Presence Of Surfactant Protein A Research Articles

Impact of Ozone, Sex, and Gonadal Hormones on Bronchoalveolar Lavage Characteristics and Survival in SP-A KO Mice Infected with Klebsiella pneumoniae.

Surfactant protein A (SP-A) plays an important role in innate immunity. The sex-dependent survival of infected SP-A knockout (KO) mice has been observed. Our goal was to study the impact of ozone (O3) and sex, as well as gonadal hormones, on the bronchoalveolar lavage (BAL) readouts and survival, respectively, of Klebsiella pneumoniae-infected SP-A KO mice. Male and female SP-A KO mice were exposed to O3 or filtered air and infected with K. pneumoniae. We studied markers of inflammation and tissue damage at 4, 24, and 48 h, as well as the survival over 14 days, of gonadectomized (Gx) mice implanted with control pellets (CoP) or hormone (5α-dihydrotestosterone (DHT) in female gonadectomized mice (GxF) or 17β-estradiol (E2) in male gonadectomized mice (GxM)). We observed: (1) an increase in neutrophil and macrophage inflammatory protein-2 levels as time progressed post-infection, and O3 exposure appeared to increase this response; (2) an increase in lactate dehydrogenase, total protein, oxidized protein, and phospholipids in response to O3 with no consistent sex differences in studied parameters; and (3) a reduction in survival of the GxM and CoP mice, the GxM and E2 mice, and the GxF and DHT mice but not for the GxF and CoP mice after O3. Without SP-A, (a) sex was found to have a minimal impact on BAL cellular composition and tissue damage markers, and (b) the impact of gonadal hormones on survival was found to involve different mechanisms than in the presence of SP-A.

The plate body: 3D ultrastructure of a facultative organelle of alveolar epithelial type II cells involved in SP-A trafficking

Plate bodies are facultative organelles occasionally described in the adult lungs of various species, including sheep and goat. They consist of multiple layers of plate-like cisterns with an electron dense middle bar. The present study was performed to elucidate the three-dimensional (3D) characteristics of this organelle and its presumed function in surfactant protein A (SP-A) biology. Archived material of four adult goat lungs and PFA-fixed lung samples of two adult sheep lungs were used for the morphological and immunocytochemical parts of this study, respectively. 3D imaging was performed by electron tomography and focused ion beam scanning electron microscopy (FIB-SEM). Immuno gold labeling was used to analyze whether plate bodies are positive for SP-A. Transmission electron microscopy revealed the presence of plate bodies in three of four goat lungs and in both sheep lungs. Electron tomography and FIB-SEM characterized the plate bodies as layers of two up to over ten layers of membranous cisterns with the characteristic electron dense middle bar. The membranes of the plates were in connection with the rough endoplasmic reticulum and showed vesicular inclusions in the middle of the plates and a vesicular network at the sides of the organelle. Immuno gold labeling revealed the presence of SP-A in the vesicular network of plate bodies but not in the characteristic plates themselves. In conclusion, the present study clearly proves the connection of plate bodies with the rough endoplasmic reticulum and the presence of a vesicular network as part of the organelle involved in SP-A trafficking.

Cholesterol-mediated surfactant dysfunction is mitigated by surfactant protein A

The ability of pulmonary surfactant to reduce surface tension at the alveolar surface is impaired in various lung diseases. Recent animal studies indicate that elevated levels of cholesterol within surfactant may contribute to its inhibition. It was hypothesized that elevated cholesterol levels within surfactant inhibit human surfactant biophysical function and that these effects can be reversed by surfactant protein A (SP-A). The initial experiment examined the function of surfactant from mechanically ventilated trauma patients in the presence and absence of a cholesterol sequestering agent, methyl-β-cyclodextrin. The results demonstrated improved surface activity when cholesterol was sequestered in vitro using a captive bubble surfactometer (CBS). These results were explored further by reconstitution of surfactant with various concentrations of cholesterol with and without SP-A, and testing of the functionality of these samples in vitro with the CBS and in vivo using surfactant depleted rats. Overall, the results consistently demonstrated that surfactant function was inhibited by levels of cholesterol of 10% (w/w phospholipid) but this inhibition was mitigated by the presence of SP-A. It is concluded that cholesterol-induced surfactant inhibition can actively contribute to physiological impairment of the lungs in mechanically ventilated patients and that SP-A levels may be important to maintain surfactant function in the presence of high cholesterol within surfactant.

