Peripheral Nerve Sheath Tumors in Patients With Neurofibromatosis Type 1: Morphological and Immunohistochemical Study.

BACKGROUND/AIM: The aim of the present investigation was to characterize the growth pattern and antigen profile of peripheral nerve sheath tumors (PNST) in a large series of tumors obtained from patients with Neurofibromatosis type 1 (NF1) focusing on morphological characteristics of diffuse plexiform neurofibroma (DPNF). MATERIALS AND METHODS: Tissue micro-array (TMA) analysis was applied to study 520 formalin-fixed, paraffin-embedded human PNST of 385 patients with confirmed NF1 diagnosis. PNST originated from all areas of the body and were classified as cutaneous neurofibroma (CNF, n=114), diffuse neurofibroma (DNF, n=109), DPNF (n=108), plexiform neurofibroma (PNF, n=110), and malignant peripheral nerve sheath tumor (MPNST, n=22). Histomorphology and antigen expression patterns of the tumors were determined [S100, epithelial membrane antigen (EMA), CD90, mast cell tryptase, and neurofilament]. RESULTS: Benign PNST showed significantly more S100-positive tumor cells than MPNST (p<0.001). EMA expression was most pronounced in perineurium of DPNF. The number of mast cells in CNF, DNF and DPNF was significantly higher compared to PNF and MPNST (p<0.001 for both comparisons, Mann-Whitney U-test). CONCLUSION: DPNF show some distinct cellular characteristics. A high number of EMA positive cells possibly indicates the dissemination of perineural cells to the surrounding tissue. Concerning mast cell density, DPNF resemble DNF and CNS rather than PNF. Close contact of tumor cells in DPNF, DNF and CNF with the immune system is a prerequisite for permanent immunological reactions in contrast to PNF in which tumor cells are partitioned from the immune system by the perineurium and blood-nerve barrier of blood vessels. It is assumed that these morphological distinctions may reflect in part the biological differences between the entities. While PNF is a known precancerous stage in NF1 patients, DPNF are not rated as such. Furthermore, the morphologic differences between benign nerve sheath tumors may be important for the efficacy of drugs to access tumor cells.

Thy1-Positive Spermatogonia Suppress the Proliferation of Spermatogonial Stem Cells by Extracellular Vesicles In Vitro.

The self-renewal of mammalian spermatogonial stem cells (SSCs) supports spermatogenesis to produce spermatozoa, and this is precisely controlled in a stem niche microenvironment in the seminiferous tubules. Although studies have revealed the role of the surrounding factors in SSCs, little is known about whether the division of SSCs is controlled by extracellular vesicles. Here, extracellular vesicles were found in the basal compartment of seminiferous tubules in mouse, rat, rabbit and human testes. In the mice, the testicular extracellular vesicles are secreted by spermatogonia and are taken up by SSCs. Further, the extracellular vesicles from thy1-positive spermatogonia were purified by anti-Thy1-coupled magnetic beads, which suppress their proliferation of SSCs but do not lead to the apoptosis in vitro.

AMD3100 redosing fails to repeatedly mobilize hematopoietic stem cells in the nonhuman primate and humanized mouse.

AMD3100 (plerixafor) is a vital component of many clinical and preclinical transplant protocols, facilitating harvest of hematopoietic stem and progenitor cells through mobilization into the peripheral blood circulation. Repeat mobilization with AMD3100 is also necessary for many patients with suboptimal first stem cell collection or those requiring repeat transplantation. In this study we investigated the mobilization efficacy of repeated AMD3100 dosages in the nonhuman primate and humanized mouse models. In nonhuman primates, we observed effective mobilization after the first AMD3100 administration but a significantly poorer response in CD34+ and hematopoietic stem cell-enriched CD90+ cells with subsequent doses of the drug. A similar loss of efficacy with repeated administration was noted in immunodeficient mice engrafted with human CD34+ cells, in whom the total human white cell population, and particularly human hematopoietic stem and progenitor cells, mobilized significantly less effectively following a second AMD3100 administration when compared with the first dose. Together, our results are expected to inform future mobilization protocols for the purposes of peripheral blood hematopoietic stem cell extraction or for applications in which hematopoietic stem cells must be made accessible for in vivo-delivered gene targeting agents.

Localized Cell-Surface Sampling of a Secreted Factor Using Cell-Targeting Beads.

