation. In normal skin, adventitial fibroblasts are distinguished by CD90 expression, and dense perivascular lymphocytic infiltrates are uncommon. In systemic sclerosis, this compartment expands, but lymphocyte infiltrates remain sparse. In contrast, perivascular adventitial fibroblast expression of VCAM1 is upregulated in spongiotic dermatitis and lupus and is associated with a dense perivascular T cell infiltrate. VCAM1 expression marks transitioned fibroblasts that show some resemblance to the reticular stromal cells in secondary lymphoid organs. Expanded adventitial compartments with perivascular infiltrates similar to the human settings were not seen in the inflamed murine dermis. This species difference may hinder the dissection of aspects of perivascular adventitial pathology. The altered perivascular adventitial compartment and its associated reticular network form a niche for lymphocytes and appear to be fundamental in the development of an inflammatory pattern.

Corneal lymphangiogenesis facilitates ocular surface inflammation and cell trafficking in dry eye disease

PURPOSE

While the normal cornea has limited innervation by the lymphatic system, chronic immune-inflammatory disorders such as dry eye (DE) can induce lymphangiogenesis in the ocular surface. Using a conditional knock-down murine model, Lyve-1^Cre;VEGFR2^flox mice, this study investigated the role of lymphangiogenesis in the pathophysiology of DE.

METHODS

DE was induced in both wild type (WT) B6 and Lyve-1^Cre;VEGFR2^flox mice. Tissue immunostaining and volumetric gross measurements were used to assess changes in the ocular surface, skin, and lymph nodes (LNs). The expression of lymphangiogenic factors (TNF-α, IL-6/-8/-12/-17, VEGF-C/-D, IFN-γ, VEGFR-2/-3, Lyve-1, and podoplanin) and the frequency of immune cells (CD4, CD11b, and CD207) on the ocular surface and lacrimal glands were quantified by real-time polymerase chain reaction and flow cytometry.

RESULTS

Compared to WT mice, there were fewer lymphatic vessels and a reduction in lymphangiogenic markers in the ocular surface and skin of Lyve-1^Cre;VEGFR2^flox mice. After DE induction, mRNA levels of TNF-α, IL-8, and IFN-γ were significantly reduced in Lyve-1^Cre;VEGFR2^flox mice compared to WT mice (p < .01). Surprisingly, the LNs from Lyve-1^Cre;VEGFR2^flox mice with DE were significantly smaller and populated by fewer dendritic cells and effector T cells than those from WT mice (p < .001). Furthermore, immunostaining showed corneal nerves in the DE-induced Lyve-1^Cre;VEGFR2^flox mice were notably intact like in the naïve condition.

CONCLUSIONS

Inhibition of lymphangiogenesis in the cornea effectively attenuates not only the inflammatory response including trafficking of immune cells but also preserves corneal nerves under desiccating stress. Corneal lymphangiogenesis might be a contributing factor in deterioration on the ocular surface homeostasis.

Use of Smooth Muscle Myosin Heavy Chain as an Effective Marker of Follicular Dendritic Cells

Smooth muscle myosin heavy chain (SMMHC) is a major structural component of the contractile apparatus in smooth muscle cells. Even though it is considered a relatively specific marker for terminal smooth muscle cell differentiation, expression in other cell types such as follicular dendritic cells (FDCs) has rarely been reported. To determine whether SMMHC represents an effective FDC marker in lymphoid tissues, we compared the immunohistochemical results for SMMHC with those of the traditional FDC markers podoplanin (D2-40) and CD21. Paraffin sections of 44 lymphoid tissues were analyzed, including 31 cases of follicular hyperplasia, 6 cases of follicular lymphoma, 2 cases of peripheral T-cell lymphoma, 3 cases of diffuse large B-cell lymphoma arising in follicular lymphoma, 1 case of nodular sclerosis classical Hodgkin lymphoma, and 1 case of small lymphocytic lymphoma. There was no statistically significant difference between the number of SMMHC-positive and D2-40-positive or CD21 lymph nodes (P>0.05). The extent and intensity of SMMHC-positive FDCs were similar to those of D2-40-positive FDCs (P=0.127 and 0.733, respectively), but significantly lower compared with those of CD21 cells (P=0.009 and 0.00002, respectively). However, in contrast to CD21 which was also positive in some germinal center B cells, SMMHC expression was restricted to FDCs. Our results indicate that SMMHC is an excellent marker for FDCs and can be particularly helpful in demonstrating the underlying architecture in lymphoid processes.

