Genetic mutations in surfactant protein C are a rare cause of sporadic cases of IPF.

BACKGROUND: While idiopathic pulmonary fibrosis (IPF) is one of the most common forms of interstitial lung disease, the aetiology of IPF is poorly understood. Familial cases of pulmonary fibrosis suggest a genetic basis for some forms of the disease. Recent reports have linked genetic mutations in surfactant protein C (SFTPC) with familial forms of pulmonary fibrosis, including one large family in which a number of family members were diagnosed with usual interstitial pneumonitis (UIP), the pathological correlate to IPF. Because of this finding in familial cases of pulmonary fibrosis, we searched for SFTPC mutations in a cohort of sporadic cases of UIP and non-specific interstitial pneumonitis (NSIP). METHODS: The gene for SFTPC was sequenced in 89 patients diagnosed with UIP, 46 patients with NSIP, and 104 normal controls. RESULTS: Ten single nucleotide polymorphisms in the SFTPC sequence were found in IPF patients and not in controls. Only one of these created an exonic change resulting in a change in amino acid sequence. In this case, a T to C substitution resulted in a change in amino acid 73 of the precursor protein from isoleucine to threonine. Of the remaining polymorphisms, one was in the 5' UTR, two were exonic without predicted amino acid sequence changes, and six were intronic. One intronic mutation suggested a potential enhancement of a splicing site. CONCLUSIONS: Mutations in SFTPC are identified infrequently in this patient population. These findings indicate that SFTPC mutations do not contribute to the pathogenesis of IPF in the majority of sporadic cases.

Transforming growth factor-beta induces collagen synthesis without inducing IL-8 production in mesothelial cells.

Conventional pleurodesing agents often provoke acute pleural inflammation followed by fibrosis. The inflammation frequently causes pain and fever. Transforming growth factor (TGF)-beta is a pro-fibrotic but anti-inflammatory cytokine. Intrapleural TGF-beta2 administration produces effective pleurodesis in animals, but its effects on mesothelial cells are unknown. The authors hypothesised that, unlike conventional pleurodesing agents, TGF-beta2 can induce collagen synthesis without stimulating pleural inflammation. In the in vitro studies, TGF-beta2, talc and doxycycline were administered to rabbit mesothelial cells for 24 h. These agents were also injected intrapleurally in rabbits and the induced pleural fluids collected at 24 h. TGF-beta2 was as potent as talc and doxycycline in upregulating mesothelial cell collagen expression. Talc and doxycycline both induced significant increases in interleukin (IL)-8 production from mesothelial cells in vitro and in rabbit pleural fluids in vivo. TGF-beta2, however, did not stimulate mesothelial cell IL-8 release in vitro and induced a dose-dependent suppression of pleural fluid IL-8. Pleural fluid IL-8 levels correlated significantly with leukocyte and lactate dehydrogenase concentrations in the fluids. In summary, transforming growth factor-beta was a potent inducer of mesothelial cell collagen synthesis. Unlike talc and tetracycline, which provoked pleural inflammation, transforming growth factor-beta2 suppressed pleural inflammation in vivo. Transforming growth factor-beta2 can produce effective pleural fibrosis without necessitating acute pleural inflammation.

Transcription of a single mannose receptor gene by macrophage and retinal pigment epithelium.

To determine if the macrophage mannose receptor transcript is present in mouse, rat, pig, and human retinal pigment epithelium (RPE), primary cultures and/or freshly dissected retinal pigment epithelium from four different species were used to isolate total RNA. RT-PCR was used to amplify segments of the macrophage mannose receptor from each sample. Amplified products were sequenced and compared with known sequences of the macrophage mannose receptor. Macrophage mannose receptor transcripts were identified in all RPE samples. Comparison between sequences identified in RPE with macrophage sequences from the same species revealed 100% identity. Sequence homology between the different species was 74% or greater. These data are consistent with the transcription of a single mannose receptor gene by these two phagocytic cell types.

