C-kit Staining Research Articles

Identification of Interstitial Cells of Cajal in the Rabbit Portal Vein

Abstract Two layers of interstitial cells (ICs) of Cajal were detected by c-kit and methylene blue staining in the media of the rabbit portal vein in subendothelial intramuscular and deeper intramuscular positions, displaced radially from each other by about 40–70 μm. Two morphologically distinct types of ICs were found among enzymatically dispersed cells from this vessel: small multipolar cells with stellate-shaped bodies not exceeding 20 μm, and spindle-shaped cells from 40 to 300 μm in length with numerous branching processes. Relaxed smooth muscle cells (SMCs) had a more constant length (90–150 μm). The cell membrane capacitance was 46.5±2.2 pF in SMCs, 39.7±2.4 pF in spindle-shaped ICs and 27.8±0.7 pF in multipolar ICs. Although darker under phase contrast, after loading with fluo-4 AM, single isolated ICs of both types usually had brighter fluorescence than SMCs and displayed various spontaneous calcium events, including Ca 2+ sparks and Ca 2+ waves. Ca 2+ waves were usually followed by contraction of SMCs but no change in shape of ICs. In some ICs spontaneous [Ca 2+ ] i transients (lasting about 2 s) which propagated towards the end of the processes were observed. Physical contacts between the processes of ICs and the body of one or more SMCs survived the isolation procedure. Application of noradrenaline (1–10 μM), caffeine (1–10 mM) or high-K + solution (60 mM) led to a rise of [Ca 2+ ] i in both SMCs and ICs evoking contraction of SMCs but not ICs. No differences in electrophysiological characteristics between single enzymatically isolated IC and SMC were detected; thus, the resting membrane potential estimated under current–clamp conditions was −46.5±2.0 mV in spindle-shaped ICs and −45.6±2.7 mV in SMCs. Under voltage–clamp, both ICs and SMCs revealed a well-developed voltage-gated nifedipine-sensitive L-type Ca 2+ current, a set of K + currents, including spontaneous transient outward currents (STOCs) but no Na + current. This study for the first time directly demonstrated the presence in vascular tissue of ICs. Possible roles for ICs including their involvement in spontaneous activity of the vessel were discussed.

Quantitative changes in gene expression in fetal rat testes following exposure to di(n-butyl) phthalate.

Di(n-butyl) phthalate (DBP) alters male reproductive development by decreasing testicular testosterone (T) production when fetuses are exposed on gestation days (GD) 12-21. Previous studies have shown altered gene expression for enzymes in the T biosynthetic pathway following exposure to DBP. The objectives of this study were to develop a more detailed understanding of the effect of DBP on steroidogenesis, using a robust study design with increased numbers of dams and fetuses, compared with previous studies, and to explore messenger RNA (mRNA) expression for other critical genes involved in androgen biosynthesis and signaling. Additionally, immunohistochemical localization of protein expression for several key genes was performed to further confirm mRNA changes. Fetal Leydig cell lipid levels were also examined histochemically, using oil red O. Six to seven pregnant Crl:CD(SD)BR rats per group were gavaged with corn oil or DBP at 500 mg/kg/day on GD 12-19. Testicular RNA isolated from three randomly selected GD 19 fetuses per litter was used for real-time RT-PCR for the following genes: scavenger receptor class B-1 (SRB1), steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450c17, 17beta-hydroxysteroid dehydrogenase (17beta-HSD), androgen receptor (AR), luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), stem cell factor tyrosine kinase receptor (c-kit), stem cell factor (SCF), proliferating cell nuclear antigen (PCNA), and testosterone-repressed prostate message-2 (TRPM-2). mRNA expression was downregulated for SRB1, StAR, P450scc, 3beta-HSD, P450c17, and c-kit following DBP exposure, and TRPM-2 was upregulated. 17beta-HSD, AR, LHR, FSHR, and PCNA were not significantly changed. Immunohistochemical staining for c-kit was seen in fetal Leydig cells, which has not been previously reported. Downregulation of most of the genes in the T biosynthetic pathway confirms and extends previous findings. Diminished Leydig cell lipid content and alteration of cholesterol transport genes also support altered cholesterol metabolism and transport as a potential mechanism for decreased T synthesis following exposure to DBP.

Expression of the c-kit receptor in choroidal melanomas.

