Biphosphonates-associated osteonecrosis of the jaw: the role of gene-environment interaction.

Biphosphonate (BPN) are widely used in clinics to treat metastatic cancer and osteoporosis thus representing a problem not only for patients but also for workers involved in their preparation and administration. A similar exposure occurred years ago in match-making workers undergoing bone alterations similar to those consequent to BPN exposure. Osteonecrosis of the jaw (ONJ) is a main adverse effect related to BPN administration, which is performed in millions of patients worldwide for osteoporosis and cancer therapy, thus representing an emerging problem in public health. In susceptible patients, BPN induce severe, progressive, and irreversible degeneration of facial bones, resulting in avascular ONJ often triggered by dental surgery. BPN induced ONJ occurs in subjects depending on lifestyle factors of both environmental and endogenous origins. Exogenous risk factors include cigarette smoke, alcohol consumption, bacterial infections, and cyclosporine therapy. Endogenous risk factors include systemic diseases such as diabetes or hypertension and adverse polymorphisms of genes involved in metabolism (CYPs, MTHFR), thrombosis (Factor V, Prothrombin), and detoxification (MDR). Available molecular findings provide evidence that ONJ is related to risk-factors associated with environmental mutagenesis and gene-environment interactions. This issues may be useful to identify susceptible subjects by molecular analyses in order to prevent ONJ occurrence.

No improvement of survival with reduced- versus high-intensity conditioning for allogeneic stem cell transplants in Ewing tumor patients.

BACKGROUND: Outcomes of Ewing tumor (ET) patients treated with allogeneic stem cell transplantation (allo-SCT) were compared regarding the use of reduced-intensity conditioning (RIC) and high-intensity conditioning (HIC) regimens as well as human leukocyte antigen (HLA)-matched and HLA-mismatched grafts. PATIENTS AND METHODS: We retrospectively analyzed data of 87 ET patients from the European Group for Blood and Marrow Transplantation, Pediatric Registry for Stem Cell Transplantations, Asia Pacific Blood and Marrow Transplantation and MetaEICESS registries treated with allo-SCT. Fifty patients received RIC (group A) and 37 patients received HIC (group B). Twenty-four patients received HLA-mismatched grafts and 63 received HLA-matched grafts. RESULTS: Median overall survival was 7.9 months [±1.24, 95% confidence interval (CI) 5.44-10.31] for group A and 4.4 months (±1.06, 95% CI 2.29-6.43) for group B patients (P = 1.3). Death of complications (DOC) occurred in 4 of 50 (0.08) and death of disease (DOD) in 33 of 50 (0.66) group A and in 16 of 37 (0.43) and 17 of 37 (0.46) group B patients, respectively. DOC incidence was decreased (P < 0.01) and DOD/relapse increased (P < 0.01) in group A compared with group B. HLA mismatch was not generally associated with graft-versus-Ewing tumor effect (GvETE). CONCLUSIONS: There was no improvement of survival with RIC compared with HIC due to increased DOD/relapse incidence after RIC despite less DOC incidence. This implicates general absence of a clinically relevant GvETE with current protocols.

Fabrication of chitosan-coated porous polycaprolactone/strontium-substituted bioactive glass nanocomposite scaffold for bone tissue engineering.

In the present study, porous (about 70 vol%) nanocomposite scaffolds made of polycaprolactone (PCL) and different amounts (0 to 15 wt%) of 45S bioactive glass (BG) nanoparticles (with a particle size of about 40 nm) containing 7 wt% strontium (Sr) were fabricated by solvent casting technique for bone tissue engineering. Then, a selected optimum scaffold was coated with a thin layer of chitosan containing 15 wt% Sr-substituted BG nanoparticles. Several techniques such as X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), tensile test, and water contact angle measurement were used to characterize the fabricated samples. In vitro experiments including degradation, bioactivity, and biocompatibility (i.e., cytotoxicity, alkaline phosphate activity, and cell adhesion) tests of the fabricated scaffold were performed. The biomedical behavior of the fabricated PCL-based composite scaffold was interpreted by considering the presence of the porosity, Sr-substituted BG nanoparticles, and the chitosan coating. In conclusion, the fabricated chitosan-coated porous PCL/BG nanocomposite containing 15 wt% BG nanoparticles could be utilized as a good candidate for bone tissue engineering.

Psychoactive drug consumption among truck-drivers: a systematic review of the literature with meta-analysis and meta-regression.

