Serous fluid cytology of multicentric Castleman’s disease and other lymphoproliferative disorders associated with Kaposi sarcoma‐associated herpes virus: a review with case reports

C. Lobo, S. Amin, A. Ramsay, T. Diss and G. Kocjan Serous fluid cytology of multicentric Castleman’s disease and other lymphoproliferative disorders associated with Kaposi sarcoma‐associated herpes virus: a review with case reports Objective: The aim of this study is to describe and review the cytological features of Kaposi sarcoma‐associated herpes virus (KSHV) related entities, such as multicentric Castleman’s disease (MCD), plasmablastic‐lymphoma (PBL) and primary effusion lymphoma (PEL), which all may present as body cavity effusions. Serous fluid cytology of MCD and PBL has not, to our knowledge, thus far been described. Although different in nature, MCD, PBL and PEL are characterized by similar morphological features. Materials and methods: Body cavity effusions from four different patients with previously known or unknown KSHV‐related lymphoproliferations have been examined by routine cytology, immunocytochemistry (IC) and polymerase chain reaction (PCR). Results: MCD, PBL and PEL are all characterized by increased cellularity, comprising mainly lymphoid and plasmacytoid cells with variable proportions of immunoblasts. Immunocytochemistry and PCR results show the MCD to be CD138 and KSHV positive, CD30 negative, IgM, IgH and lambda restricted but IgH polyclonal. PBL was CD138 positive, kappa restricted, weakly positive with VS38 and over 80% positive with MIB 1. PEL was CD45, EMA, CD138, KSHV, p53 and CD3 positive, CD20, EBV, CD30, CD2, CD4, ALK1, epithelial and mesothelial markers negative, and PCR monoclonal B‐cell expanded (Ig‐kappa bands). Conclusion: Cytological examination of effusions in KSHV‐related lymphoproliferative disorders may show similar morphological features but clonality studies and immunocytochemistry are very helpful in distinguishing between these rare benign and malignant lymphoproliferative diseases.     

Amnion Epithelial Cells of Buffalo (Bubalus bubalis) Term Placenta Expressed Embryonic Stem Cells Markers and Differentiated into Cells of Neurogenic Lineage In Vitro

Aim of the present study was the isolation, culture, and characterization of amniotic membrane-derived epithelial cells (AE) from term placenta collected postpartum in buffalo. We found that cultured cells were of polygonal in shape, resistance to trypsin digestion and expressed cytokeratin-18 indicating that they were of epithelial origin. These cells have negative expression of mesenchymal stem cell markers (CD29, CD44, and CD105) and positive for pluripotency marker (OCT4) genes indicated that cultured cells were not contaminated with mesenchymal stem cells. Immunofluorescence staining with pluripotent stem cell surface markers, SSEA-1, SSEA-4, TRA-1-60, and TRA-1-81 indicated that these cells may retain pluripotent stem cell characteristics even after long period of differentiation. Differentiation potential of these cells was determined by their potential to differentiate into cells of neurogenic lineages using retinoic acid. In conclusion, we demonstrate that AE cells expressed pluripotent stem cell markers and have propensity to differentiate into cells of neurogenic lineage upon directed differentiation in vitro.     

Malignant ascites of serous papillary ovarian adenocarcinoma. An immunocytochemical study of the tumor cells

In 17 malignant peritoneal effusions due to papillary serous adenocarcinoma of the ovary, the reaction patterns of the tumor cells to monoclonal antibodies (MAbs) against surface antigens were studied and compared with the reaction patterns of mesothelial cells in the same effusions. The following surface markers were used with the adhesive slide method: epithelial membrane antigen (EMA), human epithelium-specific cell surface antigen (HEA-125), human endothelial antigen (BMA-120), carcinoembryonic antigen (CEA 3-13), an antibody against natural killer cells and cytotoxic cells (BMA-070), granulocyte antigen (Leu M1) and leukocyte antigen of class I (HLA-1). In all cases, from 30% to 95% of the tumor cells reacted with EMA and HEA-125. Tumor cells showed a positive staining with CEA 3-13 in only five cases. In all cases, from 75% to 95% of the tumor cells reacted positively with BMA-120. The reactivity of a few mesothelial cells with EMA and of all mesothelial cells with BMA-120 did not interfere with the identification of positive tumor cells since the reaction patterns were different. Interestingly, our study demonstrated that BMA-070, an MAb identifying natural killer cells and cytotoxic cells, is also a most useful tumor marker. The same was found to be true for Leu M1, an MAb originally thought to react only with granulocytes. The tumor cells showed a partial or total loss of the expression of HLA-1 reactivity. Since all cases were immunocytochemically positive for tumor cells while conventional cytology was positive in only 13 of the cases, the immunocytochemical analysis of malignant peritoneal effusions due to papillary serous adenocarcinoma of the ovary seems able to improve the cytologic diagnosis of the fluids.     