The KIT gene encodes c-kit, a transmembrane receptor that has tyrosine kinase activity and plays a role in haematopoiesis, gametogenesis and melanogenesis. The c-kit protein is found in normal cutaneous and choroidal melanocytes, and there is evidence that expression is lost in melanoma. Expression of c-kit was analysed in 57 paraffin-embedded sections of choroidal melanoma specimens and three choroidal melanoma cell lines using immunochemistry and Western blotting. Of the tumour specimens, 75% stained positively for c-kit with a membrane pattern of reactivity. Of the six patients who underwent proton beam therapy before enucleation, five tumours exhibited no c-kit immunoreactivity and the other tumour demonstrated weak staining. Of the three melanoma cell lines used, c-kit expression was observed in only one. No correlations between c-kit positivity and parameters such as cell type, largest macroscopic tumour dimension, scleral invasion or pigmentation were observed. In contrast, a significant positive association was found between c-kit staining and mitotic activity (P = 0.02). However, c-kit expression did not significantly influence survival when evaluated by univariate analysis. In conclusion, c-kit is expressed in most choroidal melanoma tumours. Further analysis should provide new insights into the mechanisms underlying the molecular and cellular changes in choroidal melanomas.

Identification of interstitial cells of Cajal in the rabbit portal vein

Two layers of interstitial cells (ICs) of Cajal were detected by c-kit and methylene blue staining in the media of the rabbit portal vein in subendothelial intramuscular and deeper intramuscular positions, displaced radially from each other by about 40–70 μm. Two morphologically distinct types of ICs were found among enzymatically dispersed cells from this vessel: small multipolar cells with stellate-shaped bodies not exceeding 20 μm, and spindle-shaped cells from 40 to 300 μm in length with numerous branching processes. Relaxed smooth muscle cells (SMCs) had a more constant length (90–150 μm). The cell membrane capacitance was 46.5±2.2 pF in SMCs, 39.7±2.4 pF in spindle-shaped ICs and 27.8±0.7 pF in multipolar ICs. Although darker under phase contrast, after loading with fluo-4 AM, single isolated ICs of both types usually had brighter fluorescence than SMCs and displayed various spontaneous calcium events, including Ca 2+ sparks and Ca 2+ waves. Ca 2+ waves were usually followed by contraction of SMCs but no change in shape of ICs. In some ICs spontaneous [Ca 2+] i transients (lasting about 2 s) which propagated towards the end of the processes were observed. Physical contacts between the processes of ICs and the body of one or more SMCs survived the isolation procedure. Application of noradrenaline (1–10 μM), caffeine (1–10 mM) or high-K + solution (60 mM) led to a rise of [Ca 2+] i in both SMCs and ICs evoking contraction of SMCs but not ICs. No differences in electrophysiological characteristics between single enzymatically isolated IC and SMC were detected; thus, the resting membrane potential estimated under current–clamp conditions was −46.5±2.0 mV in spindle-shaped ICs and −45.6±2.7 mV in SMCs. Under voltage–clamp, both ICs and SMCs revealed a well-developed voltage-gated nifedipine-sensitive L-type Ca 2+ current, a set of K + currents, including spontaneous transient outward currents (STOCs) but no Na + current. This study for the first time directly demonstrated the presence in vascular tissue of ICs. Possible roles for ICs including their involvement in spontaneous activity of the vessel were discussed.

Identification of c-kit-positive cells in the mouse ureter: the interstitial cells of Cajal of the urinary tract.

The existence of a pacemaker system in the urinary tract capable of orchestrating the movement of filtrated urine from the ureteral pelvis to the distal ureter and lower urinary tract seems intuitive. The coordinated activity necessary for such movement or "peristalsis" would likely require an intricate network of cells with pacemaker-like activity, as is the case with the interstitial cells of Cajal (ICC) of the gut. We investigated whether these putative pacemaker cells of the urinary tract are antigenically similar to ICC of the gut by using immunofluorescence staining for c-kit, a cell-surface marker specific for ICC. Ureteral, urinary bladder, and urethral tissues were harvested from female mice of the WBB6F1 strain, and fixed sections were prepared and stained for c-kit. Cell networks composed of stellate-appearing, c-kit-positive, ICC-like cells were found in the lamina propria and at the interface of the inner longitudinal and outer circular muscle layers of the ureteral pelvis but not in the urinary bladder or urethra. Thus, like in the gut, c-kit-positive, ICC-like cells are present in the urinary tract but appear to be restricted to the proximal ureter of this murine species.