Few studies have assessed the extent of psychoactive drug consumption in the occupational setting. The trucking sector, in particular, is an important cause for concern, since psychoactive substance use has a relevant impact on the drivers' health and safety, increasing the risk of injuries and traffic accidents, potentially affecting the general public health as well. A systematic review of the literature and meta-analysis was performed in order to provide Occupational Health Professionals and policy-makers with an updated epidemiological perspective regarding this important issue. The results showed a prevalence of overall drug consumption of 27.6% [95%CI 17.8-40.1], particularly high considering illicit CNS-stimulants (amphetamine consumption of 21.3% [95%CI 15.7-28.1], and cocaine consumption of 2.2% [95%CI 1.2-4.1]). It appears that truck-drivers choose stimulant substances as a form of performance enhancing drug, in order to increase productivity. However, chronic and high dose consumption has been shown to decrease driving skills, placing these professional drivers at risk for health and road safety. Further research is required, particularly in Europe, in order to fill the knowledge gap and improve the strength of evidence.

Long-term persistency of hepatitis B immunity: an observational cross-sectional study on medical students and resident doctors.

Hepatitis B virus (HBV) is a main cause of chronic and acute hepatitis. Healthcare workers (HCWs), including medical students and resident doctors, have an occupational risk of HBV infection. The study aimed to evaluate the long-term persistence of protective anti-HBs antibody levels in healthcare students and resident doctors at risk for occupational exposure to HBV at 15 years after primary vaccination course. Further objective was to evaluate the anamnestic response observed in non-seroprotected subjects receiving a booster dose. Data were collected from the clinical documentation filled in during the occupational medical check of medical students and resident doctors undergoing Occupational Health Surveillance by the University of Ferrara. Of the 621 included individuals, 27.7% had an anti-HBs concentration < 10 mIU/mL. Subjects vaccinated during infancy had more frequently a concentration < 10 mIU/mL than those vaccinated during adolescence (42.7% vs 6.9%; p-value < 0.001). Multivariate analysis confirmed the statistical significance of the vaccination age. 94 subjects who had an anti-HBs concentration < 10 mIU/mL received a booster dose. The proportion of subjects who had an anamnestic response was higher in those vaccinated in infancy rather than during adolescence (94.1% vs 77.8% respectively). These findings suggest that the anti-HBs concentration decreases below 10 mIU/mL more frequently in subjects vaccinated during infancy. Immunological memory seems to persist after the decline of the anti-HB titer, as observed in response to a booster dose. In conclusion, vaccinated subjects at increased risk of HBV infection should be monitored and a booster dose administered if anti-HBs titer is below 10 mIU/mL.

SCT for Wilms' tumour.

Thanks to advances in treatment, approximately 85-90% of patients suffering from Wilms' tumour are now cured. However, success rate after relapse is significantly lower, ranging from 25 to 45%. Several different re-induction approaches, more or less intensive according to first-line therapy and characteristics of relapse, have been proposed. A number of adverse prognostic factors related to a bad outcome after relapse have been identified and are used as inclusion criteria for entering in a programme including high-dose chemotherapy (HCT). HCT followed by autologous haematopoietic stem cell rescue has been used in small numbers of patients worldwide and promising results have been reported. Information from the European Group for Blood and Marrow Transplantation Database regarding more than 300 transplants have been gathered. In addition, literature data on rescue therapy and HCT will be discussed, such as recent treatment proposals currently under discussion within European and US cooperative groups.

Early complications following haematopoietic SCT in children.

Early complications can be defined as those occurring within 100 days after transplant. Both epithelial and endothelial damage represent the pathogenetic basis for the onset of the most frequent complications. Clinical features related to endothelial damage depend on the involved district or on the grade and type of general distribution. Veno-occlusive disease (VOD) most often occurs within the first 20 days of haematopoietic SCT (HSCT) and is characterized by the obstruction of small intrahepatic venules and is caused by an initial injury of the sinusoid endothelial cells. The incidence in children ranges between 27 and 40%, and symptoms include hepatomegaly, portal hypertension and ascites. Early intervention with defibrotide (DF) proved to be effective for the treatment; however, overall mortality ranges between 20 and 50%. Thrombotic microangiopathy (TAM) incidence is 4-13%. It is often associated with the use of CYA or tacrolimus, and symptoms include haemolytic anaemia, thrombocytopenia and renal and/or central nervous system impairment. Treatment includes plasmapheresis and supportive care. The promising role of DF needs to be confirmed. The onset of engraftment syndrome may occur 1 or 2 days before the neutrophil count in peripheral blood increases. Clinical symptoms include fever not related to infection, respiratory involvement with pulmonary infiltrates or hypoxia and skin rash. Treatment consists of steroid administration for a few days. Haemorrhagic cystitis (HC) may occur early or later following transplant. Early-onset HC is related to mucosal damage caused by the catabolites of chemotherapy drugs, and late-onset HC is mostly caused by viral infections. The incidence ranges between 1 and 25%. Clinical symptoms include haematuria and dysuria without infections. Treatment includes hyperhydration and platelet support. In case of vescical clots, bladder irrigation is indicated. In advanced cases, hyperbaric oxygen administration or surgery may be useful. The use of cidofovir for BK virus-related HC seems encouraging, but further studies are needed to confirm its real efficacy.