Mutation in the gene for bone morphogenetic protein receptor II as a cause of primary pulmonary hypertension in a large kindred.

BACKGROUND: Most patients with primary pulmonary hypertension are thought to have sporadic, not inherited, disease. Because clinical disease develops in only 10 to 20 percent of persons carrying the gene for familial primary pulmonary hypertension, we hypothesized that many patients with apparently sporadic primary pulmonary hypertension may actually have familial primary pulmonary hypertension. METHODS: In a study conducted over 20 years, we developed a registry of 67 families affected by familial primary pulmonary hypertension. Through patient referrals, extensive family histories, and correlation of family pedigrees, we discovered shared ancestry among five subfamilies. We established the diagnosis of primary pulmonary hypertension by direct evaluation of patients and review of autopsy material and medical records. We assessed some family members for mutations in the gene encoding bone morphogenetic protein receptor II (BMPR2), which has recently been found to cause familial primary pulmonary hypertension. RESULTS: We linked five separately identified subfamilies that included 394 known members spanning seven generations, which were traced back to a founding couple in the mid-1800s. Familial primary pulmonary hypertension has been diagnosed in 18 family members, 12 of whom were first thought to have sporadic disease. The conditions of 7 of the 18 were initially misdiagnosed as other cardiopulmonary diseases. Six members affected with familial primary pulmonary hypertension and 6 of 10 at risk for carriage have been undergone genotype analysis, and they have the same mutation in BMPR2, a transversion of thymine to guanine at position 354 in exon 3. CONCLUSIONS: Many cases of apparently sporadic primary pulmonary hypertension may be familial. Failure to detect familial primary pulmonary hypertension results from incomplete expression within families, skipped generations, and incomplete family pedigrees. The recent discovery of mutations in BMPR2 should make it possible to identify those with susceptibility to disease.

Transforming growth factor beta2 induced pleurodesis is not inhibited by corticosteroids.

BACKGROUND: Talc and tetracyclines induce pleurodesis by directly injuring the pleura. The injury results in intense inflammation which subsequently leads to fibrosis. Corticosteroids can inhibit talc pleurodesis by reducing the inflammatory process. We hypothesised that transforming growth factor beta2 (TGFbeta2), a fibrogenic cytokine with immunomodulatory functions, could induce effective pleurodesis without generating significant pleural inflammation and therefore remain effective despite co-administration of corticosteroids. METHODS: Thirty rabbits were divided into two groups. Rabbits in the steroid group received weekly intramuscular injections of triamcinolone diacetate (0.8 mg/kg). Ten rabbits in each group were given 5.0 microg TGFbeta2 intrapleurally via a chest tube while the remaining five received 1.7 microg TGFbeta2. Pleurodesis was graded macroscopically after 14 days from 1 (none) to 8 (>50% symphysis). RESULTS: TGFbeta2 produced excellent pleurodesis at both 5.0 microg and 1.7 microg doses. The pleural effusions produced after the injection were low in all inflammatory markers. No significant differences were seen between the steroid group and controls in macroscopic pleurodesis scores (7.2 (1.3) v 7.1 (1.2)), levels of inflammatory markers in the pleural fluids (leucocyte 1107 (387)/mm(3) v 1376 (581)/mm(3); protein 3.1 (0.3) mg/dl v 2.9 (0.3) mg/dl, and LDH 478 (232) IU/l v 502 (123) IU/l), and the degree of microscopic pleural fibrosis and pleural inflammation. CONCLUSIONS: TGFbeta2 can induce effective pleurodesis and remains effective in the presence of high dose parenteral corticosteroids.

The many faces of transforming growth factor-beta in pleural diseases.