Mast cell tumors of the gastrointestinal tract in 39 dogs.

Mast cell tumors (MCTs) of gastrointestinal origin that had been surgically removed from 39 dogs were examined to evaluate their pathologic features. Miniature breeds, especially Maltese, were most frequently affected. The average age of affected dogs was 9.7 +/- 2.6 years. No sex difference was apparent. The most frequently affected sites were in the upper digestive tract, and the prognosis was very poor. Grossly, the gastrointestinal wall was prominently thickened, and the lumen of the affected gut was usually narrowed. Microscopically, there was diffuse transmural invasion of round to pleomorphic tumor cells. Tumor cells had moderate to abundant cytoplasm, round to ovoid nuclei with scattered chromatin, and mitotic figures. Fibrous stroma was observed in about half of the tumors. There was variable infiltration of eosinophils. In all tumors, cytoplasmic granules showed weak metachromasia, but the number of granules was very small. Immunohistochemical staining for c-kit and mast cell tryptase was positive in 77% and 62% of tumors, respectively. All tumors were positive for at least two of these markers. Immunohistochemical staining for p53 was positive in 13% of the tumors. Reactivity for staining markers and p53 was unrelated to cell pleomorphism, vessel invasion, or survival time. Gastrointestinal MCTs have histologic and immunohistochemical features completely different from those of other primary or metastatic gastrointestinal tumors. The combination of immunostaining for mast cell tryptase and c-kit and histochemical staining for metachromasia appears to be a powerful tool for the diagnosis of gastrointestinal MCTs.

Immunohistochemical Staining for c-Kit (CD117) Is a Rare Event in Human Colorectal Carcinoma

Recent studies have suggested that the presence of a c-Kit/c-Kit ligand autocrine loop may be an important regulator of proliferation and progression of human colorectal cancer, capable of affecting the prognosis of these patients. If present, the c-Kit alteration may provide a suitable target for therapy, similar to what has been observed in gastrointestinal stromal tumors. To determine the incidence of c-Kit expression in human colorectal carcinomas, we studied the immunohistochemical c-Kit expression in a selection of 126 colorectal carcinomas of different stage, using stage-oriented human cancer tissue microarrays. Formalin-fixed, paraffin-embedded tissues of each case were immunostained using the avidin-biotin-peroxidase method and the antihuman c-Kit (CD117) rabbit polyclonal antibody. High cytoplasmic c-Kit staining (Allred score of 7–8) was observed in 1.6% of the colon carcinoma patients evaluated. The c-Kit—positive tumors were poorly differentiated carcinomas arising at the anorectal junction. The remaining tumors revealed no detectable expression of c-Kit. Twenty-seven non-neoplastic tissues, normal colonic mucosa, and adenomas were also CD117 negative. We show the rare expression of c-Kit in normal and neoplastic colorectal tissues, suggesting that routine screening for c-Kit by immunohistochemistry to identify c-Kit—positive carcinomas may be cost ineffective. However, further study of c-Kit expression in poorly differentiated colon cancers may be useful since these generally chemoresistant tumors may respond to therapy with inhibitor compounds directed against c-Kit.

C-kit expression in pediatric solid tumors: a comparative immunohistochemical study.

The stem cell factor/c-kit tyrosine kinase receptor pathway has been shown to be important for tumor growth and progression in several cancers, including mast cell diseases, gastrointestinal stromal tumor, acute myeloid leukemia, small cell lung carcinoma, and Ewing sarcoma. Studies using the oral agent STI-571 (Gleevec, Novartis), an inhibitor of the tyrosine kinases bcr-abl, c-kit, and PDGFR, have shown significant responses in patients with chronic myelogenous leukemia and gastrointestinal stromal tumor. With the aim of identifying additional groups of tumors that may use the stem cell factor/c-kit pathway and secondarily may be responsive to STI-571 treatment, this study surveyed 151 primary tumors from patients treated at St. Jude Children's Research Hospital for immunohistochemical expression of c-kit. Formalin-fixed, paraffin-embedded sections were stained with rabbit polyclonal anti-human c-kit (CD117, Dako) using standard avidin-biotin-peroxidase complex technique, antigen retrieval, and an automated stainer. Strong, diffuse staining for c-kit was seen in a proportion of synovial sarcomas, osteosarcomas, and Ewing sarcomas. Strong, diffuse staining was less common in neuroblastomas, Wilms' tumors, and rhabdomyosarcomas and was negative in alveolar soft part sarcomas and desmoplastic small round cell tumors. Tumors with strong, diffuse staining for c-kit in a pattern similar to gastrointestinal stromal tumor may represent suitable targets for new therapeutic agents.

