Biomedical subjects

E Crouch

Publications and source records attributed to E Crouch.

At least 19 recordsLinked to original sources

PubMed1997

A DNA polymerase alpha accessory protein exhibits structural and functional similarities to SV40 large tumor antigen.

Untransformed cells have been proposed to require a protein homologous to SV40 large tumor antigen (TAg) which functions as a component of the replicase complex during the initiation of DNA synthesis. By definition, this should be a phosphoprotein which interacts with the retinoblastoma protein (pRb) in G0 or early G1, and is capable of binding to and potentiating the activity of DNA polymerase alpha (pol alpha). This protein should also be an ATP-dependent helicase which interacts with the single-stranded DNA (ssDNA) binding protein, RP-A. Because of these requirements, a TAg homologous protein could be expected to contain epitopes with amino acid sequences similar to those of TAg at critical functional sites, such as ATP, pRb and pol alpha binding sites. TAg and a putative cellular homolog of TAg, DNA pol alpha accessory protein (alpha AP), were compared for pRb and pol alpha interaction, and for immunological identity. The analyses utilized immunoaffinity-purified TAg and pRb from a baculovirus expression system, and DNA pol alpha/primase and alpha AP chromatographically isolated from a mouse lymphocytic leukemia cell line. Monoclonal antibodies specific for the pol alpha or pRb binding sites on TAg interacted with alpha AP strongly enough to be employed for immunoaffinity purification of alpha AP. Anti-pRb and anti-TAg reciprocally coimmunoprecipitated pRb bound to TAg and pRb bound to alpha AP. The functional consequences of pol alpha interaction with TAg or alpha AP in the presence or absence of pRb was determined using pol alpha nucleotide incorporation assays. alpha AP exhibited the capacity to stimulate pol alpha activity, a capacity which was diminished in the presence of pRb. Lastly, TAg and alpha AP independently co-purified with pol alpha through a multi-step chromatographic protocol. These data indicate that a pol alpha accessory protein, alpha AP, exhibits functional and immunological similarities to SV40 TAg, suggest that alpha AP is involved in regulation of the initiation of DNA synthesis, and support the proposal that alpha AP may be a normal cell protein homologous to SV40 large T antigen.

Animals↗

PubMed1996

Neutrophil deactivation by influenza A viruses: mechanisms of protection after viral opsonization with collectins and hemagglutination-inhibiting antibodies.

Bacterial superinfections are a major cause of morbidity and mortality during influenza A virus (IAV) epidemics. Depression of phagocyte functions resulting from attachment of the IAV hemagglutinin (HA) to cell surface sialo-glycoproteins is a likely contributory cause of these infections. We have proposed that the group of collagenous lectins (termed collectins) present in blood and pulmonary surfactant play a role in initial host defense against IAV. We used here several recombinant human surfactant protein D (RhSP-D) preparations to determine the mechanism through which opsonization of IAV with collectins protects neutrophils against the deactivating effects of IAV on cellular respiratory burst responses in vitro. RhSP-D was markedly more potent than antibodies that inhibited viral hemagglutination activity (anti-HA antibodies) at protecting neutrophils in this assay. Unlike the anti-HA antibodies, RhSP-D was protective at concentrations that minimally inhibited viral hemagglutination activity. Two related features of SP-D--the degree of multimerization and the ability to cause aggregation of IAV particles--were critical determinants of the ability of SP-D to protect neutrophils against deactivation. Similarly SP-D-induced viral aggregate formation resulted in enhanced IAV binding to neutrophils and potentiated the ability of the virus itself to trigger neutrophil respiratory burst responses. In contrast to the case of IAV-antibody complexes, SP-D-IAV complexes attached to and activated neutrophils through a neuraminidase-sensitive mechanism (ie, similar to unopsonized IAV). These results indicate that collectin-mediated viral aggregation per se may be an important host defense mechanism not only by virtue of reducing the number of infectious viral particles, but also by promoting phagocyte responsiveness.

Animals↗

PubMed1996

Interactions of recombinant human pulmonary surfactant protein D and SP-D multimers with influenza A.