Non-endocrine late complications in children after allogeneic haematopoietic SCT.

Non-endocrine events represent a heterogeneous group of complications occurring in children who survive long term after haematopoietic SCT. This review highlights the late sequel in a growing child. The preparative regimen itself with high-dose chemotherapy and/or radiotherapy (TBI) or the treatment given before the transplant procedure may cause organ damage with permanent sequel. Immune reconstitution and chronic GvHD have crucial role in occurrence of clinical abnormalities and late severe infections. Autoimmune syndromes may occur after use of novel transplant modalities (cord blood transplantation, reduced intensity conditioning regimen and haploidentical T-cell-depleted SCTs). Exposure to chemo- and/or radiotherapy increases the risk of second malignant neoplasms. Surveillance strategy focusing on each potential complication risk at continuous follow-up will allow vigilant post transplant care. Each paediatrician must be well versed in appropriate monitoring of these complications. Guidelines and recommendations are provided for serious problems occurring at follow-up, which must rapidly be identified so that appropriate intervention can be initiated. To achieve cure at a lowest possible price in terms of suffering and cost expenditures for health care is an extended frontier of paediatric haematopoietic SCT and biggest challenge for a paediatrician.

Strategies of the donor search for children with second CR ALL lacking a matched sibling donor.

During the last 10 years, the number of alternative Haematopoietic stem cell transplantations (HSCTs) performed on children in Europe has increased significantly and has reached 61% of the allografts. In this paper, we provide practical guidelines to help define an algorithm for the treatment of children relapsing during or after first-line chemotherapy for ALL and lacking a matched sibling donor. A simultaneous search for an unrelated donor and for a cord blood unit should be started. This study focuses mainly on the effects of some factors on survival in an effort to highlight the influence that these factors have on our choices. Matching the patient for HLA-A, -B, -C and -DRB1 alleles remains the top priority: a single HLA class I or II allele mismatch has no influence on survival, while multiple mismatching for more than one class I allele and simultaneous disparities in class I and II alleles increase mortality. The impact of additional mismatches for HLA-DQ and -DP loci on survival is still controversial. Young donor age is the most important factor that has a significant effect on better survival from among several other factors, including CMV sero-status, gender and ABO. An 18- to 30-year-old, 8/8 allele-matched donor (excluding allele matching at DQB1) or for many teams 10/10 allele-matched donor; or a 4 out of 6 (considering Ag HLA-A, -B and allelic typing of DRB1) CB unit containing more than 3.0 x 10(7) nuclear cells is considered by most institutions. The choice should be made on the basis of urgency. If a donor or a CB unit is not found within an appropriate time frame, generally less than 3 months after obtention of remission, haploidentical HSCT should be offered. Some institutions consider haploidentical HSCT the second therapeutic option when a matched donor is not available.

Endocrinological late complications after hematopoietic SCT in children.

The main challenge for a pediatric hemato-oncologist today is to obtain a cure for the sick child with the minimum of treatment-related complications. Children on their way to achieving adulthood face many risks after hematopoietic SCT (HSCT). Continuous follow-up includes assessment of organ function, focus on vaccinations and screening for secondary malignancies. Updated treatment protocols are already adjusted according to the knowledge obtained on late effects, and the potential risks for complications are well balanced with expected benefits hopefully resulting in decreased potential risk for organ damage but still maintaining an unchanged or improved survival rate. Recent developments on pre-HSCT regimens, such as the introduction of new anticancer regimens and immunosuppressive agents will hopefully contribute to minimize the frequency and the severity of late complications. Knowledge about increased risk for long-term complications due to cancer therapy and pre-HSCT preparative regimens should encourage each caring physician to stick to follow-up protocols and treatment guidelines not only to improve the survival rate of transplanted children but also to improve their quality of life. To achieve adulthood by maintaining cognitive ability and psychosocial skills is the highest goal for an individual to become a competent member of a society. This review of late endocrine complications after HSCT focuses on growth, pubertal development, thyroid disorders and glucose metabolism in long-term survivors.