Spermatogenesis in the golden hamster: the role of c-kit.

c-kit is related to the family of transmembrane tyrosine kinase receptors. Mutations in genes for either c-kit or its ligand, Steel factor, result in infertility, but the role of c-kit/SCF system in spermatogenesis is not well understood. In this study Western blot analysis together with confocal microscopy were used to follow c-kit expression in hamsters during the first spermatogenic wave in mature animals and in old age. Three antibodies raised against different domains of c-kit were tested on Western Blot. Confocal microscopy was performed after incubation of fixed seminiferous tubules with tested antibodies followed by binding of FITC-labeled secondary antibody. Longitudinal sections of seminiferous tubule were observed by confocal microscopy to determine in which stages of spermatogenesis and in which cell types c-kit was found. C-kit bands of 80,140, and 150 kDa were observed on Western blot, indicating that c-kit is a name related to several proteins sharing some common domains. Only the band of 150 kDa correlated with positive staining of c-kit in tubules using confocal microscopy. We term this protein c-kit150T (150 kDa, testis). We demonstrated that c-kit150T appeared in differentiating hamster spermatogonia at stages VII-VIII of adult spermatogenesis and at day 13-14 during the first spermatogenic wave. It remained attached to the cell until late pachytene. This suggests that c-kit may play a role in preparing the germinal cells to enter meiosis. In order to evaluate the effect of aging on the number of germ cells, B2 spermatogonia/Sertoli cell ratio was calculated in the group of young animals (5-7 months) compared to this ratio in older ones (20-26 months). A significant decrease (P < 0.01) in the number of B2 spermatogonia in the group of old hamsters as compared to young ones was seen. The calculated value for the B2 spermatogonia/Sertoli cell ratio was 5.6 +/- 0.7 in young animals and 3.8 +/- 1.2 in the 20-26 months ones. In addition, decrease in the intensity of staining for c-kit was detected in the old hamsters. These may be the reasons for subfertility in old age and in other cases of testicular disorders.

False-negative Biopsy for Testicular Intraepithelial Neoplasia and High-risk Features for Testicular Cancer

The purpose of this report is to emphasize the possibility of false-negative biopsies for testicular intraepithelial neoplasia (TIN) in men with high-risk features of testicular cancer and to review the relevant literature. At the Norwegian Radium Hospital patients in this category are offered the chance to undergo a testicular biopsy. A patient is described who had a normal testicular biopsy a decade before presenting with an invasive testicular cancer. Furthermore, this patient is the first case reported with a false-negative biopsy for TIN and a family history of testicular cancer. The evaluation of the biopsies included immunohistochemical staining for c-kit and PlAP (placental-like alkaline phosphatase) in order to diagnose early TIN. Though multifocal or diffuse extension seems to be the most frequent pattern of distribution of TIN, the presented case and another 14 cases from the literature review indicate that the focality of TIN may be a reason for a TIN-negative biopsy.

Heme oxygenase-2 distribution in anorectum: colocalization with neuronal nitric oxide synthase