To further study the structure and function of surfactant protein D (SP-D), recombinant human SP-D (rhSP-D) was isolated from the culture medium of Chinese hamster ovary (CHO)-K1 cells stably transfected with a full-length hSP-D cDNA. Although a significant fraction of the secreted rhSP-D was recovered as dodecamers similar to recombinant rat SP-D (rrSP-D), a major fraction accumulated as multimers of dodecamers indistinguishable from human proteinosis SP-D. As previously shown for the rat protein, rhSP-D agglutinated specific strains of influenza A virus (IAV), inhibited viral hemagglutinin activity, and protected neutrophils (PMN) from deactivation by IAV. However, the potency of rhSP-D multimers was severalfold greater than for purified dodecamers, comparable to natural, proteinosis hSP-D. Although rhSP-D multimers were also more potent than the serum collectins in mediating viral aggregation and protection of PMN, they were less potent than conglutinin in inhibiting infectivity in vitro. These studies establish that the propensity of hSP-D to form multimers of dodecamers is determined by its primary structure and demonstrate carbohydrate recognition domain valency-dependent interactions of SP-D with IAV.

Animals↗

PubMed1996

Localization of type I procollagen gene expression in silica-induced granulomatous lung disease and implication of transforming growth factor-beta as a mediator of fibrosis.

We have used the silica-induced model of pulmonary injury in the rat to study the pattern of collagen expression in granulomatous lung inflammation. A single intratracheal instillation of silica into adult rats resulted in granulomatous inflammation leading to fibrosis and alveolar proteinosis. The development of disease in these animals was characterized over a 27-day period after treatment by means of histological, biochemical, and molecular analyses. Biochemical analyses indicated that significant increases in the weights of silicotic lungs were due to elevated amounts of DNA and total protein. Analysis of hydroxyproline content showed a 15-fold increase in this amino acid in silicotic lungs, confirming the development of a fibrotic reaction. In situ hybridization for type I procollagen mRNA displayed increased gene expression in the parenchyma, conducting airways, and vasculature of silicotic rats. Within the parenchyma, type I procollagen was expressed uniquely within granulomatous lesions. Immunohistochemistry indicated type I procollagen was being expressed by an alpha-smooth muscle actin-negative population of cells. Immunolocalization of extra-cellular transforming growth factor-beta showed coincident temporal and spatial overlap with type I procollagen expression, implicating this cytokine as a mediator of collagen gene expression in this model.

Animals↗

PubMed1995

Increased elastin production in experimental granulomatous lung disease.

In the normal, healthy lung, elastin production is restricted to periods of development and growth. However, elastin expression in the adult lung has been observed in some forms of pulmonary injury, including pulmonary fibrosis. Here, we report that elastin production is significantly increased within precise interstitial compartments of the lung in an experimental model of granulomatous lung disease. An increase in the number and volume of elastic fibers within the alveolar walls was apparent on histological examination of Verhoeff-van Gieson-stained sections of silicotic rat lungs. Quantitation of mature elastin cross-links indicated that silicosis was accompanied by a 17-fold increase in lung elastin content when compared with values from saline-treated controls. In situ hybridization for tropoelastin mRNA revealed that elastin production was absent from granulomatous lesions yet was prominent at nonfibrotic alveolar septal tips, where a high density of elastic fibers is seen in the normal lung. Immunohistochemistry indicated tropoelastin was being expressed by alpha-smooth muscle actin-containing cells. Transforming growth factor-beta was immunolocalized to granulomatous regions of the silicotic lung but was absent from regions showing increased tropoelastin expression. These data indicate that the reinitiation of tropoelastin gene expression is associated with granulomatous lung disease, and this expression leads to the aberrant accumulation of mature elastin in the lung.

Actins↗

PubMed1994

Molecular structure of pulmonary surfactant protein D (SP-D).

Previous studies have shown that pulmonary surfactant protein D (SP-D) is composed of a 43-kDa polypeptide with a short NH2-terminal domain, a collagen sequence, and a COOH-terminal C-type lectin domain. In the present studies, ultrastructural and biochemical techniques were used to examine the quaternary structure of native rat SP-D (rSP-D). Electron microscopy of freeze-dried preparations demonstrated a highly homogeneous population of molecules with four identical rod-like arms (46 nm in length), each with an 8-9-nm diameter globular terminal expansion. The arms, which are similar in diameter to the type I collagen helix (approximately 4 nm), emanate from the central "hub" in two pairs that closely parallel each other for their first 10 nm. This structure is consistent with hydrodynamic studies that predict an highly asymmetric and extended molecule (f/f0 = 3.26) with a large Stokes radius (Rs = 18 nm). Pepsin digestion gave glycosylated, trimeric collagenous fragments (43 +/- 4 nm, 17 kDa/chain). Trimeric subunits containing intact triple helical domains were also liberated from SP-D dodecamers by sulfhydryl reduction under non-denaturing conditions. Digestion of rSP-D with bacterial collagenase generated a COOH-terminal carbohydrate binding fragment and a smaller peptide (approximately 12 kDa, unreduced) that contains interchain disulfide bonds. Electron microscopy also demonstrated higher orders of multimerization, with as many as 8 molecules associated at the hub. These studies demonstrate that SP-D is assembled as homopolymers of four identical trimeric subunits, that interactions between the amino-terminal domains of the trimers are stabilized by interchain disulfide bonds, and that SP-D molecules can associate to form complex multimolecular assemblies.

