Fibronectin and complement secretion by monocytes and peritoneal macrophages in vitro from patients undergoing continuous ambulatory peritoneal dialysis

Peritoneal Defence Mechanisms and Staphylococcus Aureus in Patients Treated with Continuous Ambulatory Peritoneal Dialysis (CAPD)

Peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients due to S. aureus is associated with an adverse clinical outcome, suggesting impaired clearance of this organism by the host. The ability of peritoneal macrophages (PMO) derived from CAPD patients to take up S. aureus and mount a respiratory burst was investigated. Whilst significant activity was observed in the absence of opsonin, both parameters of phagocytosis were augmented by addition of 20% pooled human serum (PHS), complement-depleted PHS, and fibronectin. When used as sole opsonin, fibronectin resulted in a dose-related increase in chemiluminescent response by both blood neutrophils and PMO.

The opsonic activity of dialysis effluent, as judged by neutrophil chemiluminescence, correlated with IgG and fibronectin content, but not with complement as assessed by C3 levels. The addition of urokinase to dialysate improved its opsonic properties whilst having no effect on the activity of PHS-20%; this would suggest that the formation of fibrin in dialysate, promoted by S. aureus, interferes with phagocytosis. This and the low IgG, complement and fibronectin levels in dialysate may explain in part the relatively poor clearance of this organism from the peritoneum.

Fibronectin in the Normal Peritoneal Fluids of Patients on Chronic Ambulatory Peritoneal Dialysis (CAPD) and during Peritonitis

The authors have studied the fibronectin (Fn) levels in peritoneal fluids from patients on CAPD. The assay system used is based on ELISA using a monoclonal antibody to Fn. We have tried to determine whether in some of these patients repeated intraperitoneal infections bear any relationship with peritoneal Fn levels. We find that the Fn levels in the peritoneal fluids from these patients are about one twentieth those found in normal plasma. Also we have found that the peritoneal Fn levels significantly increase during peritonitis and come back to normal levels within a few days of the clearing of the peritoneal fluid. We have found no connection between normal peritoneal fluid Fn concentration and subsequent peritonitis. However, the numbers are too small to permit statistical evaluation. The Fn levels were not affected by the presence or absence of heparin in the Dineal fluids. Large day to day variations were seen in the Fn levels in the peritoneal fluid of individual patients. It is not clear from this study, whether the low levels of Fn in the peritoneal fluid reflect a deficit in the local Fn production or are due to dilutional effects.

Fibronectin and Fibrinogen in the Plasma and Dialysate of Patients on CAPD

Plasma and dialysate fluid from 18 patients treated with continuous ambulatory peritoneal dialysis (CAPD) while peritonitis -free, were analysed for fibronectin (FN), fibrinogen (FG), albumin (ALB) and total protein (TP). Mean plasma FG (6.24 g/l) was higher than for normal controls (4.23 g/1; p < 0.001) whereas FN (0.31 g/l) was lower than for normal (0.36 g/l; p < 0.02). Twenty-four hour losses of proteins into the dialysate were as follows: TP = 10.9 g, ALB = 5.2 g, FN = 15.6 mg and FG = 221 mg. Mean dialysate concentration for FN was 2.09 mg/1 and FG 31.1 mg/l. Dialysate FN and FG correlated with dialysate ALB (r = 0.92; p < 0.001, r = 0.60; p < 0.01 respectively) suggesting an ultrafiltrate rather than synthesis within the peritoneum.

Protein Adsorption onEX VIVOCatheters and Polymers Exposed to Peritoneal Dialysis Effluent

Background

Deposition of proteins on surfaces of medical devices has been recognized to putatively relate to the process of regulation of biomaterial-associated complications by attachment of fibrin clots, eukaryotic cells, and microbes. The molecules adsorb to a varying extent, depending not only on the physicochemical properties of the biomaterial, but also on the composition of the host fluid.