Morphological study of tooth development in podoplanin-deficient mice

Podoplanin is a mucin-type highly O-glycosylated glycoprotein identified in several somatyic cells: podocytes, alveolar epithelial cells, lymphatic endothelial cells, lymph node stromal fibroblastic reticular cells, osteocytes, odontoblasts, mesothelial cells, glia cells, and others. It has been reported that podoplanin-RhoA interaction induces cytoskeleton relaxation and cell process stretching in fibroblastic cells and osteocytes, and that podoplanin plays a critical role in type I alveolar cell differentiation. It appears that podoplanin plays a number of different roles in contributing to cell functioning and growth by signaling. However, little is known about the functions of podoplanin in the somatic cells of the adult organism because an absence of podoplanin is lethal at birth by the respiratory failure. In this report, we investigated the tooth germ development in podoplanin-knockout mice, and the dentin formation in podoplanin-conditional knockout mice having neural crest-derived cells with deficiency in podoplanin by the Wnt1 promoter and enhancer-driven Cre recombinase: Wnt1-Cre;Pdpn^Δ/Δmice. In the Wnt1-Cre;Pdpn^Δ/Δmice, the tooth and alveolar bone showed no morphological abnormalities and grow normally, indicating that podoplanin is not critical in the development of the tooth and bone.

Altered Dermal Fibroblasts in Systemic Sclerosis Display Podoplanin and CD90

Tissue injury triggers the activation and differentiation of multiple cell types to minimize damage and initiate repair processes. In systemic sclerosis, these repair processes appear to run unchecked, leading to aberrant remodeling and fibrosis of the skin and multiple internal organs, yet the fundamental pathological defect remains unknown. We describe herein a transition wherein the abundant CD34(+) dermal fibroblasts present in healthy human skin disappear in the skin of systemic sclerosis patients, and CD34(-), podoplanin(+), and CD90(+) fibroblasts appear. This transition is limited to the upper dermis in several inflammatory skin diseases, yet in systemic sclerosis, it can occur in all regions of the dermis. In vitro, primary dermal fibroblasts readily express podoplanin in response to the inflammatory stimuli tumor necrosis factor and IL-1β. Furthermore, we show that on acute skin injury in both human and murine settings, this transition occurs quickly, consistent with a response to inflammatory signaling. Transitioned fibroblasts partially resemble the cells that form the reticular networks in organized lymphoid tissues, potentially linking two areas of fibroblast research. These results allow for the visualization and quantification of a basic stage of fibroblast differentiation in inflammatory and fibrotic diseases in the skin.

Value of podoplanin as an immunohistochemical marker in tumor diagnosis: a review and update

Podoplanin is a type I integral membrane glycoprotein that, because it is expressed in lymphatic endothelium, but not in vascular blood vessel endothelial cells, is commonly used in the identification of lymphatic endothelial differentiation in vascular endothelial neoplasms and lymphatic invasion by tumor. Because podoplanin is also expressed in mesothelial cells and fetal gonocytes, it has proved to be a useful marker for assisting in the differential diagnosis of mesotheliomas and germ cell tumors, particularly seminomas/dysgerminomas. Podoplanin expression has also been reported in a wide variety of other neoplasms, including hemangioblastomas, meningiomas, cartilaginous tumors, and follicular dendritic cell neoplasms. This article reviews the information that is currently available on the application of podoplanin immunostaining in diagnostic pathology.

Follicular Dendritic Cell Sarcoma Mediastinum - a case report

Follicular dendritic cell tumor (FDCT) are extremely rare difficult to diagnose category tumors.There has been a considerable controversy in medical community regarding precise classification and optimal management of this tumor with some treating it as a form of non Hodgkins lymphoma and some as soft tissue sarcomas.The number of published cases are still low and documentation too heterogenous to give statistically ified therapeutic recommendation of these tumors.This case report aims to highlight various aspects of diagnosing and treating this rare entity.