Amino Acid Sequence↗

PubMed1994

Recombinant pulmonary surfactant protein D. Post-translational modification and molecular assembly.

Pulmonary surfactant protein D (SP-D) is a member of a family of collagenous C-type lectins that includes the serum mannose binding proteins and surfactant protein A. Recent studies have shown that rat SP-D (rSP-D) molecules are assembled as tetramers of trimeric subunits (12 mers) and that dodecamers can participate in higher orders of molecular assembly involving interactions of the amino-terminal peptide domains. In order to further study the assembly of SP-D in vitro, Chinese hamster ovary K1 cells were transfected with a full-length rat SP-D cDNA, and stable transfectants with high levels of SP-D production (approximately 6 x 10(6) dodecamers/cell/24 h) were obtained using a glutamine synthetase selection system. The secreted molecules (RrSP-D), which were purified by affinity chromatography on maltosyl-agarose, comigrated with rSP-D on SDS-polyacrylamide gel electrophoresis in the presence and absence of reduction, and coeluted with rSP-D dodecamers from 4% agarose. The major bacterial collagenase-resistant peptide showed a decreased mobility on reduction consistent with the formation of intrachain disulfide bonds. A 17-kDa pepsin-resistant fragment was isolated following overnight digestion with pepsin at 27 degrees C, confirming the formation of a triple helical domain comparable in size and thermal stability to that of natural SP-D. The expressed protein contained sialylated endoglycosidase F-sensitive carbohydrate; amino acid analysis of acid and alkaline hydrolysates demonstrated essentially normal levels of hydroxyproline, hydroxylysine, and hydroxylysine-glycosides. Electron microscopic studies showed a molecular structure indistinguishable from lung SP-D, with a similar small subpopulation of molecules showing higher orders of multimerization. Solid-phase neoglycoprotein binding assays gave the same saccharide inhibition profile as natural rat SP-D, and both proteins showed efficient saccharide-dependent agglutination of Escherichia coli. These studies demonstrate that a single genetically distinct chain type can account for the various and complex molecular assemblies of SP-D, and further verify the potential physiologic significance of the disulfide-bonded multimers and higher aggregates isolated from rat, bovine, and human lung lavage.

Agglutination↗

PubMed1994

Modulation of surfactant protein D expression by glucocorticoids in fetal rat lung.

The production of pulmonary surfactant protein D (SP-D) increases abruptly during late gestation, and the accumulation of this protein in lung tissue is increased following the exposure of fetal rats to glucocorticoids in utero. To examine the regulation of these events, we administered dexamethasone (Dex; 1 mg/kg/day intramuscularly for 3 days), or saline, to timed-pregnant rats and harvested the lungs on days 19 to 21 of gestation. Samples of pooled fetal lungs were analyzed for SP-D protein, mRNA, and gene transcription by immunoblot, Northern hybridization, and nuclear run-off transcription assays. Lungs from 19 day controls showed barely detectable levels of SP-D gene transcription and negligible accumulation of SP-D message. However, SP-D transcription and the accumulation of SP-D mRNA and protein were readily detected in lungs from 19 day Dex-treated rats. Dexamethasone also caused dose- and time-dependent increases in SP-D protein and mRNA accumulation in 19 day fetal lung explants. Immunohistochemistry of control 19 day lung using antibodies to rat SP-D showed only weak labeling of a small number of airway epithelial cells. By contrast, Dex-exposed rats showed strong staining of columnar and cuboidal epithelial cells lining airways and epithelial tubules and cuboidal cells lining primitive air sacs. In situ hybridization assays showed similar alterations in the number, intensity, and distribution of labeled epithelial cells in 19 day Dex-exposed lungs and demonstrated labeling of alveolar type II and nonciliated columnar cells in adult lung. These data indicate that the accelerated lung maturation accompanying glucocorticoid exposure in utero is associated with a precocious increase in SP-D gene transcription and protein production by pulmonary epithelial cells.

Animals↗

PubMed1994

Lectin-mediated interactions of surfactant protein D with alveolar macrophages.