Objective

Adsorption of proteins on catheters exposed both ex vivo and in vitro to dialysate of patients on peritoneal dialysis (PD) was studied.

Methods

Peritoneal dialysis effluent was collected from 5 patients with end-stage renal disease on continuous ambulatory PD. Tenckhoff catheters were obtained from 16 patients. Deposition of proteins on excised Tenckhoff catheters and tubing of different materials exposed to PD effluent in vitro was studied using125iodine-labeled antibodies. Adhesion of Staphylococcus aureus and Staphylococcus epidermidis strains was quantified on tubing exposed to PD effluent in vitro.

Results

The presence of albumin, transferrin, immunoglobulin G, fibrinogen, fibronectin, von Willebrand factor, vitronectin, and thrombospondin was determined at various concentrations in PD effluent. All proteins analyzed were detected on PD catheters removed from patients. The extent of protein deposition on Tenckhoff catheters exposed to PD effluent, in vitro, rapidly reached a plateau and remained constant, as it did on polyvinyl chloride and polyethylene tubing. Adhesion of staphylococci was enhanced on Tenckhoff catheters exposed to PD effluent compared to unused PD solution.

Conclusions

The data identify surface exposed proteins that may serve as adhesion sites for microbes on peritoneal catheters indwelled in patients undergoing PD.

Antibacterial responses by peritoneal macrophages are enhanced following vitamin D supplementation

Patients with chronic kidney disease (CKD), who usually display low serum 25-hydroxyvitamin D (25D) and 1,25-dihydroxyvitamin D (1,25D), are at high risk of infection, notably those undergoing peritoneal dialysis (PD). We hypothesized that peritoneal macrophages from PD patients are an important target for vitamin D-induced antibacterial activity. Dialysate effluent fluid was obtained from 27 non-infected PD patients. Flow cytometry indicated that PD cells were mainly monocytic (37.9±17.7% cells CD14+/CD45+). Ex vivo analyses showed that PD cells treated with 25D (100 nM, 6 hrs) or 1,25D (5 nM, 6 hrs) induced mRNA for antibacterial cathelicidin (CAMP) but conversely suppressed mRNA for hepcidin (HAMP). PD cells from patients with peritonitis (n = 3) showed higher baseline expression of CAMP (18-fold±9, p<0.05) and HAMP (64-fold±7) relative to cells from non-infected patients. In 12 non-infected PD patients, oral supplementation with a single dose of vitamin D2 (100,000 IU) increased serum levels of 25D from 18±8 to 41±15 ng/ml (p = 0.002). This had no significant effect on PD cell CD14/CD45 expression, but mRNA for HAMP was suppressed significantly (0.5-fold, p = 0.04). Adjustment for PD cell CD14/CD45 expression using a mixed linear statistical model also revealed increased expression of CAMP (mRNA in PD cells and protein in effluent) in vitamin D-supplemented patients. These data show for the first time that vitamin D supplementation in vitro and in vivo promotes innate immune responses that may enhance macrophage antibacterial responses in patients undergoing PD. This highlights a potentially important function for vitamin D in preventing infection-related complications in CKD.

Anti-inflammatory drugs modulate C1q secretion in human peritoneal macrophages in vitro

The complement system plays an important role in the humoral immune response. Activation of the classical complement pathway is mediated by its subcomponent, C1q, which is involved in the pathogenesis of several autoimmune disorders. Among the main C1q-synthesising tissues, macrophages have been attributed as the main source. We investigated the effects of anti-inflammatory drugs (methylprednisolone and acetylsalicylic acid (ASA)) on C1q secretion in human peritoneal macrophages in vitro. The macrophages were isolated from peritoneal lavage fluid of patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis, and were maintained in culture for up to 6 days. ASA decreased while methylprednisolone increased C1q secretion from human peritoneal macrophages in vitro, which correlated well with the percentage of CD14 positive cells after treatment. We conclude that different response of the macrophages to treatment with methylprednisolone and ASA may point out to the importance of macrophage activation after treatment, as well as an increased abundance of membrane C1q accompanied by increased phagocytosis.