Podoplanin (D2-40) is a reliable marker of urinary bladder myofibroblasts (telocytes)

Podoplanin, D2-40, has been described in a variety of normal and neoplastic tissues. It is often used for highlighting lymphatics. We evaluated the expression of podoplanin in α-smooth muscle actinpositive myofibroblasts producing the suburothelial layer in tunica propria of the urinary bladder that have some similar features with telocytes. Our results showed that these cells demonstrate distinct D2-40 immunoreactivity from telocytes occurring in the renal pelvis and ureter. We observed positive reaction not only in bioptic specimens from women with interstitial cystitis, but also in a control group of women and men treated for pathological bladder lesion different from interstitial cystitis. It is interesting that identical staining reaction was observed in the ureters only exceptionally. In addition, we examined samples from myofibroblastic tumoriform lesions of soft tissue such as nodular fascitis and fibromatosis (desmoid) and we obtained negative results. It means that the so-called myofibroblasts of urinary bladder tunica propria have a unique immunophenotype that has probably not been described until now. Our findings suggest that D2-40 can be used as a complementary immunostainer to α-smooth muscle actin on urinary bladder biopsies from patients with interstitial cystitis. The role of D2-40 as an immunohistochemical marker is still being investigated.

Distribution of podoplanin-expressing cells in the mouse nervous systems

Podoplanin is a mucin-type glycoprotein which was first identified in podocytes. Recently, podoplanin has been successively reported as a marker for brain and peripheral nerve tumors, however, the distribution of podoplanin-expressing cells in normal nerves has not been fully investigated. This study aims to examine the podoplanin-expressing cell distribution in the mouse head and nervous systems. An immunohistochemical study showed that the podoplanin-positive areas in the mouse peripheral nerve and spinal cord are perineurial fibroblasts, satellite cells in the dorsal root ganglion, glia cells in the ventral and dorsal horns, and schwann cells in the ventral and dorsal roots; in the cranial meninges the dura mater, arachnoid, and pia mater; in the eye the optic nerve, retinal pigment epithelium, chorioidea, sclera, iris, lens epithelium, corneal epithelium, and conjunctival epithelium. In the mouse brain choroid plexus and ependyma were podoplanin-positive, and there were podoplanin-expressing brain parenchymal cells in the nuclei and cortex. The podoplanin-expressing cells were astrocyte marker GFAP-positive and there were no differences in the double positive cell distribution of several portions in the brain parenchyma except for the fornix. The results suggest that podoplanin may play a common role in nervous system support cells and eye constituents.

Lymphoid aggregates that resemble tertiary lymphoid organs define a specific pathological subset in metal-on-metal hip replacements

Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) has been used to describe the histological lesion associated with metal-on-metal (M-M) bearings. We tested the hypothesis that the lymphoid aggregates, associated with ALVAL lesions resemble tertiary lymphoid organs (TLOs). Histopathological changes were examined in the periprosthetic tissue of 62 M-M hip replacements requiring revision surgery, with particular emphasis on the characteristics and pattern of the lymphocytic infiltrate. Immunofluorescence and immunohistochemistry were used to study the classical features of TLOs in cases where large organized lymphoid follicles were present. Synchrotron X-ray fluorescence (XRF) measurements were undertaken to detect localisation of implant derived ions/particles within the samples. Based on type of lymphocytic infiltrates, three different categories were recognised; diffuse aggregates (51%), T cell aggregates (20%), and organised lymphoid aggregates (29%). Further investigation of tissues with organised lymphoid aggregates showed that these tissues recapitulate many of the features of TLOs with T cells and B cells organised into discrete areas, the presence of follicular dendritic cells, acquisition of high endothelial venule like phenotype by blood vessels, expression of lymphoid chemokines and the presence of plasma cells. Co-localisation of implant-derived metals with lymphoid aggregates was observed. These findings suggest that in addition to the well described general foreign body reaction mediated by macrophages and a T cell mediated type IV hypersensitivity response, an under-recognized immunological reaction to metal wear debris involving B cells and the formation of tertiary lymphoid organs occurs in a distinct subset of patients with M-M implants.

Frequent expression of follicular dendritic cell markers in Hodgkin lymphoma and anaplastic large cell lymphoma

AIMS

Although the tumour cells of Hodgkin lymphoma (HL) are derived from mature B-cells, the lineage infidelity of Hodgkin/Reed-Sternberg cells (HRSs) often causes diagnostic problems. Recently introduced HRS markers are also positive for follicular dendritic cells (FDCs). We investigated the expression of several FDC markers in HL and anaplastic large cell lymphoma (ALCL) and evaluated their diagnostic efficacy.

METHODS

Eighty-five cases of HL and 52 cases of ALCL were included in this study. Immunohistochemistry was performed for glioma-associated homologue (GLI) 3, class III β-tubulin (TUBB3), fascin, clusterin, γ-synuclein, podoplanin, syntenin, CD21, CD35 and EGFR.