Identification of carcinoma cells in ascitic and pleural fluid. Comparison of four panepithelial antigens with carcinoembryonic antigen.

The cell membrane antigens epithelial membrane antigen (EMA), epithelial glycoprotein 34, (egp34), BW-495 and tumor-associated antigen 72 (TAG-72) are present in most benign and malignant epithelial cells and can be demonstrated with the help of monoclonal antibodies. In a study on the identification of carcinoma cells in samples of ascitic and pleural fluid involving 170 patients, we compared the value of immunocytochemical labeling of these antigens with that of immunocytochemical demonstration of carcinoembryonic antigen (CEA). Antibodies to EMA and egp34 occasionally also reacted with reactively proliferating mesothelial cells in benign conditions and thus appear to be inappropriate for diagnostic use. Cells positive for BW-495, TAG-72 and CEA, however, have never been found in benign conditions; the specificity of these antigens thus permits their use in diagnosis. Antigen-expressing cells were found in 85% (BW-495), 62% (TAG-72) and 60% (CEA) of cytologically positive samples from carcinoma patients. Similarly, positive reactions for BW-495, TAG-72 and CEA were observed in, respectively, 36%, 29% and 34% of cytologically negative or suspicious samples. BW-495 thus appears to be a suitable marker for the demonstration of carcinoma cells in samples of pleural and ascitic fluid and to have a higher degree of sensitivity than does either TAG-72 or CEA.     

Higher expression of SATB2 in hepatocellular carcinoma of African Americans determines more aggressive phenotypes than those of Caucasian Americans

In the United States, Hepatocellular Carcinoma (HCC) incidence has tripled over the past two decades. The disease has disproportionately affected minority and disadvantaged populations. The purpose of this study was to examine the expression of SATB2 gene in HCC cells derived from African Americans (AA) and Caucasian Americans (CA) and assess its oncogenic potential by measuring cell viability, spheroid formation, epithelial‐mesenchymal transition (EMT), stem cell markers and pluripotency maintaining factors in cancer stem cells (CSCs). We compared the expression of SATB2 in human primary hepatocytes, HCC cells derived from AA and CA, and HCC CSCs. Hepatocellular carcinoma cells derived from AA expressed the higher level of SATB2 than those from CA. By comparison, normal human hepatocytes did not express SATB2. Higher expression of SATB2 in HCC cells from AA was associated with greater growth rate, cell viability, colony formation and EMT characteristics than those from CA. Knockout of SATB2 in CSCs by Crispr/Cas9 technique significantly inhibited the expression of SATB2 gene, stem cell markers (CD24, CD44 and CD133), pluripotency maintaining factors (c‐Myc, KLF4, SOX2 and OCT4), and EMT compared with non‐targeting control group. The expression of SATB2 was negatively correlated with miR34a. SATB2 rescued the miR‐34a‐mediated inhibition of CSC's viability. These data suggest that SATB2 is an oncogenic factor, and its higher expression may explain the disparity in HCC outcomes among AA.     

