Plasma Levels of Intact and Cleaved Urokinase Receptor Decrease in HIV-1-Infected Patients Initiating Highly Active Antiretroviral Therapy

Prediction of Survival by IL-6 in a Randomized Placebo-Controlled Trial of Anakinra in COVID-19 Cytokine Storm

(1) Background: Some severe COVID-19 patients develop hyperinflammatory cytokine storm syndrome (CSS). We assessed the efficacy of anakinra added to standard of care (SoC) in hospitalized COVID-19 CSS patients. (2) Methods: In this single-center, randomized, double-blind, placebo-controlled trial (NCT04362111), we recruited adult hospitalized patients with SARS-CoV-2 infection, evidence of pneumonia, new/increasing oxygen requirement, ferritin ≥ 700 ng/mL, and at least three of the following indicators: D-dimer ≥ 500 ng/mL, platelet count < 130,000/mm3, WBC < 3500/mm3 or lymphocyte count < 1000/mm3, AST or ALT > 2X the upper limit of normal (ULN), LDH > 2X ULN, C-reactive protein > 100 mg/L. Patients were randomized (1:1) to SoC plus anakinra (100 mg subcutaneously every 6 h for 10 days) or placebo. All received dexamethasone. The primary outcome was survival and hospital discharge without need for intubation/mechanical ventilation. The data were analyzed according to the modified intention-to-treat approach. (3) Results: Between August 2020 and January 2021, 32 patients were recruited, of which 15 were assigned to the anakinra group, and 17 to the placebo group. Two patients receiving the placebo withdrew within 48 h and were excluded. The mean age was 63 years (SD 10.3), 20 (67%) patients were men, and 20 (67%) were White. At Day 10, one (7%) patient receiving anakinra and two (13%) patients receiving the placebo had died (p = 1.0). At hospital discharge, four (27%) patients receiving anakinra and four (27%) patients receiving the placebo had died. The IL-6 level at enrollment was predictive of death (p < 0.01); anakinra use was associated with decreases in CXCL9 levels. (4) Conclusions: Anakinra added to dexamethasone did not significantly impact the survival of COVID-19 pneumonia patients with CSS. Additional studies are needed to assess patient selection and the efficacy, timing, and duration of anakinra treatment for COVID-19 CSS.

Soluble Urokinase Plasminogen Activator Receptor (suPAR) and All-Cause and Cardiovascular Mortality in Diverse Hemodialysis Patients

Introduction

The soluble receptor of urokinase plasminogen activator (suPAR) is an innate immunity/inflammation biomarker predicting cardiovascular (CV) and non-CV events in various conditions, including type 2 diabetic patients on dialysis. However, the relationship between suPAR and clinical outcomes in the hemodialysis population at large has not been tested.

Methods

We measured plasma suPAR levels (R&D enzyme-linked immunosorbent assay [ELISA]) in 1038 hemodialysis patients with a follow-up of 2.9 years (interquartile range = 1.7−4.2) who were enrolled in the PROGREDIRE study, a cohort study involving 35 dialysis units in 2 regions in Southern Italy.

Results

suPAR was strongly (P < 0.001) and independently related to female gender (β = −0.160), age (β = 0.216), dialysis vintage (β = 0.264), CV comorbidities (β = 0.105), alkaline phosphatase (β = 0.136), albumin (β = −0.147), and body mass index (BMI; β = 0.174) (all P < 0.006). In fully adjusted analyses, suPAR tertiles predicted the risk of all-cause mortality (third tertile vs. first tertile hazard ratio (HR) = 1.91, 95% confidence interval (CI) = 1.47 – 2.48, P < 0.001), CV mortality (HR = 1.47, 95% CI = 1.03–2.09, P = 0.03), and non-CV mortality (HR = 1.94, 95% CI = 1.28–2.93, P = 0.002); these relationships were not modified by diabetes or other risk factors. suPAR added only modest prognostic risk discrimination and reclassification power for these outcomes to parsimonious models based on simple clinical variables.

Conclusion

In conclusion, suPAR robustly predicted all-cause and both CV and non-CV mortality in a large unselected hemodialysis population. Intervention studies are needed to definitively test the hypothesis that suPAR is causally implicated in clinical outcomes in this population.