Prevention and treatment of acute GvHD.

GvHD remains a source of significant morbidity and mortality in the setting of allogeneic haematopoietic SCT. Improving outcomes in stem cell transplant recipients requires additional therapeutic modalities for GvHD, especially for patients who fail to respond to initial therapy with steroids. Moreover, while the absence of acute GvHD (aGvHD) is associated with a higher risk of relapse of the underlying malignant disease, severe aGvHD usually induces the occurrence of life-threatening complications such as severe infections. This article summarizes the current state of aGvHD prophylaxis and treatment.

Bacteremias in children receiving hemopoietic SCT.

The incidence of bacteremia following hemopoietic SCT (HSCT) changes over time from the procedure. The first 30 days have the highest incidence, both in autologous and allogeneic HSCT recipients. In the following periods, bacteremia is a frequent complication in allogeneic HSCT, especially from alternative donors. Gram-positive cocci represent the most frequent cause of single-agent bacteremia. Knowledge of epidemiology (incidence and etiology) of bacteremias following HSCT is pivotal for planning management strategies (prevention, diagnosis and therapy) that must be distinct in the different post-transplant period.

28 years of high-dose therapy and SCT for neuroblastoma in Europe: lessons from more than 4000 procedures.

Between 1978 and 2006, the European Group for Blood and Marrow Transplantation registered 4098 high-dose therapy (HDT) procedures followed by stem cell rescue (SCR) (3974 autologous/124 allogeneic) in patients with neuroblastoma. The 5-year rates for overall (OS) and event-free survival are 37 and 32%, respectively. The median age at diagnosis is 3.9 years (0.3-62 years) with 76 patients older than 18 years. Patients above 10 years carry a 2.5-fold higher risk. Younger patients cure significantly (<0.001) better with OS rates of 40 and 30% for age groups 2-4 years and 4-10 years, respectively. Their risks are about twofold higher than that of patients below 2 years with OS rates of 60%. The better the quality of remission status before HDT/SCT the better are the observed OS rates: 43% in CR1 (1199 patients) and 42% for CR2 (140 patients), and 36% for those in very good partial or partial remission (1413 patients) and 21% for those with sensitive relapse (134 patients). Patients reported with stable disease in first remission still had an OS rate of 30%. Multivariate analysis shows significantly better OS in the age group of less than 2 years (<0.0001), as well as a better quality of remission status before HDT/SCT (P<0.0001), with the use of peripheral stem cells (P=0.014), autologous SCT (P=0.031) and busulphan/melphalan HDT (P<0.001). Busulphan/melphalan HDT/SCT in first remission achieves an OS of 48%, while it is only 35% with other regimens (P<0.001), including melphalan alone, other melphalan-containing regimens, a variety of other drugs given as a single HDT as well as the addition of TBI or sequential HDT/SCT procedures. Further progress in the field may only be expected from large-scale international randomized trials.

Rare viral infections in children receiving hemopoietic stem cell transplant.

Viral infections are a rare complication in autologous hemopoietic stem cell transplant (HSCT) recipients but represent a frequent cause of disease after allogeneic HSCT. In the last years, there has been an increase in the number of viral diseases observed in these patients. This fact may be at least partially due to an improvement in diagnostic facilities, but the increasing number of transplant procedures and the more severe immunosuppression may also have played an important role.

Invasive mycoses in children receiving hemopoietic SCT.

Invasive mycoses represent a rare but severe complication following hemopoietic SCT (HSCT) in children. Their incidence is related to the type of donor, being higher after allogeneic transplant, especially from alternative donors. Moreover, the incidence of invasive mycoses varies in the different post transplant phases. Neutropenia, lymphopenia, GvHD, high-dose steroids or other immunosuppressive drugs represent well-known risk factors. The clinical features of invasive mycoses after HSCT in children are similar to those observed in adults, and the diagnostic tools, including Aspergillus galactomannan antigen detection, are feasible also in pediatrics. Mortality due to invasive mycoses after HSCT in children is high.