Human breast milk is a rich source of multipotent mesenchymal stem cells

Putative stem cells have been isolated from various tissue fluids such as synovial fluid, amniotic fluid, menstrual blood, etc. Recently the presence of nestin positive putative mammary stem cells has been reported in human breast milk. However, it is not clear whether they demonstrate multipotent nature. Since human breast milk is a non-invasive source of mammary stem cells, we were interested in examining the nature of these stem cells. In this pursuit, we could succeed in isolating and expanding a mesenchymal stem cell-like population from human breast milk. These cultured cells were examined by immunofluorescent labeling and found positive for mesenchymal stem cell surface markers CD44, CD29, SCA-1 and negative for CD33, CD34, CD45, CD73 confirming their identity as mesenchymal stem cells. Cytoskeletal protein marker analysis revealed that these cells expressed mesenchymal stem cells markers, namely, nestin, vimentin, smooth muscle actin and also manifests presence of E-Cadherin, an epithelial to mesenchymal transition marker in their early passages. Further we tested the multipotent differentiation potential of these cells and found that they can differentiate into adipogenic, chondrogenic and oesteogenic lineage under the influence of specific differentiation cocktails. This means that these mesenchymal stem cells isolated from human breast milk could potentially be “reprogrammed” to form many types of human tissues. The presence of multipotent stem cells in human milk suggests that breast milk could be an alternative source of stem cells for autologous stem cell therapy although the significance of these cells needs to be determined.     

Usefulness of ploidy, AgNOR and immunocytochemistry for differentiating benign and malignant cells in serous effusions

OBJECTIVE: The objective of this study was to establish the value of different markers in differentiating reactive mesothelial cells from metastatic adenocarcinomatous cells in serous effusions (SE). METHODS: Forty-five SE were processed for morphological examination (Papanicolaou stain), assessment of ploidy, AgNOR counting and immunocytochemical assay of carcinoembryonic antigen (CEA), epithelial membrane antigens (EMA), Ber-EP4 and Leu-M1. Ploidy was established in an image-analyser in smears stained by the Feulgen stain method. AgNOR dots were counted in the smears stained with the silver nitrate assay for non-histone proteins present in the nucleolar organizer region. CEA, EMA, Ber-EP4 and Leu-M1 were evaluated by immunocytochemistry using the streptavidin-biotin complex method. RESULTS: All the smears with positive cytology were aneuploid. Three false negatives by morphological studies were aneuploid, with AgNOR values in two of them corresponding to the neoplastic group. CEA and Leu-M1 showed a low specificity; EMA and Ber-EP4 showed moderate sensitivity. CONCLUSIONS: The assessment of ploidy and the study of AgNOR were better methods than immunocytochemistry for distinguishing between reactive mesothelial cells and adenocarcinomatous cells in serous fluid.     

Limbal niche cells are a potent resource of adult mesenchymal progenitors

Limbal niche cells located in the limbal Palisades of Vogt are mesenchymal stem cells that reside next to limbal basal epithelial cells. Limbal niche cells are progenitors that express embryonic stem cell markers such as Nanog, Nestin, Oct4, Rex1, Sox2 and SSEA4, mesenchymal cell markers such as CD73, CD90 and CD105, and angiogenesis markers such as Flk‐1, CD31, CD34, VWF, PDGFRβ and α‐SMA, but negative for CD45. In addition, the stemness of limbal niche cells can be maintained during their cell culture in a three‐dimension environment. Furthermore, expanded limbal niche cells have the capability to undergo adipogenesis, chondrogenesis, osteogenesis and endogenesis in vitro, indicating that they are in fact a valuable resource of adult progenitors. Furthermore studies on how the limbal niche cells regulate the aforementioned stemness and corneal fate decision are warranted, as those investigations will shed new light on how mesenchymal progenitors reverse limbal stem cell deficiency and lead to new methods for limbal niche cell treatment.     