Soluble Urokinase Receptors in Focal Segmental Glomerulosclerosis: A Review on the Scientific Point of View

Focal segmental glomerulosclerosis (FSGS) is one of the primary glomerular disorders in both children and adults which can progress to end-stage renal failure. Although there are genetic and secondary causes, circulating factors have also been regarded as an important factor in the pathogenesis of FSGS, because about 40% of the patients with FSGS have recurrence after renal transplantation. Soluble urokinase-type plasminogen activator receptor (suPAR) is a soluble form of uPAR, which is a membrane-bound protein linked to GPI in various immunologically active cells, including podocytes. It has recently been suggested as a potential circulating factor in FSGS by in vitro podocyte experiments, in vivo mice models, and human studies. However, there have also been controversies on this issue, because subsequent studies showed conflicting results. suPAR levels were also increased in patients with other glomerular diseases and were inversely correlated with estimated glomerular filtration rate. Nevertheless, there has been no balanced review on this issue. In this review, we compare the conflicting data on the involvement of suPAR in the pathogenesis of FSGS and shed light on interpretation by taking into account many points and the potential variables and confounders influencing serum suPAR levels.

Full-length soluble urokinase plasminogen activator receptor down-modulates nephrin expression in podocytes

Increased plasma level of soluble urokinase-type plasminogen activator receptor (suPAR) was associated recently with focal segmental glomerulosclerosis (FSGS). In addition, different clinical studies observed increased concentration of suPAR in various glomerular diseases and in other human pathologies with nephrotic syndromes such as HIV and Hantavirus infection, diabetes and cardiovascular disorders. Here, we show that suPAR induces nephrin down-modulation in human podocytes. This phenomenon is mediated only by full-length suPAR, is time-and dose-dependent and is associated with the suppression of Wilms’ tumor 1 (WT-1) transcription factor expression. Moreover, an antagonist of αvβ3 integrin RGDfv blocked suPAR-induced suppression of nephrin. These in vitro data were confirmed in an in vivo uPAR knock out Plaur^−/− mice model by demonstrating that the infusion of suPAR inhibits expression of nephrin and WT-1 in podocytes and induces proteinuria. This study unveiled that interaction of full-length suPAR with αvβ3 integrin expressed on podocytes results in down-modulation of nephrin that may affect kidney functionality in different human pathologies characterized by increased concentration of suPAR.

Soluble urokinase plasminogen activator receptor (suPAR) is a novel, independent predictive marker of myocardial infarction in HIV-1-infected patients: a nested case-control study

Objectives

Patients infected with HIV are at increased risk of myocardial infarction (MI). Increased plasma levels of the inflammatory biomarker soluble urokinase plasminogen activator receptor (suPAR) have been associated with increased risk of cardiovascular diseases (CVD), including MI in the general population. We tested suPAR as a predictive biomarker of MI in HIV‐1‐infected individuals.

Methods

suPAR levels were investigated in a nested case‐control study of 55 HIV‐1‐infected cases with verified first‐time MI and 182 HIV‐1‐infected controls with no known CVD. Controls were matched for age, gender, duration of antiretroviral therapy (ART), smoking and no known CVD. suPAR was measured in the four plasma samples available for each patient at different time‐points; 1, Before initiation of ART; 2, 3 months after initiation of ART; 3, 1 year before the case's MI; and 4, The last sample available before the case's MI.

Results

In unadjusted conditional regression analysis, higher levels of suPAR were associated with a significant increase in risk of MI at all time‐points. Patients in the third and fourth suPAR quartiles had a three‐ to 10‐fold higher risk of MI compared to patients in the lowest suPAR quartile at all time‐points. suPAR remained a strong significant predictor of MI, when adjusting for HIV‐1 RNA, total cholesterol, triglycerides and high‐density lipoprotein.

Conclusion

Elevated suPAR levels were associated with increased risk of MI in HIV‐infected patients, suggesting that suPAR could be a useful biomarker for prediction of first‐time MI in this patient group, even years before the event.

Urokinase-type plasminogen activator receptor as a predictor of poor outcome in patients with systemic inflammatory response syndrome

BACKGROUND

Urokinase-type plasminogen activator (uPA) and urokinase-type plasminogen activator receptor (uPAR) are known as important factors, which mediate a variety of functions in terms of vascular homeostasis, inflammation and tissue repair. However, their role in systemic inflammatory response syndrome (SIRS) has been less well studied. This study aimed to test the hypothesis that the abnormalities of fibrinolysis and degradation of extracellular matrix mediated by uPA and uPAR are directly related to the patients with SIRS. We therefore analyzed their role and clinicopathological significance in patients with SIRS.