RESULTS

HRSs were diffusely positive for GLI3, fascin and TUBB3; the mean positivity rates per case were 94% for GLI3, 82% for fascin, 69% for TUBB3, 17% for clusterin, 17% for γ-synuclein and 14% for syntenin. Podoplanin, CD21, CD35 and EGFR were almost negative. However, the frequency of marker expression was not associated with the histologic subtype or the presence of Epstein-Barr virus (EBV). ALCL showed a similar pattern to HL, but the overall frequency of positivity was lower than that observed in HL. The mean positivity rates were 56% for GLI3, 62% for fascin, 58% for TUBB3 and 21% for clusterin. The other markers were nearly negative. Anaplastic large cell lymphoma kinase positivity did not affect the expression rates.

CONCLUSIONS

This study confirmed the frequent expression of FDC markers in HL and ALCL. Especially, GLI3, fascin and TUBB3 are the most sensitive markers. Further studies are required to evaluate the association between FDCs, HRSs and ALCL cells.

Immunohistochemical Examination of Novel Rat Monoclonal Antibodies against Mouse and Human Podoplanin

This study aims to develop new monoclonal antibodies (mAbs) against mouse and human podoplanin. Rats were immunized with synthetic peptides, corresponding to amino acids 38–51 of mouse podoplanin or human podoplanin which is 100% homologous to the same site of monkey podoplanin; anti-mouse podoplanin mAb PMab-1 (IgG_2a) and anti-human mAb NZ-1.2 (IgG_2a) were established. In immunocytochemistry, the mouse melanoma B16-F10 and mouse podoplanin (mPDPN)-expressed CHO transfectant were stained by PMab-1; human lymphatic endothelial cells (LEC) and human podoplanin (hPDPN)-expressed squamous cell carcinoma HSC3 transfectant, were stained by NZ-1.2. Western-blot analysis detected an about 40-kDa protein in CHO-mPDPN and B16-F10 by PMab-1, and in HSC3-hPDPN and LEC by NZ-1.2. In frozen sections, PMab-1 reacted with mouse kidney, pulmonary alveoli, pulmonary pleura, and salivary gland myoepithelial cells while NZ-1.2 reacted to the human salivary gland myoepithelial cells. The immunostaining of paraffin-embedded sections also showed the reaction of PMab-1 or NZ-1.2 to the mouse or monkey kidney glomerulus, pulmonary alveoli, and lung lymphatic vessels. These results indicate that the two novel rat mAbs to the mouse and human/monkey podoplanin are useful for Western-blot and immunostaining of somatic tissues on paraffin-embedded sections as well as frozen sections.

Fibrohistiocytic tumors and related neoplasms in children and adolescents

Fibrohistiocytic tumors (FHTs) in children and adolescents range from the benign fibrous histiocytoma, or dermatofibroma, to a variety of intermediate and malignant neoplasms, such as dermatofibrosarcoma protruberans and high-grade undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma). Those tumors as a group are comprised of fibroblasts, myofibroblasts, and histiocytes-dendritic cells with a variably prominent inflammatory infiltrate consisting of lymphocytes and eosinophils. Dendritic cells are also a major constituent of another group of neoplasms that include Langerhans cell histiocytosis, follicular and interdigitating cell sarcomas, and juvenile xanthogranuloma. These latter tumors are considered in this discussion for the sake of differential diagnosis and their possible histogenetic relationship to FHTs. Recent studies have suggested that the relationship between the fibroblast and histiocyte in the FHTs may reflect the intrinsic capacity to transdifferentiate from one to the other morphologic and functional state. The so-called "facultative fibroblast," as a cell with fibroblastic and histiocytic properties, was discussed in the context of the fibrous xanthoma 50 years ago. Possibly the entire histogenetic concept of FHTs should be reconsidered in light of current studies.