Pulmonary surfactant protein A-induced changes in the molecular conformation of bacterial deep-rough LPS lead to reduced activity on human macrophages

The lung is constantly exposed to immune stimulation by LPS from inhaled microorganisms. A primary mechanism to maintain immune homeostasis is based on anti-inflammatory regulation by surfactant protein A (SP-A), a secreted component of lung innate immunity. The architecture of LPS aggregates is strongly associated with biological activity. We therefore investigated whether SP-A affects the physico-chemical properties of LPS. Determination of the three-dimensional aggregate structure of LPS by small-angle X-ray scattering demonstrated that SP-A induced the formation of multi-lamellar aggregate structures. Determination of the acyl-chain-fluidity of LPS aggregates by Fourier transform infrared (FTIR) spectroscopy showed that the phase transition temperature of LPS was reduced in the presence of SP-A. The phosphate groups at the diglucosamine backbone of LPS represent important functional groups for the bioactivity of LPS. FTIR analysis revealed changes in the vibrational bands νas PO-(2), indicating an interaction of SP-A with the 1-phosphate, but not with the 4'-phosphate. The physico-chemical changes induced by SP-A were associated with up to 90% reduction in LPS-induced TNF-α-production by human macrophages. In conclusion, our data demonstrate that the SP-A/LPS interaction induces conformational changes in LPS aggregates leading to biologically less active structures, thereby providing a new molecular mechanism of immune modulation by SP-A.

Surfactant Protein A Integrates Activation Signal Strength To Differentially Modulate T Cell Proliferation

Pulmonary surfactant lipoproteins lower the surface tension at the alveolar-airway interface of the lung and participate in host defense. Previous studies reported that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that SP-A-mediated modulation of T cell activation depends upon the strength, duration, and type of lymphocyte activating signals. Modulation of T cell signal strength imparted by different activating agents ex vivo and in vivo in different mouse models and in vitro with human T cells shows a strong correlation between strength of signal (SoS) and functional effects of SP-A interactions. T cell proliferation is enhanced in the presence of SP-A at low SoS imparted by exogenous mitogens, specific Abs, APCs, or in homeostatic proliferation. Proliferation is inhibited at higher SoS imparted by different doses of the same T cell mitogens or indirect stimuli such as LPS. Importantly, reconstitution with exogenous SP-A into the lungs of SP-A(-/-) mice stimulated with a strong signal also resulted in suppression of T cell proliferation while elevating baseline proliferation in unstimulated T cells. These signal strength and SP-A-dependent effects are mediated by changes in intracellular Ca(2+) levels over time, involving extrinsic Ca(2+)-activated channels late during activation. These effects are intrinsic to the global T cell population and are manifested in vivo in naive as well as memory phenotype T cells. Thus, SP-A appears to integrate signal thresholds to control T cell proliferation.

Surfactant protein A differentially modulates the functional outcome of T cell activation (39.45)