METHODS

A case-control study was conducted with 85 patients who were divided into two groups according to the diagnostic criteria of SIRS: SIRS group (n=50) and non-SIRS group (n=35). The SIRS group was divided into MODS group (n=26) and non-MODS group (n=24) by their severity, and survival group (n=35) and non-survival group (n=15) by their prognosis. Another 30 healthy adults served as normal controls. uPA and uPAR in plasma were detected by commercial enzyme-linked immunosorbent assay (ELISA) kits.

RESULTS

The plasma level of uPA was lower in the SIRS group than in the non-SIRS group and controls (P<0.001 and P<0.001). It was lower in sepsis patients and the MODS group than in the non-sepsis patients and the non-MODS patients (all P<0.05). However, there was no difference in uPA level between survivors and non-survivors (P>0.05). The plasma level of uPAR increased in the SIRS group compared with the non-SIRS group and controls (P<0.001 and P<0.001). There was a significant elevation of uPAR in sepsis patients, MODS patients and non-survivors as compared with non-sepsis patients, non-MODS patients and survivors respectively (all P<0.05). Plasma uPAR levels were positively correlated with APACHE II score (r=0.575, P<0.001) and SOFA score (r=0.349, P=0.013). AUCs for the prediction of SIRS mortality were 0.67 and 0.51, respectively, for uPA and uPAR.

CONCLUSION

uPAR could be a predictor of poor outcome in patients with SIRS.

Hospital mortality prognostication in sepsis using the new biomarkers suPAR and proADM in a single determination on ICU admission

PURPOSE

The soluble form of the urokinase-type plasminogen activator receptor (suPAR) and proadrenomedullin (proADM) are two new and promising sepsis biomarkers. We assessed the prognostic value of a single determination of proADM and suPAR, comparing them with C-reactive protein (CRP) and procalcitonin (PCT), and evaluating whether their addition to severity scores (APACHE II and SOFA) could improve their prognostic accuracy.

METHODS

A single-centre prospective observational study conducted in an adult intensive care department at Marques de Valdecilla University Hospital in Spain. APACHE II and SOFA scores, CRP, PCT, suPAR and proADM levels on the day of ICU admission were collected.

RESULTS

A total of 137 consecutive septic patients were studied. The best area under the curve (AUC) for the prediction of in-hospital mortality was for APACHE II (0.82) and SOFA (0.75) scores. The ROC curve for suPAR yielded an AUC of 0.67, higher than proADM (0.62), CRP (0.50) and PCT (0.44). Significant dose-response trends were found between hospital mortality and suPAR (OR Q4 = 4.83, 95% CI 1.60-14.62) and pro-ADM (OR Q4 = 3.00, 95% CI 1.06-8.46) quartiles. Non-significant associations were found for PCT and CRP. The combination of severity scores and each biomarker did not provide superior AUCs.

CONCLUSIONS

SuPAR and, to a lesser extent, proADM levels on ICU admission were better tools in prognosticating in-hospital mortality than CRP or PCT. However, neither of the two new biomarkers has been demonstrated to be excessively useful in the current setting. The prognostic accuracy was better for severity scores than for any of the biomarkers.

HIV-1 infected lymphoid organs upregulate expression and release of the cleaved form of uPAR that modulates chemotaxis and virus expression

Cell-associated receptor for urokinase plasminogen activator (uPAR) is released as both full-length soluble uPAR (suPAR) and cleaved (c-suPAR) form that maintain ability to bind to integrins and other receptors, thus triggering and modulating cell signaling responses. Concerning HIV-1 infection, plasma levels of suPAR have been correlated with the severity of disease, levels of immune activation and ineffective immune recovery also in individuals receiving combination anti-retroviral therapy (cART). However, it is unknown whether and which suPAR forms might contribute to HIV-1 induced pathogenesis and to the related state of immune activation. In this regard, lymphoid organs represent an import site of chronic immune activation and virus persistence even in individuals receiving cART. Lymphoid organs of HIV-1(+) individuals showed an enhanced number of follicular dendritic cells, macrophages and endothelial cells expressing the cell-associated uPAR in comparison to those of uninfected individuals. In order to investigate the potential role of suPAR forms in HIV-1 infection of secondary lymphoid organs, tonsil histocultures were established from HIV-1 seronegative individuals and infected ex vivo with CCR5- and CXCR4-dependent HIV-1 strains. The levels of suPAR and c-suPAR were significantly increased in HIV-infected tonsil histocultures supernatants in comparison to autologous uninfected histocultures. Supernatants from infected and uninfected cultures before and after immunodepletion of suPAR forms were incubated with the chronically infected promonocytic U1 cell line characterized by a state of proviral latency in unstimulated conditions. In the contest of HIV-conditioned supernatants we established that c-suPAR, but not suPAR, inhibited chemotaxis and induced virus expression in U1 cells. In conclusion, lymphoid organs are an important site of production and release of both suPAR and c-suPAR, this latter form being endowed with the capacity of inhibiting chemotaxis and inducing HIV-1 expression.