Transforming growth factor (TGF)-beta is responsible for critical regulatory functions in many physiologic and pathologic processes. Emerging evidence suggests that these roles also apply to a multitude of pleural diseases. Both mesothelial cells and infiltrating cells in the pleural space can produce TGFbeta, and elevated TGFbeta concentrations have been found in pleural effusions and in pleural tissues during disease processes. Recent animal studies have suggested that TGFbeta can induce significant pleurodesis and probably plays a central role in the pathogenesis of pleural fibrosis. Paradoxically, TGFbeta may also stimulate increased pleural fluid formation, in part by inducing the production of vascular endothelial growth factor. TGFbeta also participates in the regulation of pleural inflammation and cell proliferation. Further research into the roles of TGFbeta in the pathogenesis of various pleural diseases is needed and may lead to the development of novel treatment strategies.

Transforming growth factor-beta2 induces pleurodesis significantly faster than talc.

Transforming growth factor-beta2 (TGF-beta2) has recently been shown to produce effective pleurodesis in rabbits. Conventional pleurodesing agents such as talc act by inducing pleural injury, which results in acute inflammation and fibrosis. TGF-beta2 is a profibrotic cytokine capable of producing fibrosis without inducing significant pleural inflammation. We hypothesize that intrapleural administration of TGF-beta2 would (1) produce an effective pleurodesis faster; (2) stimulate more collagen deposition, and (3) induce less inflammation when compared with intrapleural injection of talc. Thirty rabbits were divided into two groups and given either TGF-beta(2) (1.7 microg) or talc slurry (400 mg/kg) via a chest tube. Five rabbits from each group were killed at Days 1, 4, and 7. Gross pleurodesis was graded from 1 (none) to 8 (complete symphysis). The microscopic pleural inflammation and fibrosis were graded from 0 to 4. Pleural thickening and the total area of collagen deposition were compared. Intrapleural injection of TGF-beta2 produced effective pleurodesis within 7 d (median pleurodesis score = 7 at Day 7). At Day 7, TGF-beta2 induced significantly more collagen deposition (19.4 +/- 19.6% versus 4.6 +/- 2.9% of total area of pleura at Day 7), higher pleural fibrosis score (3.0 +/- 1.0 versus 1.8 +/- 0.5), and pleural thickness (286 +/- 191 versus 85 +/- 37 microm) than did talc. There was no difference in the degree of pleural inflammation between the two groups at Day 7 (2.6 +/- 0.9 for TGF-beta2 versus 2.4 +/- 0.6 for talc) or at any other time points. In conclusion, the intrapleural administration of TGF-beta2 produced excellent pleurodesis in rabbits at a rate faster than talc slurry and all other pleurodesing agents investigated before. TGF-beta2 stimulated more collagen deposition without inducing excess inflammation when compared with talc slurry. TGF-beta2 may have advantages over talc slurry in the management of recurrent pleural effusion and pneumothorax.

BMPR2 haploinsufficiency as the inherited molecular mechanism for primary pulmonary hypertension.

Primary pulmonary hypertension (PPH) is a potentially lethal disorder, because the elevation of the pulmonary arterial pressure may result in right-heart failure. Histologically, the disorder is characterized by proliferation of pulmonary-artery smooth muscle and endothelial cells, by intimal hyperplasia, and by in situ thrombus formation. Heterozygous mutations within the bone morphogenetic protein type II receptor (BMPR-II) gene (BMPR2), of the transforming growth factor beta (TGF-beta) cell-signaling superfamily, have been identified in familial and sporadic cases of PPH. We report the molecular spectrum of BMPR2 mutations in 47 additional families with PPH and in three patients with sporadic PPH. Among the cohort of patients, we have identified 22 novel mutations, including 4 partial deletions, distributed throughout the BMPR2 gene. The majority (58%) of mutations are predicted to lead to a premature termination codon. We have also investigated the functional impact and genotype-phenotype relationships, to elucidate the mechanisms contributing to pathogenesis of this important vascular disease. In vitro expression analysis demonstrated loss of BMPR-II function for a number of the identified mutations. These data support the suggestion that haploinsufficiency represents the common molecular mechanism in PPH. Marked variability of the age at onset of disease was observed both within and between families. Taken together, these studies illustrate the considerable heterogeneity of BMPR2 mutations that cause PPH, and they strongly suggest that additional factors, genetic and/or environmental, may be required for the development of the clinical phenotype.