Abstract The pulmonary surfactant lipoprotein complex lowers the surface tension at the alveolar/airway interface of the lung and participates in pulmonary host defense. Previous studies have shown that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that surfactant proteins may modulate the activation threshold of T cells depending upon the strength of the activation signal. The strength and duration of lymphocyte activation are crucial in determining the fate of responding lymphocytes. Activation of specific signaling pathways, including NFkB, NFAT, STAT and MAPK pathways, determines the quality, magnitude and duration of immune responses, imparts a tunable quality, and essentially constitutes the 'strength of signal' (SoS). This study highlights a differential role of SP-A across multiple modes of T cell activation. Modulation of signal strength imparted by different activating agents ex vivo and in vivo in different mouse models, as well as in vitro with human cells show a strong correlation between strength of signal and functional effects of SP-A interactions. While proliferation is enhanced in the presence of SP-A at low signal strengths, the inhibition reported in the literature is observed at higher SoS. The enhanced proliferation is observed within a kinetic envelope, and is largely absent in SP-A-/- mice, while the inhibition is primarily caused by lack of cell cycle progression, with no effect on cell death or early cytokine production. This is intrinsic to the global T cell population, and is not mediated by proportions of Treg or effector memory cells. Changes in capacitative [Ca++]i flux are likely to be a key component of these phenotypic effects. [Support: NIH HL-68072]

Presence and subcellular localizations of surfactant proteins A and D in human spermatozoa

To investigate the presence of surfactant protein-A (SP-A); molecular weight 34 kDa and surfactant protein-D (SP-D); and molecular weight 43 kDa in human spermatozoa. Prospective, research study. Two universities in Turkey. Semen specimens (n = 10) were obtained from normozoospermic donors. Human sperm were exposed to an anti-human SP-A polyclonal antibody, and monoclonal antibody, to human SP-D protein. Presence of SP-A and SP-D proteins in human beings. Indirect immunofluorescence assays of human sperm indicated the presence of SP-A in the mid piece, the tail, and sometimes at the equatorial region of spermatozoa. A brilliant green light detected SP-D in the tails and acrosome of some sperm. The anti-SP-A antibody detected a single band corresponding to the molecular weight values of 34 kDa in spermatozoa, whereas no band was observed in the negative control. The anti-SP-D antibody showed the expected band at 43 kDa in spermatozoa. This is the first report and a novel finding of the presence of surfactant glycoproteins on human spermatozoa.

Impact of ozone exposure on the phagocytic activity of human surfactant protein A (SP-A) and SP-A variants

Surfactant protein A (SP-A) enhances phagocytosis of Pseudomonas aeruginosa. SP-A1 and SP-A2 encode human (h) SP-A; SP-A2 products enhance phagocytosis more than SP-A1. Oxidation can affect SP-A function. We hypothesized that in vivo and in vitro ozone-induced oxidation of SP-A (as assessed by its carbonylation level) negatively affects its function in phagocytosis (as assessed by bacteria cell association). To test this, we used P. aeruginosa, rat alveolar macrophages (AMs), hSP-As with varying levels of in vivo (natural) oxidation, and ozone-exposed SP-A2 (1A, 1A0) and SP-A1 (6A2, 6A4) variants. SP-A oxidation levels (carbonylation) were measured; AMs were incubated with bacteria in the presence of SP-A, and the phagocytic index was calculated. We found: 1) the phagocytic activity of hSP-A is reduced with increasing levels of in vivo SP-A carbonylation; 2) in vitro ozone exposure of hSP-A decreases its function in a dose-dependent manner as well as its ability to enhance phagocytosis of either gram-negative or gram-positive bacteria; 3) the activity of both SP-A1 and SP-A2 decreases in response to in vitro ozone exposure of proteins with SP-A2 being affected more than SP-A1. We conclude that both in vivo and in vitro oxidative modifications of SP-A by carbonylation reduce its ability to enhance phagocytosis of bacteria and that the activity of SP-A2 is affected more by in vitro ozone-induced oxidation. We speculate that functional differences between SP-A1 and SP-A2 exist in vivo and that the redox status of the lung microenvironment differentially affects function of SP-A1 and SP-A2.