Intercellular communication through the secretion of soluble factors plays a vital role in a wide range of biological processes (e.g., homeostasis, immune response), yet identification and quantification of many of these factors can be challenging due to their degradation or sequestration in cell culture media prior to analysis. Here, we present a customizable bead-based system capable of simultaneously binding to live cells (through antibody-mediated cell tethering) and capturing cell-secreted molecules. Our functionalized beads capture secreted molecules (e.g., hepatocyte growth factor secreted by fibroblasts) that are diminished when sampled via traditional supernatant analysis techniques (p < 0.05), effectively rescuing a reduced signal in the presence of neutralizing components in the cell culture media. Our system enables capture and analysis of molecules integral to chemical communication that would otherwise be markedly decreased prior to analysis.

Effect of culture duration on chondrogenic preconditioning of equine bone marrow mesenchymal stem cells in self-assembling peptide hydrogel.

Ex vivo induction of chondrogenesis is a promising approach to improve upon the use of bone marrow mesenchymal stem cells (MSCs) for cartilage tissue engineering. This study evaluated the potential to induce chondrogenesis with days of culture in chondrogenic medium for MSCs encapsulated in self-assembling peptide hydrogel. To simulate the transition from preconditioning culture to implantation, MSCs were isolated from self-assembling peptide hydrogel into an individual cell suspension. Commitment to chondrogenesis was evaluated by seeding preconditioned MSCs into agarose and culturing in the absence of the chondrogenic cytokine transforming growth factor beta (TGFß). Positive controls consisted of undifferentiated MSCs seeded into agarose and cultured in medium containing TGFß. Three days of preconditioning was sufficient to produce chondrogenic MSCs that accumulated ∼75% more cartilaginous extracellular matrix than positive controls by day 17. However, gene expression of type X collagen was ∼65-fold higher than positive controls, which was attributed to the absence of TGFß. Potential induction of immunogenicity with preconditioning culture was indicated by expression of major histocompatibility complex class II (MHCII), which was nearly absence in undifferentiated MSCs, and ∼7% positive for preconditioned cells. These data demonstrate the potential to generate chondrogenic MSCs with days of self-assembling peptide hydrogel, and the ability to readily recover an individual cell suspension that is suited for injectable therapies. However, continued exposure to TGFß may be necessary to prevent hypertrophy indicated by type X collagen expression, while immunogenicity may be a concern for allogeneic applications. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1368-1375, 2019.

Ex Vivo Detection of Circulating Tumor Cells from Whole Blood by Direct Nanoparticle Visualization.

The detection of circulating tumor cells (CTCs) from blood samples can predict prognosis, response to systemic chemotherapy, and metastatic spread of carcinoma. Therefore, approaches for CTC identification is an important aspect of current cancer research. Here, a method for the direct visualization of nanoparticle-coated CTCs under dark field illumination is presented. A metastatic breast cancer cell line (4T1) was transduced with a non-native target protein (Thy1.1). Positive 4T1-Thy1.1 cells incubated with antibody-coated metallic nanoshells appeared overly bright at low magnification, allowing a quick screening of samples and easy visual detection of even single isolated CTCs. The use of a nontransduced cell line as control creates the ideal scenario to evaluate nonspecific binding. A murine metastatic tumor model with the 4T1-Thy1.1 cell line was also implemented. Blood was drawn from mice over the course of one month, and CTCs were successfully detected in all positive subjects. This work validates the use of metallic nanoshells as labels for direct visualization of CTCs while providing guidelines to a systematic development of nanotechnology-based detection systems for CTCs.

Composition of the Stroma in the Human Endometrium and Endometriosis.