Prolonged exposure to glucose degradation products impairs viability and function of human peritoneal mesothelial cells

Bioincompatibility of peritoneal dialysis fluids (PDF) has been linked to the presence of glucose degradation products (GDP). Previous experiments have shown that short-term exposure to several GDP at concentrations found in commercially available PDF had no significant effect on human peritoneal mesothelial cells (HPMC). During continuous ambulatory peritoneal dialysis, however, cells are continually exposed to GDP for extended periods of time. Thus, the impact of GDP on HPMC during long-term exposure was assessed. HPMC were cultured for up to 36 d in the presence of 6 identified GDP (acetaldehyde, formaldehyde, furaldehyde, glyoxal, methylglyoxal, and 5-HMF) at doses that reflect their concentrations in conventional PDF. At regular time intervals, the ability of HPMC to secrete cytokines (interleukin-6 [IL-6]) and extracellular matrix molecules (fibronectin) was evaluated. In addition, cell viability, morphology, and proliferative potential were assessed. Exposure to GDP resulted in a significant reduction in mesothelial IL-6 and fibronectin release. Approximately 80% of this decrease occurred during the first 12 d of the exposure and was paralleled by a gradual loss of cell viability and development of morphologic alterations. After 36 d of exposure, the number of cells in GDP-treated cultures was reduced by nearly 60%. However, GDP-treated cells were able to resume normal proliferation when transferred to a normal GDP-free medium. HPMC viability and function may be impaired during long-term exposure to clinically relevant concentrations of GDP, which suggests a potential role of GDP in the pathogenesis of peritoneal membrane dysfunction during chronic peritoneal dialysis.

Infections in patients undergoing peritoneal dialysis

Considering experience acquired in the past years, it seems as though physicians have reached a plateau in the frequency of peritonitis. A peritonitis rate of 1 every 2 patient years may be acceptable. Further reduction of this peritonitis rate will require inordinately large efforts on all fronts. One will have to consider what are the acceptable costs and risks of peritonitis in patients on peritoneal dialysis. New developments in catheter technology, improved connections, better understanding of patient selection and training programs, improved diagnostic and therapeutic methods in the management of peritonitis, and understanding of the infectious and immune processes are eagerly awaited developments.

Expression of adhesion molecules and fibronectin of activated peritoneal surface with lipopolysaccharide (LPS) analyzed with immuno SEM

To disclose cell-to-cell interaction associated with the defensive mechanism of the peritoneum, the peritoneum was stimulated with lipopolysaccharide (LPS) and analyzed three-dimensionally, ultrastructurally, and immunohistochemically with immunoSEM (scanning electron microscopy). The activated hepatic peritoneal surface demonstrated numerous microvilli with the adhesion molecules ICAM-1 and VCAM-1. They were restricted to villi and peaked at 1.5 microg/g body weight of LPS. Delicate strands appeared moderately and were interwoven among microvilli with increasing LPS. These strands did not express ICAM-1 or VCAM-1, but fibronectin. Leukocytes began to adhere to the peritoneal surface above die value of LPS (2.5 microg). These results suggest that the peritoneal surface gives a defensive sheet for cell-to-cell interaction through adhesion molecules and fibronectin.

Disturbed host defense in peritoneal cavity during CAPD: characterization of responsible factors in dwell fluid