Upregulation of Surfactant Protein A in Chronic Rhinosinusitis

Surfactant protein A (SP-A) is protein that appears to play an important role in mammalian first-line host defense. However, the presence of SP-A in the human paranasal sinus mucosa is not well known. The purpose of this study was to investigate the expression of SP-A protein in human paranasal sinus mucosa and to compare the expression of SP-A mRNA between normal paranasal sinus mucosa and paranasal sinus mucosa with chronic rhinosinusitis. Paranasal sinus mucosa samples from 10 patients who underwent surgery for chronic rhinosinusitis without polyps and 10 normal control subjects were used. Reverse transcriptase polymerase chain reaction was done to detect SP-A mRNA. The expression level of SP-A transcripts was semiquantified with desitometry. Cellular localization of SP-A was sought by using immunohistochemistry. SP-A mRNA and protein were expressed in the human paranasal sinus mucosa. SP-A/GAPDH mRNA ratio in the paranasal sinus mucosa with chronic rhinosinusitis was greater compared with that in normal paranasal sinus mucosa (P<.05). Immunohistochemical staining revealed SP-A immunoreactivity in the epithelial cells and submucosal glands of paranasal sinus mucosa in both control subjects and chronic sinusitis patients. Stronger immunoreactivity was observed in chronic rhinosinusitis mucosa as compared with normal paranasal sinus mucosa. SP-A mRNA and protein are present in both normal and diseased human paranasal sinus mucosa. These results may provide potential targets for novel therapy of chronic rhinosinusitis.

Surfactant proteins A and D enhance the phagocytosis ofChlamydiainto THP-1 cells

Chlamydiae are intracellular bacterial pathogens that infect mucosal surfaces, i.e., the epithelium of the lung, genital tract, and conjunctiva of the eye, as well as alveolar macrophages. In the present study, we show that pulmonary surfactant protein A (SP-A) and surfactant protein D (SP-D), lung collectins involved in innate host defense, enhance the phagocytosis of Chlamydia pneumoniae and Chlamydia trachomatis by THP-1 cells, a human monocyte/macrophage cell line. We also show that SP-A is able to aggregate both C. trachomatis and C. pneumoniae but that SP-D only aggregates C. pneumoniae. In addition, we found that after phagocytosis in the presence of SP-A, the number of viable C. trachomatis pathogens in the THP-1 cells 48 h later was increased approximately 3.5-fold. These findings suggest that SP-A and SP-D interact with chlamydial pathogens and enhance their phagocytosis into macrophages. In addition, the chlamydial pathogens internalized in the presence of collectins are able to grow and replicate in the THP-1 cells after phagocytosis.

Role of Surfactant Protein A in the Innate Host Defense and Autoimmunity

Surfactant protein A (SP-A) is a lung collectin with diverse immunoregulatory activities. SP-A regulates the innate host defense by enhancing phagocytosis of pathogens and modulating the production of nitric oxide and cytokines by immune cells. Additionally, SP-A also modulates the phenotypic and functional properties of the cells of adaptive immune response such as dendritic cells (DCs) and lymphocytes. Bone marrow-derived DCs generated in the presence of SP-A fail to increase lipopolysaccharide-induced upregulation of major histocompatibility complex (MHC) class II and CD86 costimulatory molecule on DCs surface and behaves like “tolerogenic DCs”. SP-A may also induce tolerance by suppressing the proliferation of activated T lymphocytes. Thus, based on immunoregulatory properties of SP-A, it may be employed as a therapeutic agent for the treatment of autoimmune disease and organ transplantation.

Effect of surfactant protein A on granular pneumocyte surfactant secretion in vitro.

Surfactant secretion by lung type II cells occurs when lamellar bodies (LBs) fuse with the plasma membrane and surfactant is released into the alveolar lumen. Surfactant protein A (SP-A) blocks secretagogue-stimulated phospholipid (PL) release, even in the presence of surfactant-like lipid. The mechanism of action is not clear. We have shown previously that an antibody to LB membranes (MAb 3C9) can be used to measure LB membrane trafficking. Although the ATP-stimulated secretion of PL was blocked by SP-A, the cell association of iodinated MAb 3C9 was not altered, indicating no effect on LB movement. FM1-43 is a hydrophobic dye used to monitor the formation of fusion pores. After secretagogue exposure, the threefold enhancement of the number of FM1-43 fluorescent LBs (per 100 cells) was not altered by the presence of SP-A. Finally, there was no evidence of a large PL pool retained on the cell surface through interaction with SP-A. Thus SP-A exposure does not affect these stages in the surfactant secretory pathway of type II cells.