Assessment of simple risk markers for early mortality among HIV-infected patients in Guinea-Bissau: a cohort study

BACKGROUND

Decisions about when to start an antiretroviral therapy (ART) are normally based on CD4 cell counts and viral load (VL). However, these measurements require equipment beyond the capacity of most laboratories in low-income and middle-income settings. Thus, there is an urgent need to identify and test simple markers to guide the optimal time for starting and for monitoring the effect of ART in developing countries.

OBJECTIVES

(1) To evaluate anthropometric measurements and measurement of plasma-soluble form of the urokinase plasminogen activator receptor (suPAR) levels as potential risk factors for early mortality among HIV-infected patients; (2) to assess whether these markers could help identify patients to whom ART should be prioritised and (3) to determine if these markers may add information to CD4 cell count when VL is not available.

DESIGN

An observational study.

SETTING

The largest ART centre in Bissau, Guinea-Bissau.

PARTICIPANTS

1083 ART-naïve HIV-infected patients.

OUTCOME MEASURES

Associations between baseline anthropometric measurements, CD4 cell counts, plasma suPAR levels and survival were examined using Cox proportional hazards models.

RESULTS

Low body mass index (BMI≤18.5 kg/m(2)), low mid-upper-arm-circumference (MUAC≤250 mm), low CD4 cell count (≤350 cells/μl) and high suPAR plasma levels (>5.3 ng/ml) were independent predictors of death. Furthermore, mortality among patients with low CD4 cell count, low MUAC or low BMI was concentrated in the highest suPAR quartile.

CONCLUSIONS

Irrespective of ART initiation and baseline CD4 count, MUAC and suPAR plasma levels were independent predictors of early mortality in this urban cohort. These markers could be useful in identifying patients at the highest risk of short-term mortality and may aid triage for ART when CD4 cell count is not available or when there is shortness of antiretroviral drugs.

Urokinase plasminogen activator inhibits HIV virion release from macrophage-differentiated chronically infected cells via activation of RhoA and PKCε

BACKGROUND

HIV replication in mononuclear phagocytes is a multi-step process regulated by viral and cellular proteins with the peculiar feature of virion budding and accumulation in intra-cytoplasmic vesicles. Interaction of urokinase-type plasminogen activator (uPA) with its cell surface receptor (uPAR) has been shown to favor virion accumulation in such sub-cellular compartment in primary monocyte-derived macrophages and chronically infected promonocytic U1 cells differentiated into macrophage-like cells by stimulation with phorbol myristate acetate (PMA). By adopting this latter model system, we have here investigated which intracellular signaling pathways were triggered by uPA/uPAR interaction leading the redirection of virion accumulation in intra-cytoplasmic vesicles.

RESULTS

uPA induced activation of RhoA, PKCδ and PKCε in PMA-differentiated U1 cells. In the same conditions, RhoA, PKCδ and PKCε modulated uPA-induced cell adhesion and polarization, whereas only RhoA and PKCε were also responsible for the redirection of virions in intracellular vesicles. Distribution of G and F actin revealed that uPA reorganized the cytoskeleton in both adherent and polarized cells. The role of G and F actin isoforms was unveiled by the use of cytochalasin D, a cell-permeable fungal toxin that prevents F actin polymerization. Receptor-independent cytoskeleton remodeling by Cytochalasin D resulted in cell adhesion, polarization and intracellular accumulation of HIV virions similar to the effects gained with uPA.

CONCLUSIONS

These findings illustrate the potential contribution of the uPA/uPAR system in the generation and/or maintenance of intra-cytoplasmic vesicles that actively accumulate virions, thus sustaining the presence of HIV reservoirs of macrophage origin. In addition, our observations also provide evidences that pathways controlling cytoskeleton remodeling and activation of PKCε bear relevance for the design of new antiviral strategies aimed at interfering with the partitioning of virion budding between intra-cytoplasmic vesicles and plasma membrane in infected human macrophages.