The expression of podoplanin and classic cadherins in the mouse brain

Podoplanin is a transmembrane glycoprotein indirectly linked to classic cadherins through ezrin-actin networks. Recently, the overexpression of podoplanin in high-grade malignancy brain tumors has been reported. The aim of this study was to investigate the expression of podoplanin and classic cadherins in the mouse brain. Immunohistochemistry showed that podoplanin was expressed on ependymal cells and choroid plexus epithelial cells at the ventricle side of the cell surface and at the cell-cell junctions, and on retinal pigment epithelial cells and in the pia mater; P-cadherin between choroid plexus epithelial cells and endothelial cells at the basement membrane side of cell surface, and between retinal pigment epithelial cells; VE-cadherin on the PECAM-1 positive-choroid plexus endothelial cells of the fibrovascular core; and N-cadherin on the cell surface and at the cell-cell junctions of ependymal cells, and in the pia mater. The regions expressing podoplanin, P-cadherin, and VE-cadherin did not coincide. In real-time PCR analysis, the amounts of podoplanin and P- and N-cadherin mRNA were larger in the ventricular wall with choroid plexus than in the abdominal aorta and cerebrum. In the RT-PCR analysis, the intensities of amplicon for VE-cadherin mRNA were the same for the abdominal aorta, cerebrum, and ventricular wall with the choroid plexus, suggesting that mouse ependymal cells, choroid plexus epithelial cells, and glial cells under the pia mater have the ability to express podoplanin and P- and N-cadherins. Glial cells and retinal pigment epithelial cells may create barriers by podoplanin and classic cadherins as a rate-determining step for transmission of blood components.

Association of T-zone reticular networks and conduits with ectopic lymphoid tissues in mice and humans

Ectopic or tertiary lymphoid tissues (TLTs) are often induced at sites of chronic inflammation. They typically contain various hematopoietic cell types, high endothelial venules, and follicular dendritic cells; and are organized in lymph node-like structures. Although fibroblastic stromal cells may play a role in TLT induction and persistence, they have remained poorly defined. Herein, we report that TLTs arising during inflammation in mice and humans in a variety of tissues (eg, pancreas, kidney, liver, and salivary gland) contain stromal cell networks consisting of podoplanin(+) T-zone fibroblastic reticular cells (TRCs), distinct from follicular dendritic cells. Similar to lymph nodes, TRCs were present throughout T-cell-rich areas and had dendritic cells associated with them. They expressed lymphotoxin (LT) β receptor (LTβR), produced CCL21, and formed a functional conduit system. In rat insulin promoter-CXCL13-transgenic pancreas, the maintenance of TRC networks and conduits was partially dependent on LTβR and on lymphoid tissue inducer cells expressing LTβR ligands. In conclusion, TRCs and conduits are hallmarks of secondary lymphoid organs and of well-developed TLTs, in both mice and humans, and are likely to act as important scaffold and organizer cells of the T-cell-rich zone.

Value of D2-40 in the differential diagnosis of pleural neoplasms with emphasis on its positivity in solitary fibrous tumor

D2-40 is a new monoclonal antibody recognizing podoplanin and it is selective for lymphatic endothelium. Several studies have confirmed the reliability of D2-40 in the diagnosis of pleural malignant mesothelioma, but the evaluation of this antibody in other pleural neoplasms is limited. The aim of this study was to determine the diagnostic value of D2-40 in segregation of malignant mesothelioma from other pleural or lung neoplasms. Sixty-seven cases, including 36 pleural malignant mesotheliomas, 15 solitary fibrous tumors, 13 pleomorphic carcinomas, and 3 synovial sarcomas, were immunohistochemically studied using a D2-40 monoclonal antibody. Twenty-five (21 epithelioid and 4 biphasic) of 36 (69%) malignant mesotheliomas and 2 of 15 (13%) solitary fibrous tumors were positive for D2-40. The difference of D2-40 positivity between these 2 types of tumor was significant (P<0.001). No D2-40 positivity was detected in pleomorphic carcinomas (n=13) or synovial sarcomas (n=3). These findings showed that D2-40 was frequently positive in malignant mesothelioma, but could also be positive in a small portion of solitary fibrous tumor. These results indicate that D2-40 is a valuable marker for malignant mesothelioma, but caution should be taken when evaluating D2-40-positive pleural spindle cell neoplasms in limited small biopsy specimens, especially when the differential diagnosis includes solitary fibrous tumor and malignant mesothelioma.