In this study, the factors in overnight dwell fluid (8 to 10 hr dwell) depressing granulocyte (GC) NAD(P)H-oxidase dependent radical species production are characterized. At present, most studies have essentially focused on fresh, unspent dialysate and on peritoneal macrophages. The response to Staphylococcus aureus (Staph A) was dose-dependently depressed for both GC CO2 production (from 91.3 +/- 8.4 to 9.0 +/- 1.5 dpm/10(3) GC, P < 0.01) and chemiluminescence (CL) (peak from 7.3 +/- 0.8 to 1.6 +/- 0.8 cps x 10(3)/GC, P < 0.01). Stimulation with formyl-methionine-leucine-phenylalanine (f-MLP), phorbol myristic acid (PMA), Staphylococcus epidermidis (Staph Epi), E. coli, latex and zymosan revealed a parallel depression, pointing to an intrinsic metabolic defect, rather than failure of particle ingestion. The addition of glucose to the normal cell medium to obtain the same concentration as in the CAPD effluent (2.9 +/- 0.3 mg/dl) depressed function but not to the same extent as the genuine PD effluent. Opsonization of Staph A and E. coli induced a partial correction. No effect of pH or osmolality was observed. HPLC fractionation of CAPD effluent on a polarity based gradient revealed an elution of depressive factors in hydrophobic fractions with a nadir in F7 and F12. Analysis of the elution pattern of various uremic solutes revealed elution in F12 of p-cresol, a solute with known inhibitory effect on GC function. These events may be related to recent peritonitis (CL in response to Staph A 0.3 +/- 0.1 in effluent of 6 patients with recent peritonitis versus 2.6 +/- 0.8 cps x 10(3)/GC in 12 patients without recent peritonitis (P < 0.01). We conclude that the GC response is depressed in the presence of CAPD effluent due to excess glucose, lack of opsonization, and uremic solutes of which p-cresol is one of the responsible compounds.

Zinc modulates mononuclear cellular calcitriol metabolism in peritoneal dialysis patients

Zinc has long been known to play a role in maintaining immunologic function. Hypozincemia, however, is common in patients with end-stage renal disease (ESRD) treated with continuous ambulatory peritoneal dialysis (CAPD). We previously demonstrated that zinc depletion limits the ability of animals to achieve maximum circulating calcitriol levels in response to the stress of calcium or phosphorus depletion. It was unclear, however, whether changes in the circulating levels of calcitriol in these settings was associated with a direct effect on renal 1-alpha hydroxylase activity, or whether the zinc dependence of the stimulated calcitriol response involved an integrated systemic response in intact animals. In addition it was unclear whether circulating zinc levels or zinc nutritional status modified calcitriol metabolism in humans. To better understand the role zinc plays in the immune response in patients with ESRD, we studied IL-1, calcitriol and tumor necrosis factor-alpha production by mononuclear cells from blood and peritoneal effluents of 22 patients with ESRD treated with CAPD. Macrophages from peritoneal effluents and peripheral blood mononuclear cells were isolated and pulsed with phytohemagglutinin in medium to which different concentrations of zinc chloride, copper chloride, and carbonyl cyanide p-(trifluoromethoxy)-phenyl-hydrazone (FCCP), an inhibitor of mitochondrial function were added. Supernatant interleukin-1, calcitriol, and tumor necrosis factor-alpha levels were subsequently measured. We demonstrated a zinc concentration dependent increase in stimulated IL-1 alpha and -beta, and TNF-alpha release in both peripheral mononuclear cells and peritoneal macrophages from patients with ESRD treated with CAPD. The effect is zinc specific, as it is not reproduced by copper or chloride supplementation. A zinc concentration dependent increase in peritoneal macrophage calcitriol release was also noted. FCCP blocked the cellular production of IL-1 alpha, IL-1 beta, and TNF-alpha, but had little effect on zinc-induced stimulated mononuclear cell supernatant calcitriol levels. The different shape of the zinc dose response curve, and the lack of correlation between paired IL-1 and calcitriol supernatant levels suggests the effect of zinc on mononuclear cellular cytokine and calcitriol production is mediated through different pathways.