Surfactant protein A enhances Mycobacterium avium ingestion but not killing by rat macrophages.

Mycobacterium avium complex (MAC) is a significant cause of opportunistic infection in patients with acquired immunodeficiency syndrome. Although the major route of entry of MAC is via the gastrointestinal tract, MAC can infect humans through the respiratory tract and eventually encounter alveolar macrophages within the lung. Once in the lung, MAC can potentially interact with surfactant protein A (SP-A), an important component of the pulmonary innate-immune response. Previous work on other pulmonary pathogens including Mycobacterium bovis Bacillus Calmette-Guerin (BCG) suggests that SP-A participates in promoting efficient clearance of these organisms by alveolar macrophages. In the present study, we investigated the role of SP-A in clearance of MAC by cultured rat macrophages. SP-A bound to MAC organisms and enhanced the ingestion of the mycobacteria by macrophages. Infection of macrophages with SP-A-MAC complexes induced the production of nitric oxide (NO) and tumor necrosis factor-alpha. However, intracellular survival of MAC was not altered by preopsonization with SP-A. In addition, inhibitors of inducible NO synthase did not alter MAC clearance. These results suggest that SP-A can bind to and enhance the uptake of MAC by alveolar macrophages, similar to previous findings with BCG and Mycobacterium tuberculosis.However, unlike BCG and other pulmonary pathogens that are cleared effectively in the presence of SP-A via a NO-dependent pathway, macrophage-mediated clearance of MAC is not enhanced by SP-A.

Structural and Functional Aspects of the Collectin SP-A

Surfactant protein A (SP-A), member of the collectin family, is implicated in innate host defense of the lung. SP-A is a "pattern recognition molecule" and interacts with glycoconjugates on the surface of micro-organisms. It protects the lung by interacting with a wide variety of potential pathogens, including viruses, bacteria and fungi. This may result in enhanced killing and clearance by phagocytes. SP-A is a link between the innate and adaptive immune system because it directly affects lymphocyte proliferation and function. Although most extensively studied in the lung, SP-A is found in a number of other sites in the body. The presence of SP-A at these mucosal surfaces, which are in close contact with numerous potentially harmful micro-organisms, supports a more general role for this collectin in mucosal defense.

Neonatal Society program and abstract

To examine whether surfactant protein A (SP-A) in postnatal serum can predict the development of respiratory distress syndrome (RDS), we analyzed the relationship between serum concentrations of SP-A and the risk of RDS using sera from neonates within 24 h after birth. A total of 104 blood samples including 23 samples from newborn infants with RDS were obtained. SP-A content in sera was measured with an enzyme-linked immunosorbent assay system consisting of a standard of native SP-A and two monoclonal antibodies against human SP-A. The level of serum SP-A increased with advancing gestation. Since the mean level of serum SP-A in patients with RDS (3.8 ng/ml) was significantly lower than those without RDS (12.0 ng/ml) (P<0.001), we calculated the diagnostic index values at various cutoff points and chose cutoff values to predict the risk of RDS. Maximum diagnostic value of 85% was obtained at a cutoff point of 3.8 ng/ml (sensitivity 57% and specificity 93%). We also chose a cutoff value of 2.1 ng/ml for definitive diagnosis of RDS, and 8.3 ng/ml for exclusive diagnosis of RDS. The adjusted odds ratios of RDS was significantly elevated when SP-A concentration in serum was under the cutoff values. The presence of SP-A in cord blood serum was also confirmed by immunoblotting analysis. We emphasize the value of SP-A examination in cord blood or postnatal serum from infants who exhibited respiratory difficulties at birth. We believe that our results are consistent with the hypothesis that SP-A is a useful serum marker in predicting the development of RDS.

Pulmonary surfactant protein A in sera for assessing neonatal lung maturation.