Surfactant protein D (SP-D) is a calcium-dependent carbohydrate-binding protein that is secreted into the pulmonary airspaces by type II epithelial and Clara cells. Previous studies have shown that SP-D can bind to specific surfactant phospholipids and to glycoconjugates associated with the surface of various microorganisms, consistent with possible roles in surfactant metabolism and pulmonary host defense. We now describe specific saccharide-mediated interactions of SP-D with alveolar macrophages in lung tissue and in vitro. Biotinylated rat SP-D showed specific binding to alveolar macrophages in sections of rat lung; this labeling was inhibited by competing saccharides or EDTA. In addition, the binding of 125I-SP-D to isolated alveolar macrophages in the presence of calcium was time-dependent, saturable, and reversible and was preferentially inhibited by known monosaccharide and disaccharide ligands for SP-D. Scatchard analysis gave an apparent single class of binding sites with a Kd = 1.4 x 10(-6) M. We speculate that the multivalent structure of SP-D mediates bridging interactions between microbial glycoconjugates or surfactant phospholipids and specific glycosylated ligands expressed on the surface of phagocytic cells.

Acetylglucosamine↗

PubMed1993

Genomic organization of human surfactant protein D (SP-D). SP-D is encoded on chromosome 10q22.2-23.1.

Surfactant protein D (SP-D) is a member of the family of mammalian C-type lectins. SP-D is secreted into the pulmonary airspaces by lung epithelial cells and is believed to contribute to the lung's defense against inhaled microorganisms. We have previously characterized cDNAs specific for human SP-D (hSP-D). We now describe the partial characterization of genomic clones for hSP-D and present evidence for an SP-D gene with coding sequences spanning > 11 kilobases on the long arm of chromosome 10. Genomic sequencing demonstrated that the signal peptide/amino-terminal domain, the carbohydrate recognition domain, and the linking sequence between the collagen domain, and carbohydrate recognition domain are each encoded by a single exon, as for surfactant protein A and the mannose-binding protein C. However, sequencing also demonstrated a unique intron-exon structure for the collagen domain which is encoded on five exons, including four tandem exons of 117 bp. The latter exons show marked conservation in the predicted distribution of hydrophilic amino acids, consistent with tandem replication of this collagen gene sequence during evolution. Segregation analysis of HindIII digests of genomic DNA using specific cDNA probes demonstrated selective hybridization of radiolabeled hSP-D cDNA to chromosome 10- and 10q-containing human/hamster somatic hybrids. The presence of SP-D gene sequences was confirmed by DNA amplification using oligomers specific for sequences within the collagen domain of the hSP-D gene. Fluorescence in situ hybridization of metaphase chromosomes using genomic probes gave selective labeling of 10q22.2-23.1. We speculate that SP-D is encoded at a locus on 10q that includes the genes for surfactant protein A.

Amino Acid Sequence↗

PubMed1993

Accumulation of surfactant protein D in human pulmonary alveolar proteinosis.

Surfactant protein D (SP-D) is a collagenous calcium-dependent carbohydrate-binding protein that is structurally related to the serum mannose-binding proteins and pulmonary surfactant protein A. SP-D was initially characterized as a biosynthetic product of freshly isolated rat type II cells and first purified in chemical amounts from bronchoalveolar lavage of rats with silica-induced alveolar lipoproteinosis. The present studies describe the characterization of human SP-D isolated from therapeutic bronchoalveolar lavage of patients with pulmonary alveolar proteinosis. Human proteinosis SP-D was extracted from the 10,000 x g pellet of bronchoalveolar lavage with 100 mmol/L glucose or ethylenediamine tetraacetic acid, and specifically bound to and eluted from maltosyl-agarose. The protein cross-reacted with monospecific antibodies to rat SP-D by enzyme-linked immunosorbent assay and immunoblot and eluted near the position of rat SP-D on reverse-phase high performance liquid chromatography. When chromatographed on 4% agarose (A-15M) in the presence of ethylenediamine tetraacetic acid, the solubilized human proteinosis SP-D eluted near the void volume and earlier than rat SP-D dodecamers or human SP-D multimers in the lavage supernatant. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of proteins in the lavage pellet with antibodies to the carbohydrate-binding domain of proteinosis human SP-D demonstrated covalently cross-linked multimers of SP-D monomers (43 kd, reduced) and multimers of trimeric components stabilized by disulfide and non-disulfide bonds. These studies describe the isolation and biochemical characterization of human SP-D and demonstrate the abnormal accumulation of this protein in the air spaces of patients with alveolar proteinosis.

Amino Acid Sequence↗

PubMed1992

Velocity of mammalian skeletal muscle contraction as a function of fiber type, activation, initial length and temperature.