Comparing transforming growth factor beta-2 and fibronectin as pleurodesing agents.

BACKGROUND: We have recently demonstrated that transforming growth factor beta-2 (TGF-beta2) can produce effective pleurodesis. Whether this effect can be reproduced by the use of its downstream proteins is not known. This study compared the effectiveness of TGF-beta2 and fibronectin in inducing pleurodesis in rabbits. METHODOLOGY: New Zealand white rabbits (1.5-2.0 kg) were given 1.7 microg of TGF-beta2 (n=5) or 2.0 mg of cellular fibronectin (n=4) intrapleurally via a chest tube. The induced pleural fluid was collected and analyzed. The rabbits were sacrificed after 14 days. The pleurodesis was graded macroscopically from 1 (none) to 8 (symphysis > 50%). RESULTS: All rabbits in the TGF-beta2 group developed effective pleurodesis while none in the fibronectin group had scores > 2 (pleurodesis scores 7.0 +/- 0.6 vs 1.3 +/- 0.3, P < 0.001). Rabbits that received TGF-beta2 produced large amounts of pleural fluid initially (< 4 days). Microscopically, the pleura of rabbits in the TGF-beta2 group showed prominent spindle cell proliferation and collagen deposition, but no significant inflammation or mesothelial proliferation. Pleural tissues of rabbits in the fibronectin group had occasional thin collagen deposits only. The intrapleural administration of 2.0 mg of fibronectin, a downstream product of TGF-beta, did not induce effective pleurodesis, as did the intrapleural administration of TGF-beta2. CONCLUSIONS: The present study suggests that the mechanism by which TGF-beta2 induces pleurodesis is not predominantly dependent on the production of fibronectin.

Transforming growth factor beta(2) (TGF beta(2)) produces effective pleurodesis in sheep with no systemic complications.

BACKGROUND: We have recently shown that transforming growth factor (TGF)beta(2) induces effective pleurodesis in rabbits. However, rabbits have a thin pleura while humans have a thick visceral pleura. The effect of intrapleural administration of TGF beta(2) in animals with a thick pleura and its associated systemic effects have not been investigated. This study was undertaken (1) to develop a new animal model for the study of pleurodesis using sheep which have a thick pleura resembling that of humans; (2) to study the efficacy of TGF beta(2) as a pleurodesis agent in the sheep model; and (3) to assess whether histological changes occur in extrapulmonary organs after intrapleural administration of TGF beta(2). METHODS: Twelve sheep were divided into four groups and were given a single intrapleural injection of TGF beta(2) in a concentration of 1.0 microg/kg, 0.5 microg/kg, 0.25 microg/kg or 0.125 microg/kg to the right pleural cavity via a chest tube. The left pleural cavity served as the control. Any pleural fluid that accumulated after the intrapleural TGF beta(2) injection was collected and analysed. The degree of pleurodesis was graded from 1 (no adhesions) to 8 (complete symphysis >50% of chest wall) at day 14 when the sheep were killed. Biopsy specimens were taken from the lungs and extrapulmonary organs. RESULTS: All sheep that received > or = 0.25 microg/kg TGF beta(2) developed excellent pleurodesis (score = 8) while those that received 0.125 microg/kg had a median score of 6. The pleurodesis score did not exceed 2 in the control (left) side of any sheep. Sheep receiving > or = 0.50 microg/kg TGF beta(2) developed large exudative pleural effusions while those receiving a lower dose did not. The production of effusions neither hindered nor was necessary for inducing pleurodesis. There were no significant fibrotic changes in any of the extrapulmonary organs. CONCLUSION: Intrapleural injection of 0.25-1.0 microg/kg TGF beta(2) produces excellent pleurodesis in a new sheep model with no evidence of extrapulmonary fibrosis.