To examine whether surfactant protein A (SP-A) in postnatal serum can predict the development of respiratory distress syndrome (RDS), we analyzed the relationship between serum concentrations of SP-A and the risk of RDS using sera from neonates within 24 h after birth. A total of 104 blood samples including 23 samples from newborn infants with RDS were obtained. SP-A content in sera was measured with an enzyme-linked immunosorbent assay system consisting of a standard of native SP-A and two monoclonal antibodies against human SP-A. The level of serum SP-A increased with advancing gestation. Since the mean level of serum SP-A in patients with RDS (3.8 ng/ml) was significantly lower than those without RDS (12.0 ng/ml) (P<0.001), we calculated the diagnostic index values at various cutoff points and chose cutoff values to predict the risk of RDS. Maximum diagnostic value of 85% was obtained at a cutoff point of 3.8 ng/ml (sensitivity 57% and specificity 93%). We also chose a cutoff value of 2.1 ng/ml for definitive diagnosis of RDS, and 8.3 ng/ml for exclusive diagnosis of RDS. The adjusted odds ratios of RDS was significantly elevated when SP-A concentration in serum was under the cutoff values. The presence of SP-A in cord blood serum was also confirmed by immunoblotting analysis. We emphasize the value of SP-A examination in cord blood or postnatal serum from infants who exhibited respiratory difficulties at birth. We believe that our results are consistent with the hypothesis that SP-A is a useful serum marker in predicting the development of RDS.

Localization and Functions of SP-A and SP-D at Mucosal Surfaces

Pulmonary surfactant protein A (SP-A) and D (SP-D), members of the collectin family, are implicated in innate host defense of the lung. Collectins consist of a collagen-like domain and a carbohydrate recognition domain. SP-A and SP-D recognize and interact with glycoconjugates on the surface of microorganisms. They protect the lung by interacting with a wide variety of potential pathogens, including viruses, bacteria, and fungi. This may result in enhanced killing and/or clearance by phagocytes. Although most extensively studied in the lung, both SP-A and SP-D, or proteins closely resembling SP-A and SP-D, are found in a number of other sites in the body and therefore may play a protective role at other sites than the lung. SP-A and SP-D protein and/or mRNA have been detected at various sites of the body: the respiratory tract, the gastrointestinal tract, the middle ear, and in the peritoneal cavity. The presence of SP-A and SP-D at these mucosal surfaces, in close contact with numerous potentially harmful microorganisms, supports a role for these "lung"-collectins in innate mucosal defense. SP-A and SP-D may be important molecules in a threefold innate defense, particularly in the neonatal period between maternally acquired immunity and a fully developed adaptive immune system; the time interval between first exposure to a pathogen and generation of specific antibodies; and states of impaired immune function.

Surfactant protein A suppresses reactive nitrogen intermediates by alveolar macrophages in response to Mycobacterium tuberculosis.

Mycobacterium tuberculosis attaches to, enters, and replicates within alveolar macrophages (AMs). Our previous studies suggest that surfactant protein A (SP-A) can act as a ligand in the attachment of M. tuberculosis to AMs. Reactive nitrogen intermediates (RNIs) play a significant role in the killing of mycobacteria. We have demonstrated that RNI levels generated by AMs were significantly increased when interferon-gamma-primed AMs were incubated with M. tuberculosis. However, the RNI levels were significantly suppressed in the presence of SP-A (10 microg/ml). The specificity of SP-A's effect was demonstrated by the use of F(ab')2 fragments of anti-SP-A monoclonal antibodies and by the use of mannosyl-BSA, which blocked the suppression of RNI levels by SP-A. Furthermore, incubation of deglycosylated SP-A with M. tuberculosis failed to suppress RNI by AMs, suggesting that the oligosaccharide component of SP-A, which binds to M. tuberculosis, is necessary for this effect. These results show that SP-A-mediated binding of M. tuberculosis to AMs significantly decreased RNI levels, suggesting that this may be one mechanism by which M. tuberculosis diminishes the cytotoxic response of activated AMs.

Developmental regulation of the effects of surfactant protein A on phospholipid uptake by fetal rat type II pneumocytes.