Host defences in continuous ambulatory peritoneal dialysis and the genesis of peritonitis

Continuous ambulatory peritoneal dialysis (CAPD) has come to be extensively used for the treatment of end-stage renal failure in children, and especially infants, such that now more than half of children on dialysis worldwide receive treatment by this means. Peritonitis, however, is commoner in children than in adults receiving treatment, and is a major source of morbidity and treatment failure in children started on CAPD. Only recently has the immunology of the normal peritoneum been studied extensively, with the need to assess the impact of the installation of large volumes of fluid into the peritoneal sac during dialysis. The main phagocytic defences of the peritoneum depend upon a unique set of macrophages which are present free in the peritoneal fluid but also in the submesothelium and in perivascular collections together with B lymphocytes in the submesothelial area. Both the number of macrophages per unit volume and the concentration of opsonic proteins, such as IgG, complement and fibronectin, are reduced to between only 1% and 5% when dialysis fluid is continuously present in the peritoneal sac. In addition, the fluids used for CAPD are toxic to both macrophages and to mesothelial cells. Thus minor degrees of contamination frequently lead to peritonitis and in addition the majority of patients have catheters inserted in their peritoneum which become colonised with organisms capable of producing exopolysaccharide (slime), which promotes adhesion of the organism to the plastic and protects them against phagocytic attack and the penetration of antibiotics. Thus the peritoneum is in a state of continual inflammation, as well as being a markedly more vulnerable site than the normal peritoneum to the entry of organisms. Whether clinical peritonitis appears in this state of chronic contamination probably depends on perturbation in the balance between host defences and the organism. Whilst Staphylococcus epidermidis is the commonest cause of peritonitis, Staphylococcus aureus and Gram-negative organisms are much more serious and more frequently lead either to temporary catheter removal or discontinuation of dialysis altogether. This review describes the peritoneal defences in relation to the genesis of peritonitis.

Immuno-effector characteristics of peritoneal cells during CAPD treatment: a longitudinal study

Peritoneal cells (PC) from 75 patients were immuno-phenotypically and functionally characterized during the first year of CAPD treatment (PCcapd) and compared to PC obtained by laparoscopy of healthy women (control peritoneal cells). Patients were divided, according to their peritonitis incidence (PI), into a high PI (HPI) and a low PI group (LPI). The yield of PCcapd decreased significantly over the year. The differential cell count and immunophenotype of PCcapd remained unchanged in the LPI group, but the percentage of macrophages decreased over the year in the HPI group. Macrophages in the PCcapd, when compared to control peritoneal cells, had a less mature phenotype as measured by RFD7 expression but a higher Fc-receptor expression. The PCcapd showed a higher percentage of B cells, CD4 positive T cells and activated T cells bearing HLA-DR/DQ when compared to the control peritoneal cells. Over the year a decrease in chemotactic activity of the PCcapd towards 10(-8) M N-formylmethionyl-leucyl-phenylalanine and dialysis effluent was observed in LPI patients but not in HPI patients. After one year of treatment, a significantly higher percentage of phagocytosing macrophages in the PCcapd of HPI patients was found when compared to LPI patients. During the year there was an increase of immunophagocytosis of PCcapd independent of PI. In conclusion, the CAPD peritoneal cellular immune system showed signs of both immaturity and activation. The decrease in the yield and in the chemotactic activity of PCcapd suggests an adaptation to the chronic stimulus of the dialysis fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific opsonic activity for staphylococci in peritoneal dialysis effluent during continuous ambulatory peritoneal dialysis

In a prospective study of intraperitoneal opsonins in 30 patients undergoing continuous ambulatory peritoneal dialysis (CAPD), the IgG concentration, the fibronectin concentration, the specific antistaphylococcal antibody level, and the opsonic activity against Staphylococcus epidermidis were measured in peritoneal dialysis effluent from the initiation of CAPD and monthly for 6 months. Significant correlation was found between the four assays, but the interindividual and intraindividual variations were considerable. No statistically significant correlation was observed between susceptibility of the patients to CAPD-related infectious peritonitis and any of the above-mentioned parameters of humoral defense. We conclude that at the present time it is not feasible to use these assays for the establishment of prognosis with regard to peritonitis in CAPD.