Recent investigations have suggested carbon monoxide (CO) as a putative messenger molecule. Although several studies have implicated the heme oxygenase (HO) pathway, responsible for the endogenous production of CO, in the neuromodulatory control of the internal anal sphincter (IAS), its exact role is not known. Nitric oxide, produced by neuronal nitric oxide synthase (nNOS) of myenteric neurons, is an important inhibitory neural messenger molecule mediating nonadrenergic noncholinergic (NANC) relaxation of the IAS. The present studies were undertaken to investigate in detail the presence and coexistence of heme oxygenase-2 (HO-2) with nNOS in the opossum anorectum. In perfusion-fixed, frozen-sectioned tissue, HO-2 immunoreactive (IR) and nNOS IR nerves were identified using immunocytochemistry. Ganglia containing HO-2 IR neuronal cell bodies were present in the myenteric and submucosal plexuses throughout the entire anorectum. Colocalization of HO-2 IR and nNOS IR was nearly 100% in the IAS and decreased proximally from the anal verge. In the rectum, colocalization of HO-2 IR and nNOS IR was approximately 70%. Additional confocal microscopy studies using c-Kit staining demonstrated the localization of HO-2 IR and nNOS IR in interstitial cells of Cajal (ICC) of the anorectum. From the high rate of colocalization of HO-2 IR and nNOS IR in the IAS as well as the localization of HO-2 IR and nNOS IR in ICC in conjunction with earlier studies of the HO pathway, we speculate an interaction between HO and NOS pathways in the NANC inhibitory neurotransmission of the IAS and rectum.

Expression of the stem cell factor receptor c-kit in normal and diseased pediatric liver: identification of a human hepatic progenitor cell?

The stem cell factor (SCF)/c-kit ligand/receptor system has been implicated in stem (oval) cell activation following liver injury in the rat. The aim of this study was to determine the role of the SCF/c-kit system in pediatric human liver during acute and chronic liver injury. Tissue was obtained from hepatectomy specimens of patients undergoing liver transplantation for extrahepatic biliary atresia (EHBA) and fulminant hepatic failure (FHF). Specific expression of mRNA for c-kit and beta-actin was measured by ribonuclease protection and by immunohistochemistry to localize c-kit in tissue sections. Expression of c-kit was detected at relatively consistent levels in normal and cirrhotic (EHBA) livers. However, in FHF, c-kit mRNA levels were elevated in 3 of 6 specimens. Immunolocalization highlighted the presence of small numbers of c-kit-positive cells in the portal tracts of normal livers with increased numbers in cirrhotic livers. The highest c-kit staining, however, was observed in FHF, in which, in addition to the cells in the portal tracts, discrete c-kit-positive cells were also found integrated into bile ducts. Colocalization studies demonstrated some of the c-kit-positive cells to be of mast cell, leukocyte, and hematopoietic cell origin. However, there remained a subset that was also negative for these markers. The up-regulation of c-kit receptor expression in diseased livers suggests an involvement of this receptor/ligand system in hepatic repair mechanisms, and we speculate that c-kit-positive cells may represent a hepatic progenitor cell population. The origin and growth/differentiation potential of these c-kit-positive cells is under investigation.

Human conjunctival mast cells: expression of Fc epsilonRI, c-kit, ICAM-1, and IgE.

To characterize the expression and regulation of conjunctival mast cell surface receptors important in allergic inflammation. Mast cells were isolated from human conjunctival tissues of cadavers. Mast cell surface markers were identified using flow cytometry with antibodies to IgE, Fc epsilonRI, c-kit, and intercellular adhesion molecule-1 (ICAM-1). We evaluated the effect of 24-hour tumor necrosis factor alpha (TNF-alpha) or interleukin 4 (IL-4) incubation on the expression of mast cell c-kit, ICAM-1, and surface-bound IgE. Staining of mast cells (c-kit and/or tryptase positive) yielded positive results for all of the variables measured. The intensity of mast cell c-kit staining increased with TNF-alpha incubation, but decreased below that of unstimulated mast cells when incubated with IL-4. Anti-ICAM-1 and anti-IgE staining were increased over that of unstimulated cells when incubated with TNF-alpha or IL-4. In this model, TNF-alpha up-regulates mast cell surface receptors and cell-bound IgE. Interleukin 4 up-regulates mast cell ICAM-1 and cell-bound IgE, but down-regulates c-kit. Conjunctival mast cells play a critical role in the pathogenesis of atopic ocular disease. Characterization of the expression and regulation of mast cell surface receptors is important to the development of potential novel treatments for ocular inflammation.