Correlation between soluble urokinase plasminogen activator receptor with CD4 T lymphocyte and WHO clinical staging of HIV infection

The urokinase-type plasminogen activator (uPA) and its receptor play a key role in pericellular proteolysis, cell migration and signal transduction. Previous study showed that suPAR could be used as an independent prognostic marker of disease progression in HIV-1 patients.1,17 Immune status of HIV patient and progressivity of disease are important parameters used as clinical concideration before initiating anti retroviral treatment and for monitoring treatment effectivity. Recently immune status of HIV patients is determined by CD4 T lymphocyte counting which represents the remaining healthy lymphocyte T expressing CD4 that very expensive and need special laboratory equipment. Destruction and shedding of T lymphocyte, macrophage and natural killer cell will deliver soluble urokinase plasminogen activator receptor, a surface protein which is expressed by those cells and can be measured by ELISA8,9,11. This study objective is to determine correlation between suPAR plasma concentration and CD4 T lymphocyte and WHO clinical stagging of HIV infection. Study subjects. Fifty four naieve HIV-1-infected patients (32 males, and 22 females) are participant in a cross sectional study enrolled on 22 November 2007 until 31 july 2008 at the department of infectious disease Saiful Anwar Hospital, Malang, Indonesia. Blood sampling. Two blood samples were drawn before treatment, CD4 counts were measured with an Epics XL-MCL Coulter flowcytometer. EDTA plasma for suPAR measurement was stored at -80°C. Data are presented as mean±standart deviation. P<0.05 is considered significant. Statistical calculations were done using SSPS 15. Patients (n = 54) enrolled and clustered according to WHO clinical stage ( I - IV) at inclusion. All HIV-infected patients had measurable levels of plasma suPAR with a median value of 8,9 ng/mL(range 1,65-29,7 ng/mL). Pearson correlation demonstrated a weak but significant negative between suPAR and CD4 T lymphocyte count (p=-0.634, p<.0005). suPAR level positively correlated with the WHO-defined clinical stages (P< .0005, spearman correlation test, r=0,87). There were significant difference between each stage i.e I(1,6± o,61ng/mL), II(3.04±1.03 ng/mL), III (10.53±7.1ng/mL) and IV (20.42±10.81ng/mL) (P< .0005, Spearman test). In addition pearson correlation demonstrated a weak but significant negative correlation between suPAR and CD4 count (p=-0.66; P<.0005). There were negative significant correlatio between CD4 count and suPAR level, suggested that suPAR could provide as a complementary biological marker for HIV-1 although it can not replace the CD4 count. SuPAR plasma concentration and clinical stage give significantly correlation with WHO clinical staging of HIV infection.

Enhanced levels of urokinase plasminogen activator and its soluble receptor in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by defective immunoglobulin production and high frequency of bacterial infections, autoimmunity and manifestations of chronic inflammation. The urokinase plasminogen activator (uPA), its cell bound and soluble receptor (uPAR, suPAR) have complex biological functions involving innate immune defense mechanisms and regulation of inflammation. Based on this dual role, we hypothesized that the uPA system could be affected in CVID, and examined expression of components of the uPA system in subgroups of CVID. All CVID-patients had increased plasma levels of suPAR with particularly high levels in those with splenomegaly and thrombocytopenia. Plasma uPA levels were also raised in these patients, and both suPAR and uPA levels correlated with the monocyte activation marker neopterin. Monocytes from CVID patients had increased expression of uPAR. We show an increased activation of the uPA system possibly contributing to the inflammatory phenotype seen in subgroups of CVID patients.

Ligand-engaged urokinase-type plasminogen activator receptor and activation of the CD11b/CD18 integrin inhibit late events of HIV expression in monocytic cells