To analyze whether the endometrial and endometriotic microenvironment is involved in the pathogenesis of endometriosis, we characterized the stromal composition. We used CD90 for fibroblasts, α-smooth muscle actin for myofibroblasts as well as CD10 and CD140b for mesenchymal stromal cells. Quantification of eutopic endometrial stroma of cases without endometriosis showed a high percentage of stromal cells positive for CD140b (80.7%) and CD10 (67.4%), a moderate number of CD90-positive cells (57.9%), and very few α-smooth muscle actin-positive cells (8.5%). These values are highly similar to cases with endometriosis showing only minor changes: CD140b (76.7%), CD10 (63%), CD90 (53.9%), and α-smooth muscle actin (6.9%). There are no significant differences in the composition of CD140b- and CD10-positive stromal cells between the eutopic endometrial stroma and the 3 different endometriotic entities (ovarian, peritoneal, and deep infiltrating endometriosis), except for a significant difference between CD10-positive stromal cells in peritoneal lesions compared to ovarian lesions. However, the percentage of CD90-positive stromal cells was reduced in the 3 different endometriotic entities compared to the endometrium, especially significant in the ovarian lesions. In contrast, the percentage of α-smooth muscle actin-positive cells in the ovary was moderately increased. Taken together, the marker signature of eutopic endometrial and endometriotic stromal cells resembles mostly mesenchymal stromal cells. Our results show clearly that the proportion of the different stromal cell types in the endometrium with or without endometriosis does not differ significantly, thus suggesting that the stromal eutopic endometrial microenvironment does not contribute to the pathogenesis of endometriosis.

Immunophenotypical analysis of pancreatic interstitial cells in the developing rat pancreas and myofibroblasts in the fibrotic pancreas in dogs and cats.

Pancreatic fibrosis develops as the results of the activity of myofibroblasts capable of producing collagens. The myofibroblasts derive from pancreatic interstitial cells, including pancreatic stellate cells (PSCs), which can express glial fibrillary acidic protein (GFAP). First, we investigated the expression patterns of vimentin, desmin, α-smooth muscle actin (α-SMA), Thy-1 and GFAP in the developing rat pancreas (in fetuses at 18 and 20 days, neonates from 1 to 21 days, and adults). Interstitial cells in the developing pancreas expressed vimentin, desmin, GFAP and Thy-1 at varying degrees; interestingly, the reactivity for desmin and vimentin was the highest in fetuses. GFAP expression was consistent between fetuses and neonates, and Thy-1 reactivity transiently increased after birth; however, α-SMA-positive interstitial cells were rarely seen. Next, we analyzed the immunophenotypical characteristics of myofibroblasts appearing in pancreatic fibrosis in dogs and cats. With increasing fibrotic grade, myofibroblasts showed increased expression of vimentin, desmin and α-SMA, in addition to increased GFAP expression. Collectively, pancreatic interstitial cells and myofibroblasts may have similar immunophenotypes, and myofibroblasts might originate partly from GFAP-expressing PSCs.

Transient receptor potential melastatin 4 channel is required for rat dental pulp stem cell proliferation and survival.

OBJECTIVES: Investigate the role of the transient receptor potential melastatin 4 (TRPM4) channel in rat dental pulp stem cell (DPSC) proliferation and survival. MATERIALS AND METHODS: Immunofluorescence and FACS analysis were used to detect the stem cell marker CD90. Alizarin Red S and Oil Red O staining were used to identify osteoblast and adipocyte differentiation, respectively. To characterize TRPM4, patch-clamp recordings were obtained from single cells in the whole-cell configuration mode. The significance of TRPM4 for proliferation and survival was examined with 9-phenanthrol, a TRPM4 inhibitor during a 96-hour period of culture. Real-time Ca2+ imaging analysis with Fura-2AM was used to investigate the impact of TRPM4 on intracellular Ca2+ signals. RESULTS: DPSCs were CD90-positive and differentiated into osteoblasts. Patch-clamp recordings revealed currents typical of TRPM4 that were Ca2+ -activated, voltage-dependent and Na+ -conducting. Inhibition of TRPM4 resulted in a significant reduction in the cell population after a 96-hr period of culture and transformed the biphasic pattern of intracellular Ca2+ signalling into sustained oscillations. CONCLUSIONS: Rat DPSCs have stem cell characteristics and functional TRPM4 channels that are required for proliferation and survival. These data suggest that the shape and frequency of intracellular Ca2+ signals may mediate stem cell proliferation and survival.

Isolation, characterization and cold storage of cells isolated from diseased explanted livers.