The expression of thec-kitreceptor by epidermal melanocytes may be reduced in vitiligo

The proto-oncogene c-kit encodes the transmembrane tyrosine kinase receptor that has a role in the growth regulation of various cell types including melanocytes. In the present study we have examined the expression of the c-kit protein in the skin of seven patients with vitiligo. Melanocytes positive for c-kit protein were observed in the basal layer in non-lesional skin and the mean number of 25.8 +/- 5.2 (per 200 basal cells) compared with that of 21.8 +/- 3.5 from six control subjects. In perilesional skin there was a reduction in the numbers of c-kit positive melanocytes (6.7 +/- 2.6) and this was especially noticeable in six of the seven patients. Such a reduction was less obvious following staining with MEL-5 and in only two subjects were the numbers of melanocytes below the normal range. This suggests that the reduction in c-kit staining was the result of decreased expression of the protein rather than a loss of melanocytes. No melanocytes, positive for c-kit protein, or after staining with MEL-5, were identified in lesional skin although isolated tyrosinase-positive melanocytes were seen in one subject. There was no apparent change in the numbers of mast cells expressing c-kit protein and the intensity of staining in the dermis even in lesional skin was similar to that in the controls. These results demonstrate that c-kit protein is present on melanocytes in adult human skin and that in perilesional skin of some vitiligo patients there is a reduction in the numbers of melanocytes expressing this receptor. Whether this may contribute to the defective melanocyte growth and/or survival that occurs in vitiligo or whether it is a consequence of melanocyte damage remains to be seen.

Expression of Stem Cell Factor and Its Receptor by Human Neuroblastoma Cells and Tumors

Bone marrow (BM) is a frequent site of metastasis in children with neuroblastoma (NB). Nonhematopoietic cell lines of the same neuroectodermal origin produce both stem cell factor (SCF) and its receptor, the product of the c-kit protooncogene (c-kit). Because recombinant SCF is likely to be soon clinically tested to accelerate BM recovery after high-dose chemotherapy, a treatment administered to children with disseminated NB, we addressed the question of whether SCF/c-kit complex could play a role in the proliferation and metastasis of NB cells. Northern blot analysis showed SCF mRNA transcripts in 7 of 8 (88%) NB cell lines and c-kit in 1 (13%). Neither c-kit nor SCF could be detected by Western blotting in cell extracts or by surface immunofluorescence and flow cytometry. Soluble SCF protein was detected by enzyme immunoassay at low concentrations in the cell supernatants in the same 7 NB cell lines. Treatment of 4 NB cell lines by SCF +/- cytokines relevant to BM physiology did not induce c-kit antigenic expression or modulate 3H-thymidine uptake. Likewise, the latter was not changed by incubating the cells with anti-c-kit neutralizing antibodies. Immunohistochemical analysis showed weak diffuse or focal staining for SCF and c-kit in few primary or metastatic tumor samples, only once simultaneously. We conclude that NB cell lines usually produce low levels of soluble SCF but do not express c-kit and that both proteins are rarely detected in NB tumors. The SCF/c-kit complex appears to be unlikely to stimulate NB growth or metastasis; thus, recombinant SCF could be safely administered to children with NB.

Expression of stem cell factor and its receptor by human neuroblastoma cells and tumors

Bone marrow (BM) is a frequent site of metastasis in children with neuroblastoma (NB). Nonhematopoietic cell lines of the same neuroectodermal origin produce both stem cell factor (SCF) and its receptor, the product of the c-kit protooncogene (c-kit). Because recombinant SCF is likely to be soon clinically tested to accelerate BM recovery after high-dose chemotherapy, a treatment administered to children with disseminated NB, we addressed the question of whether SCF/c-kit complex could play a role in the proliferation and metastasis of NB cells. Northern blot analysis showed SCF mRNA transcripts in 7 of 8 (88%) NB cell lines and c-kit in 1 (13%). Neither c-kit nor SCF could be detected by Western blotting in cell extracts or by surface immunofluorescence and flow cytometry. Soluble SCF protein was detected by enzyme immunoassay at low concentrations in the cell supernatants in the same 7 NB cell lines. Treatment of 4 NB cell lines by SCF +/- cytokines relevant to BM physiology did not induce c-kit antigenic expression or modulate 3H-thymidine uptake. Likewise, the latter was not changed by incubating the cells with anti-c-kit neutralizing antibodies. Immunohistochemical analysis showed weak diffuse or focal staining for SCF and c-kit in few primary or metastatic tumor samples, only once simultaneously. We conclude that NB cell lines usually produce low levels of soluble SCF but do not express c-kit and that both proteins are rarely detected in NB tumors. The SCF/c-kit complex appears to be unlikely to stimulate NB growth or metastasis; thus, recombinant SCF could be safely administered to children with NB.