Haematopoietic stem cell transplantation in children in eastern European countries 1985-2004: development, recent activity and role of the EBMT/ESH Outreach Programme.

The paediatric population of 19 eastern European countries amounts to approximately 80 million children. Between 1985 and 2004, the number of centres performing haematopoietic stem cell transplantation (HSCT) in children increased from 1 in 1985 to 24 in 2004 and the yearly number of paediatric HSCTs rose from 1 in 1985 to 291 in 2004. Altogether, 2342 transplants were reported to the EBMT Registry during this time (Poland 953, Czech Republic 501, Hungary 269, Russia 217, Croatia 129, Slovakia 71, Bulgaria 45, Serbia and Montenegro 36, Slovenia 35, Belarus 33, Estonia 26, Lithuania 19 and Romania 8). Out of the 2342 transplants, 1487 (63.5%) transplants were performed in paediatric centres, 453 (19.3%) in centres for adults and 402 (17.2%) in combined centres. The number of children who underwent autologous HSCT (auto-HSCT) was 1053 (45%), whereas 1289 (55%) underwent allogeneic HSCT (allo-HSCT). Peripheral blood (PB) was the source of HSC in 751 (71.3%) out of 1053 auto-transplants, BM in 246 (23.4%) and PB+BM in 52 (4.9%) (missing data in 4, that is, 0.4%). Among the 1289 allo-transplants, BM was the source of HSC in 827 (64.3%), PB in 416 (32.3%), CB in 23 (1.8%) and BM+PB in 14 (1.1%) (missing data in 9, that is, 0.7%). Among them, 728 (57.4%) obtained HSC from MSD, 322 (25.4%) from UD, 195 (15.4%) from MMFD, 14 (1.1%) from CB family donor and 9 (0.7%) from CB unrelated donor (missing data in 21, that is, 1.6%). The number of children who underwent allo-HSCT for malignant diseases was 945 (73.4%), including ALL 376 (29.2%), AML 234 (18.2%), CML 177 (13.8%), MDS 97 (7.5%), NHL 35 (2.7%) and other malignancy 31 (2.4%), while 339 (26.9%) for non-malignant disorders, including SAA 202 (15.7%), immunodeficiencies 61 (4.7%), inborn errors of metabolism 40 (3.1%), Fanconi anaemia 19 (1.5%) and others 17 (1.3%). Out of 1053 recipients of auto-HSCT, 168 (16%) were transplanted for neuroblastoma, 129 (12.2%) for NHL, 124 (11.7%) for AML, 114 (10.8%) for ALL, 109 (10.4%) for Hodgkin's disease, 62 (5.9%) for Ewing's sarcoma, 16 (1.5%) for CNS tumour, 15 (1.4%) for Wilms tumour and 316 (30%) for other tumours. In 2001, the EBMT in collaboration with the European School of Haematology (ESH) developed the Outreach Programme, that is a programme supporting emerging HSCT projects and transplant centres in countries with limited resources and/or experience.

Haematopoietic stem cell transplantation trends in children over the last three decades: a survey by the paediatric diseases working party of the European Group for Blood and Marrow Transplantation.

This paper describes the trends in haematopoietic stem cell transplantation (HSCT) activity for children in Europe over the last three decades. We analysed 31,713 consecutive paediatric HSCTs reported by the European Group for Blood and Marrow Transplantation (EBMT) centres between 1970 and 2002. Data were taken from the EBMT registry and were compared according to period and centre category (paediatric or combined). Since 1996, there has been a significant increase in the number of HSCTs performed exclusively by paediatric centres, as well as in the number of alternative donor HSCTs, and in the use of peripheral blood stem cells (P<0.0001). The number of allogeneic HSCTs (allo-HSCTs) for acute lymphoblastic leukaemia, acute myeloblastic leukaemia and chronic myeloid leukaemia remained stable, whereas it increased for myelodysplastic syndromes and lymphomas, and decreased significantly for non-malignant diseases (P<0.0001). Multivariate analysis showed that younger age, human leukocyte antigen genoidentical donors, HSCT performed after 1996 and transplant centres performing more than 10 allo-HSCT/year were all associated with decreased transplant-related mortality (TRM) (P<0.0001). The number of autologus HSCTs (auto-HSCTs) for acute leukaemia decreased significantly, whereas it increased for solid tumours (P<0.0001). Multivariate analysis showed that both auto-HSCT performed before 1996 and paediatric solid tumours (P<0.0001) had higher TRM. Indications for paediatric HSCT have changed considerably during the last seven years. These changes provide tools for decision making in health-care planning and counselling.