INTRODUCTION: Livers discarded after standard organ retrieval are commonly used as a cell source for hepatocyte transplantation. Due to the scarcity of organ donors, this leads to a shortage of suitable cells for transplantation. Here, the isolation of liver cells from diseased livers removed during liver transplantation is studied and compared to the isolation of cells from liver specimens obtained during partial liver resection. METHODS: Hepatocytes from 20 diseased explanted livers (Ex-group) were isolated, cultured and stored at 4°C for up to 48 hours, and compared to hepatocytes isolated from the normal liver tissue of 14 liver lobe resections (Rx-group). The nonparenchymal cell fraction (NPC) was analyzed by flow cytometry to identify potential liver progenitor cells, and OptiPrep™ (Sigma-Aldrich) density gradient centrifugation was used to enrich the progenitor cells for immediate transplantation. RESULTS: There were no differences in viability, cell integrity and metabolic activity in cell culture and survival after cold storage when comparing the hepatocytes from the Rx-group and the Ex-group. In some cases, the latter group showed tendencies of increased resistance to isolation and storage procedures. The NPC of the Ex-group livers contained considerably more EpCAM+ and significantly more CD90+ cells than the Rx-group. Progenitor cell enrichment was not sufficient for clinical application. CONCLUSIONS: Hepatocytes isolated from diseased explanted livers showed the essential characteristics of being adequate for cell transplantation. Increased numbers of liver progenitor cells can be isolated from diseased explanted livers. These results support the feasibility of using diseased explanted livers as a cell source for liver cell transplantation.

Efectos divergentes del factor de crecimiento endotelial vascular, VEGF y el fragmento N-terminal de la proteína relacionada con la parathormona, PTHrP en células madre mesenquimales derivadas de tejido adiposo humano / No disponible

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Multiple roles of CD90 in cancer.

THY1 (CD90) is a 25-37-kDa heavily N-glycosylated, glycophosphatidylinositol (GPI) anchored cell surface protein. It is usually expressed on thymocytes, mesenchymal stem cells, hematopoietic stem cells, natural killer cells, neurons, endothelial cells, renal glomerular mesangial cells, follicular dendritic cells, fibroblasts, and myofibroblasts. It has been found to regulate cell adhesion, migration, apoptosis, axon growth, cell-cell and cell-matrix interactions, T-cell activation, and fibrosis. Several reports have shown that CD90 has an important role in cancer in regulating cancer cell proliferation, metastasis, and angiogenesis. There are also evidences that CD90 is an important prognostic marker in many cancers. Consequently, therapies that target CD90 have great promise in treating many cancers. However, several studies also indicate a contradictory role for CD90, where it acts as a tumor suppressor. In this review, we summarize the expression, function of CD90 in different cancers and its possible use as a biomarker or a therapeutic target in cancer. The challenges and future prospects for the use of CD90 for clinical applications are also discussed in this review.

Isolation of CD 90+ Fibroblast/Myofibroblasts from Human Frozen Gastrointestinal Specimens.

Fibroblasts/myofibroblasts (MFs) have been gaining increasing attention for their role in pathogenesis and their contributions to both wound healing and promotion of the tumor microenvironment. While there are currently many techniques for the isolation of MFs from gastrointestinal (GI) tissues, this protocol introduces a novel element of isolation of these stromal cells from frozen tissue. Freezing GI tissue specimens not only allows the researcher to acquire samples from worldwide collaborators, biobanks, and commercial vendors, it also permits the delayed processing of fresh samples. The described protocol will consistently yield characteristic spindle-shaped cells with the MF phenotype that express the markers CD90, α-SMA and vimentin. As these cells are derived from patient samples, the use of primary cells also confers the benefit of closely mimicking MFs from disease states-namely cancer and inflammatory bowel diseases. This technique has been validated in gastric, small bowel, and colonic MF primary culture generation. Primary MF cultures can be used in a vast array of experiments over a number of passage and their purity assessed by both immunocytochemistry and flow cytometry analysis.

MSC surface markers (CD44, CD73, and CD90) can identify human MSC-derived extracellular vesicles by conventional flow cytometry.