Heterozygous germline mutations in BMPR2, encoding a TGF-beta receptor, cause familial primary pulmonary hypertension.

Primary pulmonary hypertension (PPH), characterized by obstruction of pre-capillary pulmonary arteries, leads to sustained elevation of pulmonary arterial pressure (mean >25 mm Hg at rest or >30 mm Hg during exercise). The aetiology is unknown, but the histological features reveal proliferation of endothelial and smooth muscle cells with vascular remodelling (Fig. 1). More than one affected relative has been identified in at least 6% of cases (familial PPH, MIM 178600). Familial PPH (FPPH) segregates as an autosomal dominant disorder with reduced penetrance and has been mapped to a locus designated PPH1 on 2q33, with no evidence of heterogeneity. We now show that FPPH is caused by mutations in BMPR2, encoding a TGF-beta type II receptor (BMPR-II). Members of the TGF-beta superfamily transduce signals by binding to heteromeric complexes of type I and II receptors, which activates serine/threonine kinases, leading to transcriptional regulation by phosphorylated Smads. By comparison with in vitro studies, identified defects of BMPR-II in FPPH are predicted to disrupt ligand binding, kinase activity and heteromeric dimer formation. Our data demonstrate the molecular basis of FPPH and underscore the importance in vivo of the TGF-beta signalling pathway in the maintenance of blood vessel integrity.

A single intrapleural injection of transforming growth factor-beta(2) produces an excellent pleurodesis in rabbits.

The purpose of the present study was to determine whether the intrapleural injection of transforming growth factor beta(2) (TGF-beta(2)) would produce a pleurodesis in rabbits. Single intrapleural injections of TGF-beta(2) at doses of 5.00 microg (n = 12), 1.67 microg (n = 10), 0.50 microg (n = 10), or 0.167 microg (n = 4), or of the parenteral buffer alone (n = 5) were given in a volume of 2 ml to New Zealand white rabbits. Chest tubes were left in place for at least 72 h. Pleural fluid was aspirated at 24-h intervals and was measured and subjected to chemical analysis. The animals were killed 14 d after the injection. The intrapleural injection of TGF-beta(2) resulted in a dose-dependent pleurodesis (on a scale of 0 to 4, where 0 = no pleurodesis and 4 = complete pleurodesis) with mean scores of 3.6, 2.6, 1.5, 0.7, and 0.3 for the groups that received 5.0, 1.67, 0.50, and 0.167 microg of TGF-beta(2) and buffer alone, respectively. Intrapleural injection of the larger doses of TGF-beta(2) resulted in the formation of a large amount of pleural fluid. The fluid had a significantly lower white blood cell (WBC) count and lactate dehydrogenase (LDH) level than did the fluid that results from the intrapleural injection of 10 mg/kg doxycycline or 400 mg/kg talc slurry. On the basis of this study we conclude that a single intrapleural injection of TGF-beta(2) induces pleurodesis in a dose-dependent manner. A dose of 5.0 microg produced satisfactory pleurodesis in almost all of the rabbits so treated. Larger doses of TGF-beta(2) induced larger pleural effusions with relatively low pleural fluid WBC counts and LDH levels. The ability of TGF-beta to produce a pleurodesis in patients with recurrent pleural effusions or pneumothorax should be investigated. A single intrapleural injection of TGF-beta(2) may produce a pleurodesis both safely and painlessly.

Transfection of nasal mucosa with a normal alpha1-antitrypsin gene in alpha1-antitrypsin-deficient subjects: comparison with protein therapy.