Mobilization of bone marrow-derived progenitor cells in acute coronary syndromes

Two hypotheses explain the role of adult progenitor cells in myocardial regeneration. Stem cell plasticity which involves mobilization of stem cells from the bone marrow and other niches, homing to the area of tissue injury and transdifferentiation into functional cardiomyocytes. Alternative hypothesis is based on the observations that bone marrow harbors a heterogenous population of cells positive for CXCR4 - receptor for chemokine SDF-1. This population of non-hematopoietic cells expresses genes specific for early muscle, myocardial and endothelial progenitor cells (EPC). These tissue-committed stem cells circulate in the peripheral blood at low numbers and can be mobilized by hematopoietic cytokines in the setting of myocardial ischemia. Endothelial precursors capable of transforming into mature, functional endothelial cells are present in the pool of peripheral mononuclear cells in circulation. Their number significantly increases in acute myocardial infarction (AMI) with subsequent decrease after 1 month, as well as in patients with unstable angina in comparison to stable coronary heart disease (CHD). There are numerous physiological and pathological stimuli which influence the number of circulating EPC such as regular physical activity, medications (statins, PPAR-gamma agonists, estrogens), as well as numerous inflammatory and hematopoietic cytokines. Mobilization of stem cells in AMI involves not only the endothelial progenitors but also hematopoietic, non-hematopoietic stem cells and most probably the mesenchymal cells. In healthy subjects and patients with stable CHD, small number of circulating CD34+, CXCR4+, CD117+, c-met+ and CD34/CD117+ stem cells can be detected. In patients with AMI, a significant increase in CD34+/CXCR4+, CD117+, c-met+ and CD34/CD117+ stem cell number the in peripheral blood was demonstrated with parallel increase in mRNA expression for early cardiac, muscle and endothelial markers in peripheral blood mononuclear cells. The maximum number of stem cells was found early in ST-segment elevation myocardial infarction (<12 hours) with subsequent decrease through the 7-day follow-up and with concomitant changes in the levels of cytokines involved in the inflammatory response and stem cell recruitment. Moreover, peak expression of cardiac muscle and endothelial markers occurred at the same time as the most significant increase in CD34/CXCR4+ stem cell number. The SDF-1/CXCR-4 axis seems particularly important in stem/muscle progenitor cell homing, chemotaxis, engraftment and retention in ischaemic myocardium. The significance of autologous stem cells mobilization in terms of cardiac salvage and regeneration needs to be proved in humans but it seems to be a reparative mechanism triggered early in the course of acute coronary syndromes.     

Mesenchymal stem cells support expansion of in vitro irradiated CD34(+) cells in the presence of SCF, FLT3 ligand, TPO and IL3: potential application to autologous cell therapy in accidentally irradiated victims

Ex vivo expansion of residual autologous hematopoietic stem and progenitor cells collected from victims soon after accidental irradiation (autologous cell therapy) may represent an additional or alternative approach to cytokine therapy or allogeneic transplantation. Peripheral blood CD34+ cells could be a useful source of cells for this process provided that collection and ex vivo expansion of hematopoietic stem and progenitor cells could be optimized. Here we investigated whether mesenchymal stem cells could sustain culture of irradiated peripheral blood CD34+ cells. In vitro irradiated (4 Gy 60Co gamma rays) or nonirradiated mobilized peripheral blood CD34+ cells from baboons were cultured for 7 days in a serum-free medium supplemented with stem cell factor+thrombopoietin+interleukin 3+FLT3 ligand (50 ng/ml each) in the presence or absence of mesenchymal stem cells. In contrast to cultures without mesenchymal stem cells, irradiated CD34+ cells cultured with mesenchymal stem cells displayed cell amplification, i.e. CD34+ (4.9-fold), CD34++ (3.8-fold), CD34++/Thy-1+ (8.1-fold), CD41+ (12.4-fold) and MPO+ (50.6-fold), although at lower levels than in nonirradiated CD34+ cells. Fourteen times more clonogenic cells, especially BFU-E, were preserved when irradiated cells were cultured on mesenchymal stem cells. Moreover, we showed that the effect of mesenchymal stem cells is related mainly to the reduction of apoptosis and involves cell-cell contact rather than production of soluble factor(s). This experimental model suggests that mesenchymal stem cells could provide a crucial tool for autologous cell therapy applied to accidentally irradiated victims.     

The value of epithelial membrane antigen in the diagnosis of ovarian tumors.

The value of epithelial membrane antigen (EMA) in the diagnosis of ovarian tumors was investigated using an indirect immunoperoxidase staining technique on 91 histologic sections (88 tumors and 3 normal tissues) and 39 ascitic fluid smears (28 from patients with epithelial ovarian tumors and 11 from cases of myoma uteri). The rate of positive EMA staining was highest in malignant tumors (89.2%), second highest in tumors of low malignant potential (33.3%) and lowest in benign tumors (25.0%); normal ovarian tissues were negative for EMA. Of the malignant tumors, all 48 serous cystadenocarcinomas (100%) and 18 of 26 mucinous cystadenocarcinomas (69.2%) stained positively for EMA. In serous cystadenocarcinomas, the EMA staining was mainly localized on the luminal membrane of cells in well-differentiated tumors, but appeared on the entire cell surface and cytoplasm of cells in poorly differentiated tumors. The results of EMA staining on ascitic fluid smears were almost the same as the results for the histologic sections. The intensity and the localization of EMA staining were related to the grade of malignancy in these ovarian tumors. In comparison with staining for other antigens (carcinoembryonic antigen, CA-125 and human keratin protein), EMA was found to be one of the most sensitive markers for the diagnosis of ovarian cancer.     