BACKGROUND: Human mesenchymal stromal cells (hMSC) are multipotent cells with both regenerative and immunomodulatory activities making them an attractive tool for cellular therapy. In the last few years it has been shown that the beneficial effects of hMSC may be due to paracrine effects and, at least in part, mediated by extracellular vesicles (EV). EV have emerged as important mediators of cell-to-cell communication. Flow cytometry (FCM) is a routine technology used in most clinical laboratories and could be used as a methodology for hMSC-EV characterization. Although several reports have characterized EV by FCM, a specific panel and protocol for hMSC-derived EV is lacking. The main objective of our study was the characterization of hMSC-EV using a standard flow cytometer. METHODS: Human MSC from bone marrow of healthy donors, mesenchymal cell lines (HS-5 and hTERT) and a leukemic cell line (K562 cells) were used to obtain EV for FCM characterization. EV released from the different cell lines were isolated by ultracentrifugation and were characterized, using a multi-parametric analysis, in a conventional flow cytometer. EV characterization by transmission electron microscopy (TEM), western blot (WB) and Nano-particle tracking analysis (NTA) was also performed. RESULTS: EV membranes are constituted by the combination of specific cell surface molecules depending on their cell of origin, together with specific proteins like tetraspanins (e.g. CD63). We have characterized by FCM the EV released from BM-hMSC, that were defined as particles less than 0.9 µm, positive for the hMSC markers (CD90, CD44 and CD73) and negative for CD34 and CD45 (hematopoietic markers). In addition, hMSC-derived EV were also positive for CD63 and CD81, the two characteristic markers of EV. To validate our characterization strategy, EV from mesenchymal cell lines (hTERT/HS-5) were also studied, using the leukemia cell line (K562) as a negative control. EV released from mesenchymal cell lines displayed the same immunophenotypic profile as the EV from primary BM-hMSC, while the EV derived from K562 cells did not show hMSC markers. We further validated the panel using EV from hMSC transduced with GFP. Finally, EV derived from the different sources (hMSC, hTERT/HS-5 and K562) were also characterized by WB, TEM and NTA, demonstrating the expression by WB of the exosomal markers CD63 and CD81, as well as CD73 in those from MSC origin. EV morphology and size/concentration was confirmed by TEM and NTA, respectively. CONCLUSION: We described a strategy that allows the identification and characterization by flow cytometry of hMSC-derived EV that can be routinely used in most laboratories with a standard flow cytometry facility.

Association of CD34+ and CD90+ Stem Cells of Cord Blood with Neonatal Factors: A Cross-sectional Study.

OBJECTIVE: To characterize the primitive stem cell content of cord blood with regard to neonatal parameters. METHODS: In this cross-sectional study, CD34+ and CD90+ cells content were enumerated by flow-cytometry method. Their associations with various neonatal parameters like birth weight, gender, gestational age and mode of delivery were analyzed by univariate analysis. Multivariable linear regression model was then developed to further explain the effect of neonatal factors on these primitive cell counts. RESULTS: From a total of 106 recruited subjects, gender of the neonate did not have any influence on the expression of these proteins (CD34 and CD90) of cord blood stem cells or progenitors. Multi variable linear regression analysis using CD34+ and CD90+ cell counts as dependent variables revealed that birth weight and the mode of delivery were significant predictors of these cell counts. CONCLUSIONS: The present study suggests that birth weight and mode of delivery of the neonates influences cord blood stem cell yield.

Purified Human Dental Pulp Stem Cells Promote Osteogenic Regeneration.

Human dental pulp stem/progenitor cells (hDPSCs) are attractive candidates for regenerative therapy because they can be easily expanded to generate colony-forming unit-fibroblasts (CFU-Fs) on plastic and the large cell numbers required for transplantation. However, isolation based on adherence to plastic inevitably changes the surface marker expression and biological properties of the cells. Consequently, little is currently known about the original phenotypes of tissue precursor cells that give rise to plastic-adherent CFU-Fs. To better understand the in vivo functions and translational therapeutic potential of hDPSCs and other stem cells, selective cell markers must be identified in the progenitor cells. Here, we identified a dental pulp tissue-specific cell population based on the expression profiles of 2 cell-surface markers LNGFR (CD271) and THY-1 (CD90). Prospectively isolated, dental pulp-derived LNGFR(Low+)THY-1(High+) cells represent a highly enriched population of clonogenic cells--notably, the isolated cells exhibited long-term proliferation and multilineage differentiation potential in vitro. The cells also expressed known mesenchymal cell markers and promoted new bone formation to heal critical-size calvarial defects in vivo. These findings suggest that LNGFR(Low+)THY-1(High+) dental pulp-derived cells provide an excellent source of material for bone regenerative strategies.

Blood vessels expressing CD90 in human and rat brain tumors.