Chemotaxis of the peritoneal cells and the detection of a chemo-attractant in the effluent from peritoneal dialysis patients

The migration of peritoneal cells from 25 continuous ambulatory peritoneal dialysis patients and eight healthy women undergoing laparoscopy were studied. Peritoneal cells of continuous ambulatory peritoneal dialysis patients migrated to commonly used chemoattractants, like N-formyl-methionyl-leucyl-phenyl-alanine-methyl- ester and casein, but they also migrated to high concentrations of recombinant interleukin-1 alpha and to endotoxin (lipopolysaccharide). In the peritoneal effluent from continuous ambulatory peritoneal dialysis patients a rather heat stable chemoattractant was found with a molecular weight of 40-200 kDa with an optimal activity at approximately 125 kDa. The chemoattractant is a protein and is not complement factor 5a or interleukin-1 and was only found in peritoneal effluent from continuous ambulatory peritoneal dialysis patients, but not in peritoneal fluid from healthy women undergoing laparoscopy. Therefore, peritoneal dialysis might induce the generation of a chemoattractant. The optimal chemotactic response of peritoneal cells from continuous ambulatory peritoneal dialysis patients to N-formyl-methionyl-leucyl-phenyl-alanine-methyl- ester in medium could be enhanced by replacing the medium by peritoneal effluent. So the chemotaxis of peritoneal cells to the factor in the peritoneal effluent is caused by another mechanism, which might involve different cell surface receptor populations, than the chemotactic response to N-formyl-methionyl-leucyl-phenyl-alanine-methyl-ester.

Monocyte-derived macrophage and alveolar macrophage fibronectin production and cathepsin D activity

Alveolar macrophages are thought to play an important role in ongoing tissue breakdown and repair processes in the normal lung. The secretion and regulation of cathepsin D (important for the final breakdown of collagen) and fibronectin (involved in the healing process) in human peripheral blood monocytes (PBM) and pulmonary alveolar macrophages (PAM) were investigated. Cathepsin D enzyme activity was measured by quantitating the TCA-soluble fragments of [3H]hemoglobin. Freshly isolated PBM contained less cell-associated cathepsin D activity than did freshly isolated PAM (314 +/- 35 micrograms/10(6) cells vs 381 +/- 35 micrograms/10(6) cells, respectively). After 7-10 days in culture, cell-associated enzyme levels in both PBM and PAM were significantly increased (P less than 0.001 for PBM; P less than 0.0001 for PAM). In addition, freshly isolated PAM secreted more cathepsin D than did freshly isolated PBM (5.8 +/- 3.2 micrograms/10(6) cells vs 0.83 +/- 0.83 micrograms/10(6) cells, P less than 0.02). In the presence of LPS (10 micrograms/ml), cell-associated cathepsin D was inhibited in both PBM and PAM. With the addition of gamma-IFN (500 U/ml), both cell-associated and secreted enzyme were increased in freshly isolated and 10-day-cultured PBM and PAM. In parallel studies, fibronectin secretion (by ELISA assay) in both PBM and PAM increased over time in culture. LPS had no effect on PBM or PAM secretion of human fibronectin while gamma-IFN increased PBM and PAM fibronectin levels. Thus, both macrophage cathepsin D activity and fibronectin secretion are increased by gamma-interferon while macrophage cathepsin D activity, but not fibronectin secretion, is decreased by LPS. These studies demonstrate that human macrophage cathepsin D activity is actively modulated by inflammatory mediators and that macrophage mediators of tissue breakdown and repair are not modulated synchronously.