CEA, ZGM and EMA localization in cells of pleural and peritoneal effusion: a preliminary study

Carcinoembryonic antigen (CEA), the zinc glycinate marker (ZGM) and epithelial membrane antigen (EMA) have been described as epithelial or tumour markers of varying specificity. These antigens were studied by immunoperoxidase localization in selected cell blocks of 62 pleural or peritoneal effusions and compared to cytological findings and review of the clinical records. By cytological criteria, 25 of the cell blocks were positive for malignancy, 30 negative, and 7 inconclusive. CEA, ZGM, and EMA by immunoperoxidase staining were localized on the cell surface and often in the cytoplasm of malignant cells, in 11/25 (44 per cent), 17/25 (68 per cent) and 22/25 (88 per cent) of the positive cell blocks respectively. Ten (40 per cent) of these cases were positive for all three antigens, 7 (28 per cent) for two, and 6 (24 per cent) for one. Of the 7 cases which were inconclusive on routine cytological reporting, 5 were positive for at least one marker. In 3 of the 5 a diagnosis of malignancy was confirmed, and in the other two was strongly suspected as malignant on clinical grounds. Macrophages were sometimes positive for one or more markers (but showed cytoplasmic staining only) and mesothelial cells in some cases stained positively for EMA but were always negative for CEA and ZGM. Localization of the 3 antigens in cells of malignant effusions was compared with their localization in the primary tumours in 9 cases. Localization corresponded for CEA in 7 of 9 cases, for EMA in 8 of 8 an for ZGM in only 2 of 9. Effusion fluid levels for CEA were compared with the cytological and immunocytochemical findings in 30 cases. Mucin stains performed on the cell blocks were also compared with the immunoperoxidase findings.     

Circulating CD34+ hematopoietic progenitors in the harvesting peripheral blood stem cells; enhancement by recombinant human granulocyte colony-stimulating factor

The number of circulating progenitor cells increases during the period of hematopoietic recovery following myeloablative therapy. These progenitor cells were used for autologous transplantation in order to reconstitute hematopoiesis. As an indicator of the circulating progenitor cells, the number of granulocyte-macrophage colony forming units (CFU-GM), which is measured by means of a long-term cell culture, has been widely used. Recently, a cell surface marker, CD34, which can easily be measured by means of flowcytometry, was found to represent immature hematopoietic progenitor cells, which are very close to stem cells. Therefore, the relationship between the number of CD34 positive cells (CD34⁺ cells) and the number of CFU-GM in the peripheral blood following chemotherapy was studied in 9 patients selected to undergo autotransplantation. The number of peripheral blood CD34+ cells was found to be significantly correlated with that of CFU-GM (r = 0.81). When four out of 9 patients received recombinant human granulocyte-colony stimulating factor (rG-CSF) administration, a significant increase in the release of peripheral blood CD34⁺ cells as well as peripheral blood CFU-GM was observed (P<0.01). Thus, the measurement of CD34⁺ cells is useful for predicting the number of circulating CFU-GM.     

Long-term cultured human neural stem cells undergo spontaneous transformation to tumor-initiating cells

In this report, we describe the spontaneous malignant transformation of long-term cultured human fetal striatum neural stem cells (hsNSCs, passage 17). After subcutaneous transplantation of long-term cultured hsNSCs into immunodeficient nude mice, 2 out of 15 mice formed xenografts which expressed neuroendocrine tumor markers CgA and NSE. T1 cells, a cell line that we derived from one of the two subcutaneous xenografts, have undergone continuous expansion in vitro. These T1 cells showed stem cell-like features and expressed neural stem cell markers nestin and CD133. The T1 cells were involved in abnormal karyotype, genomic instability and fast proliferation. Importantly, after long-term in vitro culture, the T1 cells did not result in subcutaneous xenografts, but induced intracranial tumor formation, indicating that they adjusted themselves to the intracranial microenvironment. We further found that the T1 cells exhibited an overexpressed level of EGFR, and the CD133 positive T1 cells showed a truncation mutation in the exons 2-7 of the EGFR (EGFRvIII) gene. These results suggest that continuous expansion of neural stem cells in culture may lead to malignant spontaneous transformation. This phenomenon may be functionally related to EGFR by EGFRvIII gene mutation.     