Urokinase-type plasminogen activator (uPA) signaling via its receptor uPAR inhibits late events in HIV-1 replication in acutely infected primary monocyte-derived macrophages (MDMs) and promonocytic U937 cells. Here we show that U937-derived, chronically infected U1 cells stimulated with phorbol 12-myristate 13-acetate (PMA) express integrins, uPA, and soluble uPAR at levels similar to those of MDMs. uPA inhibited HIV expression in U1 cells incubated with either PMA or tumor necrosis factor-alpha (TNF-alpha), but not with other HIV-inductive cytokines or lipopolysaccharide. Of interest, only PMA and TNF-alpha, but not other HIV-inductive stimuli, induced surface expression of the alpha(M) chain CD11b in U1 cells constitutively expressing CD18, the beta(2) chain of the Mac-1 integrin. Like uPA, fibrinogen, a Mac-1 (CD11b/CD18) ligand, and M25, a peptide homologous to a portion of the beta-propeller region of CD11b preventing its association with uPAR, inhibited HIV virion release in PMA-stimulated U1 cells. Both uPAR small-interference RNA (siRNA) and soluble anti-beta(1)/-beta(2) monoclonal antibodies abolished the anti-HIV effects of uPA, whereas CD11b siRNA reversed the anti-HIV effect of M25, but not that induced by uPA. Thus, either uPA/uPAR interaction, Mac-1 activation, or prevention of its association with uPAR triggers a signaling pathway leading to the inefficient release of HIV from monocytic cells.

Reduced mortality and CD4 cell loss among carriers of the interleukin-10 -1082G allele in a Zimbabwean cohort of HIV-1-infected adults

OBJECTIVES

To evaluate the effect on HIV progression of single nucleotide polymorphisms in promoters of the genes for tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 and known to influence cytokine production.

METHODS

Survival was documented for 4.3 years after baseline for 198 HIV-1-infected and 180 HIV-uninfected individuals from the Mupfure Schistosomiasis and HIV Cohort in rural Zimbabwe. Polymorphisms determined were -592C>A and -1082A>G for IL-10 and -238G>A and -308G>A for TNF-alpha. CD4 cell counts, plasma HIV RNA, soluble TNF receptor II (sTNF-rII), IL-8 and IL-10 were also measured.

RESULTS

Mortality was lower in carriers of the IL-10 -1082G high-producer allele (hazard ratio, 0.47; P < 0.01). CD4 cell count decrease in participants reporting for the follow-up at 3 years was attenuated in carriers of this allele (P < 0.01). In univariate analysis, plasma IL-10, IL-8, and sTNF-rII correlated negatively with CD4 cell count, positively with HIV RNA, and higher levels predicted mortality. In multivariate analysis only sTNF-rII was an independent predictor of HIV progression markers and mortality. Indeed, sTNF-rII predicted mortality (P < 0.01) at a level of significance comparable to HIV RNA (P < 0.01) and CD4 cell count (P < 0.05).

CONCLUSIONS

In carriers of IL-10 -1082G, an allele linked to increased IL-10 production, survival was doubled and CD4 cell decrease was attenuated compared with noncarriers. Only sTNF-rII and not plasma IL-10 was an independent predictor of HIV progression markers and mortality. This study supports immune activation as a driving force in HIV pathogenesis and indicates a protective role of IL-10 -1082G that should be evaluated in other cohorts.

Inhibition of HIV replication by the plasminogen activator is dependent on vitronectin-mediated cell adhesion

Urokinase-type plasminogen activator (uPA), an inducer of macrophage adhesion, inhibits HIV-1 expression in PMA-stimulated, chronically infected U1 cells. We investigated whether uPA-dependent cell adhesion played a role in uPA-dependent inhibition of HIV-1 replication in these cells. Monocyte-derived macrophages (MDM) were generated from monocytes of HIV-infected individuals or from cells of seronegative donors infected acutely in vitro. U1 cells were stimulated in the presence or absence of uPA in standard tissue culture (TC) plates, allowing firm cell adhesion or ultra-low adhesion (ULA) plates. Moreover, U1 cells were also maintained in the presence or absence of vitronectin (VN)-containing sera or serum from VN(-/-) mice. Virus production was evaluated by RT activity in culture supernatants, whereas cell adhesion was by crystal violet staining and optical microscopy. uPA inhibited HIV replication in MDM and PMA-stimulated U1 cells in TC plates but not in ULA plates. uPA failed to inhibit HIV expression in U1 cells stimulated with IL-6, which induces virus expression but not cell adhesion in TC plates. VN, known to bind to the uPA/uPA receptor complex, was crucial for these adhesion-dependent, inhibitory effects of uPA on HIV expression, in that they were not observed in TC plates in the presence of VN(-/-) mouse serum. HIV production in control cell cultures was increased significantly in ULA versus TC plates, indicating that macrophage cell adhesion per se curtails HIV replication. In conclusion, uPA inhibits HIV-1 replication in macrophages via up-regulation of cell adhesion to the substrate mediated by VN.