Comparison of peritoneal white blood cell parameters from continuous ambulatory peritoneal dialysis patients with a high or low incidence of peritonitis

The purpose of this study was to determine if there were differences in selected dialysate white blood cells (WBC) parameters between continuous ambulatory peritoneal dialysis (CAPD) patient groups identified as having a high or low incidence of peritonitis. Parameters studied were total peritoneal WBC yield, percentage and absolute number of various WBC types, and expression of WBC receptors known to be involved in normal host defense mechanisms. WBCs were obtained from peritoneal dialysis effluents (overnight dwell), which were collected at monthly intervals for 6 to 8 months from eight CAPD patients--four with a history of high peritonitis incidence (HPI) (more than two episodes in 12 months) and four with a history of low peritonitis incidence (LPI) (no episodes in more than 24 months). Our results demonstrated that there was no significant difference in the overall mean total cell yields or absolute cell counts between the two patient groups. WBC differentials, although differing somewhat among patients, stayed quite stable over time for an individual patient and there was no significant difference between the two patient groups. Analysis of receptors on the peritoneal WBC was performed using flow cytometry and fluorescein-conjugated chemotactic factors (C5a and fMet-Leu-Phe-Lys), as well as monoclonal antibodies specific for Fc receptors and complement receptors, CR1 (CD35) and CR3 (CD11b). Although there was a trend toward increased expression of all these receptors in the HPI patients, there was no significant difference in the fluorescence intensity of peritoneal neutrophils or macrophages that expressed these receptors between the two patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cathepsin D-like activity in neutrophils and monocytes

Monocytes-macrophages and polymorphonuclear leukocytes contain an acid proteolytic enzyme that cleaves tritiated hemoglobin. The monocyte-macrophage-derived enzymatic activity was completely inhibited by pepstatin A, a property of cathepsin D. Monocyte-derived macrophages developed detectable cathepsin D-like activity after 5 days in culture, and this activity coincided with the appearance of other known indicators of macrophage maturation. The cathepsin D activity further increased significantly with time after day 5 of culture. The proteinase activity extracted from neutrophils was only partially inhibitable by pepstatin A, which indicates that this activity is contributed by more than one proteolytic enzyme, including cathepsin D. Cathepsin D activity demonstrated in neutrophils and macrophages may be an important marker of phagocyte function.

Modulation of fibronectin gene expression in human mononuclear phagocytes

Under some conditions, mononuclear phagocytes spontaneously synthesize and release fibronectin, an extracellular matrix glycoprotein with versatile effects on cell-matrix interactions. To gain insight into the processes that modulate the level of fibronectin secretion by these cells, we used monocytes, in vitro matured monocytes and alveolar macrophages as models to compare fibronectin mRNA levels and fibronectin secretion in a variety of circumstances. Using Northern analysis and dot-blot analysis with a 32P-labeled human fibronectin cDNA probe, we evaluated steady-state mRNA levels and a human fibronectin-specific ELISA was used to evaluate fibronectin secretion. In all cases the amounts of fibronectin secreted paralleled fibronectin mRNA levels. Specifically (a) when fibronectin mRNA was undetectable, as in the case of normal blood monocytes, no fibronectin was secreted, but whenever fibronectin mRNA was present, as in normal alveolar macrophages, fibronectin was secreted by the cells; (b) as monocytes matured into macrophages in vitro, the cells began to express fibronectin mRNA and the cells secreted fibronectin; (c) when alveolar macrophages were activated with surface stimuli such as lipopolysaccharide (LPS) or immune complexes, fibronectin mRNA levels decreased and in parallel, the cells secreted less fibronectin; (d) in idiopathic pulmonary fibrosis (IPF), alveolar macrophages contained severalfold more fibronectin mRNA transcripts that normal and the cells spontaneously secreted severalfold more fibronectin than normal; and (e) when IPF alveolar macrophages were placed in culture the fibronectin mRNA levels in the cells decreased with time, and concurrently the amounts of fibronectin produced per unit time continually decreased. The observation of a strict concordance of fibronectin mRNA levels and fibronectin release by mononuclear phagocytes suggests that, at least in many circumstances, fibronectin secretion by mononuclear phagocytes is controlled by steady-state levels of fibronectin mRNA.