Distinction between carcinoma cells and mesothelial cells in serous effusions. Usefulness of immunohistochemistry

The usefulness of an immunoperoxidase battery to distinguish carcinomatous from benign effusions was examined. Cell block sections from 90 previously diagnosed effusions were stained with antibodies to Leu-M1, B72.3, epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA) and vimentin. The 90 cases comprised 69 carcinomas (23 mammary, 16 ovarian, 10 pulmonary, 7 gastrointestinal [GI] and 13 others), 2 malignant mesotheliomas and 19 cases with reactive mesothelial cells only. EMA and vimentin were the most useful markers for distinguishing carcinoma cells from reactive mesothelial cells. EMA reacted with 86% of the carcinomas while vimentin reacted with 90% of the reactive cases. Leu-M1, B72.3 and CEA, although generally less sensitive than EMA, were also helpful in this regard. Additionally, the use of Leu-M1 and CEA together may help to distinguish pulmonary from GI carcinomas.     

Optimization of primary culture condition for mesenchymal stem cells derived from umbilical cord blood with factorial design

Mesenchymal stem cells (MSCs) can not only support the expansion of hematopoietic stem cells in vitro, but also alleviate complications and accelerate recovery of hematopoiesis during hematopoietic stem cell transplantation. However, it proved challenging to culture MSCs from umbilical cord blood (UCB) with a success rate of 20–30%. Many cell culture parameters contribute to this outcome and hence optimization of culture conditions is critical to increase the probability of success. In this work, fractional factorial design was applied to study the effect of cell inoculated density, combination and dose of cytokines, and presence of serum and stromal cells. The cultured UCB‐MSC‐like cells were characterized by flow cytometry and their multilineage differentiation potentials were tested. The optimal protocol was identified achieving above 90% successful outcome: 2 × 10⁶ cells/mL mononuclear cells inoculated in Iscove's modified Dulbecco's medium supplied with 10% FBS, 15 ng/mL IL‐3, and 5 ng/mL Granulocyte‐macrophage colony‐stimulating factor (GM‐CSF). Moreover, the UCB‐MSC‐like cells expressed MSC surface markers of CD13, CD29, CD105, CD166, and CD44 positively, and CD34, CD45, and human leukocyte antigens‐DR (HLA‐DR) negatively. Meanwhile, these cells could differentiate into osteoblasts, chondrocytes, and adipocytes similarly to MSCs derived from bone marrow. In conclusion, we have developed an efficient protocol for the primary culture of UCB‐MSCs by adding suitable cytokines into the culture system. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

IL-9 enhances the growth of human mast cell progenitors under stimulation with stem cell factor

We examined the effects of IL-9 on human mast cell development from CD34(+) cord blood (CB) and peripheral blood cells in serum-deprived cultures. IL-9 apparently enhanced cell production under stimulation with stem cell factor (SCF) from CD34(+) CB cells. A great majority of the cultured cells grown with SCF + IL-9 became positive for tryptase at 4 wk. In methylcellulose cultures of CD34(+) CB cells, IL-9 increased both the number and size of mast cell colonies grown with SCF. Furthermore, SCF + IL-9 caused an exclusive expansion of mast cell colony-forming cells in a 2-wk liquid culture of CD34(+) CB cells, at a level markedly greater than for SCF alone. Clonal cell cultures and RT-PCR analysis showed that the targets of SCF + IL-9 were the CD34(+)CD38(+) CB cells rather than the CD34(+)CD38(-) CB cells. IL-9 neither augmented the SCF-dependent generation of progeny nor supported the survival of 6-wk-cultured mast cells. Moreover, there was no difference in the appearance of tryptase(+) cells and histamine content in the cultured cells between SCF and SCF + IL-9. The addition of IL-9 increased numbers of mast cell colonies grown with SCF from CD34(+) peripheral blood cells in children with or without asthma. It is of interest that mast cell progenitors of asthmatic patients responded to SCF + IL-9 to a greater extent than those of normal controls. Taken together, IL-9 appears to act as a potent enhancer for the SCF-dependent growth of mast cell progenitors in humans, particularly asthmatic patients.