Surfactant protein A (SP-A) enhances the uptake of phospholipid by type II cells derived from adult and late gestation fetal rat lung. The present study was performed to examine more fully the developmental biology of the effects of SP-A on phosphatidylcholine (PC) uptake, to determine the effect of SP-A on the cellular location of bound and internalized phospholipid and on the metabolism of internalized phospholipid by morphologically undifferentiated (18-day) and morphologically differentiated (19-day) fetal type II cells. SP-A enhanced uptake almost two-fold in a dose-dependent manner in 19-day fetal cells, but it had no effect on uptake by 18-day fetal cells at any concentration. Stimulation of uptake by 19-day fetal cells was saturable at concentrations above 1 microgram/ml SP-A. Maximal uptake was 1.12 nmol of PC/mg of protein, and the effective concentration that yields 50% maximal response, K phi, was 58.9 ng/ml (84.1 pM). The effect of SP-A on uptake by 19-day fetal cells was detectable as early as 1 min of exposure. Uptake correlated significantly with time both in the absence (r = 0.98, p < 0.001) and presence of 5 micrograms/ml SP-A (r = 0.979, p < 0.001). The rate of uptake in the presence of SP-A (0.019 +/- 0.002 nmol of PC/mg of protein/min) was twice the rate of uptake in controls (0.009 +/- 0.001 nmol of PC/mg of protein/min). SP-A had no effect on binding to plasma membranes and uptake of phospholipid into lamellar bodies by 18-day fetal cells. On the other hand, SP-A significantly enhanced binding of dipalmitoyl phosphatidylcholine to plasma membranes (two- to threefold) and uptake into lamellar bodies (threefold) of 19-day fetal cells. SP-A caused a significant reduction in the degradation of internalized phospholipid by differentiated fetal type II cells. Based on the lack of effect of exogenous SP-A on 18-day fetal cells, we conclude that the response to SP-A is under developmental control. SP-A enhances the initial binding to the plasma membranes of fetal type II cells and subsequent internalization into the lamellar bodies. This effect is associated with a protection of internalized phospholipid from metabolic degradation. Both of these processes are developmentally regulated during the transition from the canalicular to the saccular phase of lung development.

Expression of hydrophilic surfactant proteins by mesentery cells in rat and man.

Human peritoneal dialysis effluent (PDE) contains a phosphatidylcholine-rich compound similar to the surfactant that lines lung alveoli. This material is secreted by mesothelial cells. Lung surfactant is also characterized by four proteins essential to its function. After having long been considered as lung-specific, some of them have been found in gastric and intestinal epithelial cells. To explore further the similarity between lung and peritoneal surfactants, we investigated whether mesothelial cells also produce surfactant proteins. We used rat transparent mesentery, human visceral peritoneum biopsies and PDE. Surfactant proteins were searched for after one- and two-dimensional SDS/PAGE and Western blotting. On a one-dimensional Western blot, bands at 38 and 66 kDa in rat mesentery, and at 38 and 66 kDa in human peritoneal mesothelial cells (in vivo and in vitro) and PDE, corresponded to monomeric and dimeric forms of lung surfactant protein A (SP-A). On two-dimensional Western blots, the 32 and 38 kDa spots in mesentery and PDE localized at the acidic pH appropriate to the SP-A monomer's isoelectric point. SP-D was also identified at the same 43 kDa molecular mass as in lung. SP-B was not detected in mesenteric samples. Expression of SP mRNA species was also assessed by reverse transcriptase-PCR, which was performed with specific primers of surfactant protein cDNA sequences. With primers of SP-A and SP-D, DNA fragments of the same size were amplified in lung and mesentery, indicating the presence of SP-A and SP-D mRNA species. These fragments were labelled by appropriate probes in a Southern blot. No amplification was obtained for SP-B. These results show that mesentery cells produce SP-A and SP-D, although they are of embryonic origin (mesodermal) and are different from those of the lung and digestive tract (endodermal) that secrete these surfactants.