Immunohistochemical examination for the distribution of podoplanin-expressing cells in developing mouse molar tooth germs

We recently reported the expression of podoplanin in the apical bud of adult mouse incisal tooth. This study was aimed to investigate the distribution of podoplanin-expressing cells in mouse tooth germs at several developing stages. At the bud stage podoplanin was expressed in oral mucous epithelia and in a tooth bud. At the cap stage podoplanin was expressed on inner and outer enamel epithelia but not in mesenchymal cells expressing the neural crest stem cell marker nestin. At the early bell stage nestin and podoplanin were expressed in cervical loop and odontoblasts. At the root formation stage both nestin and podoplanin were weakly expressed in odontoblasts generating radicular dentin. Podoplanin expression was also found in the Hertwig epithelial sheath. These results suggest that epithelial cells of developing tooth germ acquire the ability to express nestin, and that tooth germ epithelial cells maintain the ability to express podoplanin in oral mucous epithelia. The expression of podoplanin in odontoblasts was induced as tooth germ development advanced, but was suppressed with the completion of the primary dentin, suggesting that podoplanin may be involved in the cell growth of odontoblasts. Nestin may function as an intermediate filament that binds podoplanin in odontoblasts.

The WHO classification of lymphomas: cost-effective immunohistochemistry using a deductive reasoning "decision tree" approach: part II: the decision tree approach: diffuse patterns of proliferation in lymph nodes

The 2008 World Health Organization Classification of Tumors of the Haematopoietic and Lymphoid Tissues defines current standards of practice for the diagnosis and classification of malignant lymphomas and related entities. More than 50 different types of lymphomas are described. Faced with such a broad range of different lymphomas, some encountered only rarely, and a rapidly growing armamentarium of 80 or more pertinent immunohistochemical (IHC) "stains," the challenge to the pathologist is to use IHC in an efficient manner to arrive at an assured and timely diagnosis. This review uses deductive reasoning following a decision tree or dendrogram model, combining basic morphologic patterns and common IHC markers to classify node-based malignancies by the World Health Organization schema. The review is divided into 2 parts, the first addressing those lymphomas that produce a follicular or nodular pattern of lymph nodal involvement appeared in the previous issue of AIMM. The second part addresses diffuse proliferations in lymph nodes. Emphasis is given to the more common lymphomas and the more commonly available IHC "stains" for a pragmatic and practical approach that is both broadly feasible and cost-effective. By this method, an assured diagnosis may be reached in the majority of nodal lymphomas, at the same time developing a sufficiency of data to recognize those rare or atypical cases that require referral to a specialized center.

Follicular Dendritic Cell Tumor in Liver: A Case Report and Collective Review

Follicular dendritic cells (FDC) are a subset of the immune system and present in the germinal centers of lymphoid follicles in the spleen and lymph nodes. They are functionally as antigen-presenting cells and thus improving the quality of the humoral immune response. Follicular dendritic cell tumor is rare but considered low-grade sarcoma. Including our case, there were totally 17 cases with FDC tumor involved the liver from Medline. In these cases, the mean age was 47 years old, ranged from 19 to 82. It was much more common in females than in males (13:4). The clinical manifestations of these patients included abdominal discomfort, palpable mass, weight loss and malaise. The average size of the tumor was 11 cm. Most of the FDC tumors were associated with Epstein-Barr virus expression, 13/17 (76.5%). Surgical resection remains the mainstay of the treatment.

A follicular dendritic cell sarcoma of the mediastinum with immature T cells and association with myasthenia gravis

Follicular dendritic cell (FDC) sarcoma is a very rare neoplasm showing morphologic and phenotypic features of FDCs. It occurs primarily in lymph nodes but also in extranodal sites. So far, there have been no reports on FDC sarcoma associated with myasthenia gravis. In the following we will present a case of an FDC tumor of the mediastinum associated with paraneoplastic myasthenia gravis in a 39-year-old man. The tumor contained a major proportion of immature T cells, which may be connected to this patient's very unusual clinical presentation with autoimmune phenomena. Extranodal FDC sarcomas still seem hardly noticed, and their clinical and pathologic characteristics remain to be better defined.

Immunohistochemical examination on the distribution of cells expressed lymphatic endothelial marker podoplanin and LYVE-1 in the mouse tongue tissue

The clinical study for lingual disease requires the detailed investigation of the lingual lymphatic network and lymphatic marker-positive cells. Recently, it has been reported that several tissue cells and leukocytes express lymphatic markers, LYVE-1 and podoplanin. This study was aimed to clarify the lingual distribution of cells expressing LYVE-1 and podoplanin. In the mouse tongue, podoplanin is expressed in nerve sheaths, lingual gland myoepithelial cells, and lymphatic vessels. LYVE-1 is expressed in the macrophage marker Mac-1-positive cells as well as lymphatic vessels, while factor-VIII was detected in only blood endothelial cells. α-SMA was detected in vascular smooth muscle and myoepithelial cells. Therefore, identification of lymphatic vessels in lingual glands, the combination of LYVE-1 and factor-VIII, or LYVE-1 and Mac-1 is useful because myoepithelial cells express podoplanin and α-SMA. The immunostaining of factor-VIII on lymphatic vessels was masked by the immunostaining to LYVE-1 or podoplanin because lymphatic vessels express factor-VIII to a far lesser extent than blood vessels. Therefore, except for the salivary glands, the combination of podoplanin and α-SMA, or factor-VIII is useful to identify lymphatic vessels and blood vessels with smooth muscle, or blood capillaries.