We sought to determine whether a normal alpha1-antitrypsin (AAT) gene could be expressed in respiratory epithelium and whether local expression would have antiinflammatory effects. In an unblinded study, we delivered a normal AAT gene in a plasmid-cationic liposome complex to one nostril of each of five subjects with AAT deficiency; the other, untreated nostril served as a control. AAT protein concentration in nasal lavage fluid (NALF) increased in the transfected nostril (TN), but not in the control nostril (CN), of every subject, peaking on day 5 at levels about one-third normal (baseline CN, 4.1 +/- 1.2 microg/mg of protein; baseline TN, 4.3 +/- 1.3; day 5 CN, 4.0 +/- 0.5 [p = NS versus baseline]; day 5 TN, 9.0 +/- 1.7 [p < 0.5 versus baseline]); isoelectric focusing identified the transgene-generated protein (M) in the only two patients in whom the measurement was possible. The reverse transcriptase-polymerase chain reaction (RT-PCR), performed on NALF from TN and CN of four of the five subjects, was positive for transgene message in TN in all cases and negative in NALF from CN except for one time point in one subject. Interleukin 8 (IL-8) concentrations in NALF were elevated at baseline (normal [N = 10] = 2.5 +/- 0.5 ng/mg of protein; baseline TN = 5.5 +/- 0.8, p < 0.05 versus normal) and decreased after AAT transfection (TN = 2.9 +/- 0.6, p < 0.05 versus baseline) but not in the control nostril (CN = 6.5 +/- 2.2, p = NS versus baseline). NALF samples taken from four of the patients while receiving intravenous AAT protein showed normal concentrations of AAT, but IL-8 concentrations (10.5 +/- 4.2 ng/mg of protein, p = NS versus baseline) were not decreased from baseline. We conclude that plasmid-cationic liposome delivery of a normal AAT gene to the respiratory epithelium of deficient patients produces potentially therapeutic local AAT concentrations and that AAT gene therapy, unlike AAT protein therapy, is antiinflammatory.

Translation of two nested genes in bacteriophage P4 controls immunity-specific transcription termination.

In phage P4, transcription of the left operon may occur from both the constitutive PLE promoter and the regulated PLL promoter, about 400 nucleotides upstream of PLE. A strong Rho-dependent termination site, timm, is located downstream of both promoters. When P4 immunity is expressed, transcription starting at PLE is efficiently terminated at timm, whereas transcription from PLL is immunity insensitive and reads through timm. We report the identification of two nested genes, kil and eta, located in the P4 left operon. The P4 kil gene, which encodes a 65-amino-acid polypeptide, is the first translated gene downstream of the PLE promoter, and its expression is controlled by P4 immunity. Overexpression of kil causes cell killing. This gene is the terminal part of a longer open reading frame, eta, which begins upstream of PLE. The eta gene is expressed when transcription starts from the PLL promoter. Three likely start codons predict a size between 197 and 199 amino acids for the Eta gene product. Both kil and eta overlap the timm site. By cloning kil upstream of a tRNA reporter gene, we demonstrated that translation of the kil region prevents premature transcription termination at timm. This suggests that P4 immunity might negatively control kil translation, thus enabling transcription termination at timm. Transcription starting from PL proceeds through timm. Mutations that create nonsense codons in eta caused premature termination of transcription starting from PLL. Suppression of the nonsense mutation restored transcription readthrough at timm. Thus, termination of transcription from PLL is prevented by translation of eta.

PU.1 and USF are required for macrophage-specific mannose receptor promoter activity.