Impact of cumulative anthracycline dose, preparative regimen and chronic graft-versus-host disease on pulmonary and cardiac function in children 5 years after allogeneic hematopoietic stem cell transplantation: a prospective evaluation on behalf of the EBMT Pediatric Diseases and Late Effects Working Parties.

This prospective study focused on risk factors and clinical outcome of pulmonary and cardiac late effects after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We prospectively evaluated 162 children by pulmonary function tests (PFTs) and cardiac shortening fraction (SF) before allo-HSCT and yearly up to the 5th year of follow-up. The 5-year cumulative incidence of lung and cardiac impairment was 35 (hazard rate=0.03) and 26% (hazard rate=0.06), respectively. Patients presenting abnormal PFTs and SF at last follow-up were 19 and 13%, respectively, with a median Lansky performance status of 90% (70-100). Chronic graft-versus-host disease (c-GVHD) was the major risk factor for reduced lung function in univariate (P=0.02) and multivariate analysis (P=0.02). Total body irradiation (TBI) alone and TBI together with pre-transplant anthracycline administration were significant risk factors for reduced cardiac function in univariate analysis, only (P=0.04 and 0.004, respectively). In conclusion, our prospective study demonstrates an asymptomatic post-allo-HSCT deterioration of pulmonary and cardiac function in some long-term survivors, who had been transplanted in childhood, and thus emphasizes the need for lifelong cardiopulmonary monitoring and the development of new strategies both to reduce pre-transplant cardiotoxic regimens and to treat more efficiently c-GVHD.

Allogeneic and autologous transplantation for haematological diseases, solid tumours and immune disorders: definitions and current practice in Europe.

The Accreditation Subcommittee of the EBMT regularly publishes special reports on current practice of haemopoietic stem cell transplantation for haematological diseases, solid tumours and immune disorders in Europe. Major changes have occurred since the first report was published in 1996. Haemopoietic stem cell transplantation today includes grafting with allogeneic and autologous stem cells derived from bone marrow, peripheral blood and cord blood. With reduced intensity conditioning regimens in allogeneic transplantation, the age limit has increased, permitting the inclusion of older patients. New indications have emerged such as autoimmune disorders and AL amyloidosis for autologous, and solid tumours for allogeneic transplants. The introduction of alternative therapies has challenged well-established indications such as imatinib for chronic myeloid leukaemia. An updated report with revised tables and operating definitions is presented here.

Receptors for plasminogen activator, urokinase, in normal and Rous sarcoma virus-transformed mouse fibroblasts.

We have prepared a conjugate of the plasminogen activator urokinase (UK) and ferritin, which maintains fibrinolytic activity. Monolayers of BALB/c-3T3 cells and of Rous sarcoma virus-transformed highly malignant line AA12-3T3, subcultured in plasminogen-free serum, were incubated with UK-ferritin at 0 degree and processed for transmission electron microscopy. Under these conditions, both of the lines showed specific receptors on the cell surface that were distributed in singlets, in small or large clusters. In the presence of excess native UK, the binding of ferritin was reduced by 99%, indicating the interaction of UK:ferritin with a specific receptor. The ligand-receptor interaction involves the catalytic site of UK, since the binding was completely impaired by preincubation of UK:ferritin with p-aminobenzamidine, a competitive inhibitor of the catalytic site of UK. The number and density of receptors decreased about one order of magnitude on the membrane of AA12 cells when compared with normal 3T3 cells. Saturation kinetics, using 125I-labeled UK, indicate the presence of 4 X 10(4) and 2.5 X 10(3) receptors on the membrane of 3T3 and AA12 cells, respectively. At 37 degrees, UK:ferritin redistributed on the plane of the membrane, in a process which was faster in malignant than in normal cells. Ferritin particles clustered in large groups on coated areas of the surface and were internalized by adsorptive pinocytosis. After 10 min at 37 degrees, the vesicles showed a progressively deeper internalization and a fusion with lysosomes, and some were observed in the Golgi complex area. Since the experiments were planned in order to exclude the presence of protease-nexin in the incubation medium, these data suggest the existence of a plasminogen-independent novel receptor for the catalytic site of plasminogen activators, the number on the cell surface of which decreases in Rous sarcoma virus-transformed mouse fibroblasts.