Immunoelectron microscopic study of podoplanin localization in mouse salivary gland myoepithelium

We have recently reported that salivary gland cells express the lymphatic endothelial cell marker podoplanin. The present study was aimed to immunohistochemically investigate the expression of the myoepithelial cell marker α-smooth muscle actin (SMA) on podoplanin-positive cells in mouse parotid and sublingual glands, and to elucidate podoplanin localization in salivary gland myoepithelial cells by immunoelectron microscopic study. The distribution of myoepithelial cells expressing podoplanin and α-SMA was examined by immunofluorescent staining, and the localization of reaction products of anti-podoplanin antibody was investigated by pre-embedded immunoelectron microscopic method. In immunohistochemistry, the surfaces of both the mucous acini terminal portion and ducts were covered by a number of extensive myoepithelial cellular processes expressing podoplanin, and the immunostaining level with anti-podoplanin antibody to myoepithelial cells completely coincided with the immunostaining level with anti-α-SMA antibody. These findings suggest that podoplanin is a salivary gland myoepithelial cell antigen, and that the detection level directly reflects the myoepithelial cell distribution. In immunoelectron microscopic study, a number of reaction products with anti-podoplanin antibody were found at the Golgi apparatus binding to the endoplasmic reticulum in the cytoplasm of myoepithelial cells between sublingual gland acinar cells, and were also found at the myoepithelial cell membrane. These findings suggest that salivary gland myoepithelial cells constantly produce podoplanin and glycosylate at the Golgi apparatus, and transport them to the cell membrane. Podoplanin may be involved in maintaining the homeostasis of myoepithelial cells through its characteristic as a mucin-type transmembrane glycoprotein.

D2-40, a novel immunohistochemical marker in differentiating dermatofibroma from dermatofibrosarcoma protuberans

The distinction between dermatofibroma, particularly cellular variant, and dermatofibrosarcoma protuberans in excisional biopsies is usually straightforward. However, a separation between the two may be sometimes challenging, especially in superficial biopsies. Although factor XIIIa and CD34 immunostains are useful in differentiating dermatofibroma and dermatofibrosarcoma protuberans in most instances, focal CD34 positivity may be seen in cellular fibrous histiocytoma. Some cases reveal overlapping immunostain results. D2-40 identifies a 40-kDa O-linked sialoglycoprotein present on a variety of tissues including testicular germ cell tumors as well as lymphatic endothelium. In this study, we investigated the utility of D2-40 in separating dermatofibroma from dermatofibrosarcoma protuberans and compared the results with other commonly used immunostains. Fifty-six cases of dermatofibroma (including six cellular variant) and 29 cases of dermatofibrosarcoma protuberans were retrieved from the archives of Department of Anatomic Pathology at Sunnybrook Health Sciences Center in University of Toronto. We applied factor XIIIa, CD34, and monoclonal mouse anti-D2-40 immunostains to formalin-fixed, paraffin-embedded tissue sections. All 56 (100%) cases of dermatofibroma demonstrated strong and diffuse immunoreactivity to D2-40 in the spindle cells and stroma. Similarly, factor XIIIa showed strong and diffuse positivity in the spindle cells. Nearly all dermatofibromas were negative for CD34 except one case revealing focal positivity. None of dermatofibrosarcoma protuberans cases were labeled by D2-40, although four cases showed weak and patchy background staining in contrary to diffuse, strong, and crisp staining seen in dermatofibromas. Our results indicate that D2-40 seems to be a sensitive immunohistochemical marker for dermatofibromas, including cellular variant. Focal and faint D2-40 staining may be seen in the stroma of dermatofibrosarcoma protuberans. Our findings suggest that D2-40 can be used as a complementary immunostain to factor XIIIa and CD34 in problematic and challenging cases on superficial biopsies.