In the current study we report the isolation of 854 base pairs of the rat mannose receptor promoter. Analysis of the sequence revealed one Sp1 site, three PU.1 sites, and a potential TATA box (TTTAAA) 33 base pairs 5' of the transcriptional start site. The tissue specificity of the promoter was determined using transient transfections. The promoter was most active in the mature macrophage cell line NR8383 although the promoter also showed activity in the monocytic cell line RAW. No activity was observed in pre-monocytic cell lines or epithelial cell lines. Mutation of the TTTAAA sequence to TTGGAA resulted in a 50% decrease in activity in transient transfection assays suggesting that the promoter contains a functional TATA box. Using electrophoretic mobility shift assays and mutagenesis we established that the transcription factors Sp1, PU.1, and USF bound to the mannose receptor promoter, but only PU.1 and USF contributed to activation. Transient transfections using a dominant negative construct of USF resulted in a 50% decrease in mannose receptor promoter activity, further establishing the role of USF in activating the rat mannose receptor promoter. Comparison of the rat, mouse, and human sequence demonstrated that some binding sites are not conserved. Gel shifts were performed to investigate differences in protein binding between species. USF bound to the rat and human promoter but not to the mouse promoter, suggesting that different mechanisms are involved in regulation of mannose receptor expression in these species. From these results we conclude that, similar to other myeloid promoters, transcription of the rat mannose receptor is regulated by binding of PU.1 and a ubiquitous factor at an adjacent site. However, unlike other myeloid promoters, we have identified USF as the ubiquitous factor, and demonstrated that the promoter contains a functional TATA box.

Characterization of a rat alveolar macrophage cell line that expresses a functional mannose receptor.

The mannose receptor is a single polypeptide transmembrane glycoprotein expressed on the surface of macrophages that binds and internalizes soluble and particulate ligands. Physiological ligands for this receptor are pathogens, such as mycobacteria, and extracellular acid hydrolases and peroxidases. Expression of the mannose receptor is tightly linked to the functional state of the macrophage: the receptor appears during differentiation, is increased by macrophage deactivating agents, and is reduced in the presence of macrophage activating agents. Studies of the mechanisms underlying these regulatory processes have been hampered by the lack of a stable cell line that expresses a functional and appropriately regulated mannose receptor. In this study we describe expression and modulation of the mannose receptor by the rat alveolar cell line NR8383. Similar amounts of the mannose receptor ligand horseradish peroxidase were internalized by both NR8383 cells and alveolar macrophages. In addition, NR8383 cells expressed immunoreactive mannose receptor protein and mannose receptor mRNA as detected by Northern analysis. Regulation studies showed that mannose receptor expression was regulated at the levels of activity, protein, and mRNA in NR8383 cells similarly to regulation in primary rat macrophages. In addition, NR8383 cells could be successfully transfected with a luciferase reporter gene, providing the transfectable, mannose receptor-positive macrophage cell line. These results support the hypothesis that NR8383 cells potentially represent the best current macrophage cell line for studying various aspects of macrophage function, and are particularly critical in studies of regulation of the mannose receptor, a key receptor in host defense and immune regulation.

Ingestion of Candida albicans down-regulates mannose receptor expression on rat macrophages.

The frequency of infection and death due to various Candida species has increased steadily during the past decade, with mucocutaneous candidal infections as a common problem in the immunocompromised host. Mononuclear phagocytes are important in phagocytosis of this organism. In areas where there are low levels of opsonins, the macrophage-specific mannose receptor plays a dominant role in mediating Candida albicans ingestion. Following receptor-mediated infection, the host macrophage produces inflammatory cytokines and mediators that lead to ultimate killing of the invading Candida. Infection of macrophages by pathogens often leads to altered function that might effect their subsequent host defense properties. For example, function of both the complement receptor type 3 and the mannose receptor are down-regulated following exposure to pathogens or pathogen-derived products. In the current study, we have examined the down-regulation of mannose receptor expression following Candida infection and have investigated possible mechanisms that might be involved. Mannose receptor activity was decreased following 24 h postinfection with Candida. Both tumor necrosis factor and nitric oxide were produced during the infection, and inhibition of the these mediators partially blocked the effect on the receptor. Infection with Candida also inhibited the ability of dexamethasone to up-regulate mannose receptor expression. Finally, mannose receptor protein turnover was accelerated in Candida-infected macrophages. We conclude that Candida down-regulates one of the receptors involved in its internalization through a combination of production of modulatory molecules and enhanced receptor degradation. These results support the hypothesis that pathogens that infect macrophages have the ability to alter the phagocytic pathways available for subsequent host defense.