Blood vessels in brain tumors, particularly glioblastomas, have been shown to express CD90. CD90(+) cells in and around blood vessels in cancers including brain tumors have been identified as endothelial cells, cancer stem cells, fibroblasts or pericytes. In this study, we aimed to determine the nature or type(s) of cells that express CD90 in human brain tumors as well as an experimental rat glioma model by double immunofluorescence staining. The majority of CD90(+) cells in human glioblastoma tissue expressed CD31, CD34 and von Willebrand factor, suggesting that they were endothelial cells. Vasculatures in a metastatic brain tumor and meningioma also expressed CD90. CD90(+) cells often formed glomeruloid structures, typical of angiogenesis in malignant tumors, not only in glioblastoma but also in metastatic tumors. Some cells in the middle and outer layers of the vasculatures expressed CD90. Similar results were obtained in the rat glioma model. There were cells expressing both α-smooth muscle actin and CD90 in the middle layer of blood vessels, indicating that smooth muscle cells and/or pericytes may express CD90. CD90(+) vasculatures were surrounded by tumor-associated macrophages (TAMs). Thus, in addition to endothelial cells, some other types of cells, such as smooth muscle cells, pericytes and fibroblasts constituting the vasculature walls in brain tumors expressed CD90. Because CD90 has been shown to interact with integrins expressed by circulating monocytes, CD90 might be involved in angiogenesis through recruitment and functional regulation of TAMs in tumors. CD90(+) vasculatures may also interact with tumor cells through interactions with integrins. Because CD90 was not expressed by vasculatures in normal brain tissue, it might be a possible therapeutic target to suppress angiogenesis and tumor growth.

Generation of Tissue Sections for Screening Thy1 Mouse Lines.

New generations of Thy1-XFP transgenic mice (where XFP stands for any fluorescent protein) can now be readily generated, given the availability of core facilities or commercial providers of Thy1 pronuclear injections. Here, we provide a protocol for screening founder progeny. Transcardial perfusion is performed on 3-wk-old F1 mice that have been produced by crossing Thy1 transgenic founders and commercially obtained inbred mice. Cryosections are generated, and Thy1-driven expression is detected by histological characterization.

Imaging Acute Neuromuscular Explants from Thy1 Mouse Lines.

Because core facilities that generate transgenic founder mice for a reasonable fee are now available at most major research institutions, generating new Thy1-XFP transgenic animals (in which XFP stands for any fluorescent protein) is an option even for relatively small laboratories. Here, we provide a protocol for screening offspring of Thy1 transgenic founders. Acute neuromuscular explants are obtained from 3-wk-old F1 mice that have been produced by crossing Thy1 transgenic founders and commercially obtained inbred mice. Thy1-driven expression is detected by fluorescence microscopy.

Characterisation of lymphocyte subpopulations in infantile haemangioma.

AIMS: Interstitial CD45+ cells and T lymphocytes have previously been demonstrated within infantile haemangioma (IH). This study investigated the expression of B and T lymphocyte markers by the CD45+ population, and the expression of Thy-1, a marker of thymocyte progenitors, which have the ability to give rise to both B and T cells. METHODS: Immunohistochemical (IHC) staining was performed on proliferating and involuted IHs for the expression of CD45, CD3, CD20, CD79a, Thy-1 and CD34. The presence of mRNA corresponding to CD45, CD3G, CD20 and Thy-1 was confirmed by reverse transcriptase-polymerase chain reaction in snap-frozen IH tissues. Cell counting of 3,3-diaminobenzidine IHC-stained slides was performed on CD45+ only cells and dually stained CD45+/CD3+ cells or CD45+/CD20+ cells and analysed statistically. In situ hybridisation and mass spectrometry were also performed to confirm the presence and abundance of Thy-1, respectively. RESULTS: IHC staining showed a subpopulation of CD45+ interstitial cells that expressed the T lymphocyte marker, CD3, and another subpopulation that expressed the B lymphocyte marker, CD20, in proliferating and diminished in involuted IHs. The abundant expression of Thy-1 on the endothelium of proliferating, but not involuted IH, was demonstrated by IHC staining and confirmed by in situ hybridisation and mass spectrometry. CONCLUSIONS: Both B and T lymphocytes are present within the interstitium of proliferating and involuted IH. The expression of Thy-1 by the endothelium suggests that B and T cells in IH may have originated from within the lesion, rather than migrating from the peripheral circulation.