Multiple stepwise regression analyses techniques were applied to develop modifications of the Hill force-velocity equation. Specifically, predictive models of the Hill a coefficient, the Hill b coefficient, and isometric strength P0 were developed for the following set of variables: the fraction of slow-twitch fibers (X), the recruitment magnitude (A), the initial muscle length (L), and the muscle temperature (T). Results indicate that the Hill a and Hill b coefficients and isometric strength P0 can be predicted with a high degree of accuracy. The utility of the equation is that it would allow development of a computer program to control the velocity of contraction of muscles with differing fiber compositions and lengths such as are found in the leg.

Animals↗

PubMed1992

Surfactant protein D: subcellular localization in nonciliated bronchiolar epithelial cells.

Surfactant protein D (SP-D, CP4) is a collagenous surfactant-associated carbohydrate binding protein that was initially characterized as a biosynthetic product of type II pneumocytes. Immunoperoxidase studies of formaldehyde solution-fixed and paraffin-embedded rat lung demonstrated staining for SP-D in the cytoplasm of a subpopulation of bronchiolar epithelial cells as well as type II cells. Accordingly, immunogold-labeling techniques were used to further examine the cellular distribution and subcellular localization of SP-D in the small airways. Lung tissues were fixed with 0.5% glutaraldehyde-3% paraformaldehyde and embedded in LR White resin. Sections were reacted with affinity purified polyclonal antibodies to SP-D, and sites of antibody binding were demonstrated using a biotinylated secondary antibody-streptavidin-gold detection system. Anti-SP-D selectively decorated secretory compartments of nonciliated bronchiolar cells (Clara cells) with strong and specific labeling of apical electron-dense secretory granules. Almost all of the granules in nonciliated columnar cells were labeled; however, labeling was typically nonuniform, with preferential decoration of the periphery of the granule. The largest numbers of immunoreactive epithelial cells were observed in the distal membranous bronchioles, with progressively smaller numbers of cells in more proximal bronchioles. There was no detectable labeling of cells lining the large cartilagenous airways or trachea. These studies provide evidence that SP-D is a secretory product of nonciliated bronchiolar cells. We suggest that Clara cell-derived SP-D is a component of bronchiolar lining material, consistent with our hypothesis that SP-D contributes to surfactant metabolism and/or host defense within small airways.

Animals↗

PubMed1992

Interactions of surfactant protein D with bacterial lipopolysaccharides. Surfactant protein D is an Escherichia coli-binding protein in bronchoalveolar lavage.

Surfactant protein D (SP-D) is a collagenous glycoprotein that is secreted into the pulmonary airspaces by alveolar type II and nonciliated bronchiolar cells. SP-D exhibits Ca(++)-dependent carbohydrate binding in vitro and is structurally related to the collagenous C-type lectins, including serum conglutinin, serum mannose-binding proteins, and surfactant protein A. Preliminary studies showed calcium- and saccharide-dependent binding of fluorescein-conjugated or radioiodinated SP-D to a variety of microorganisms, including Gram-negative bacteria and fungi. A laboratory strain of Escherichia coli (Y1088) was chosen to further examine the mechanism(s) of binding. Binding of SP-D to Y1088 was time dependent, saturable, and inhibited by cold SP-D or competing saccharides; Scatchard analysis gave a Kd of 2 x 10(-11) M. At higher concentrations, SP-D also caused Ca(++)-dependent agglutination of Y1088 that was inhibited by alpha-glucosyl-containing saccharides, antisera to the carbohydrate-binding domain of SP-D, or Y1088 LPS. Lectin blots showed specific binding of 125I-SP-D to Y1088 LPS, as well as LPS from other several strains of enteric Gram-negative bacteria. Immunogold studies demonstrated strong and uniform surface labeling of the bacteria. Rat and human bronchoalveolar lavage (BAL) caused Ca(++)-dependent agglutination of E. coli that was dose dependent and inhibited by competing saccharides or anti-SP-D. SP-D was selectively and efficiently adsorbed from rat BAL by incubation with E. coli, and incubation of E. coli with radiolabeled rat type II cell medium revealed that SP-D is the major E. coli-binding protein secreted by freshly isolated cells in culture. We suggest that SP-D plays important roles in the lung's defense against Gram-negative bacteria.

Agglutination↗

PubMed1992

Curettage and cautery of skin conditions.

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Basal Cell Carcinoma↗

PubMed1991

Human surfactant protein D: SP-D contains a C-type lectin carbohydrate recognition domain.

Lung surfactant protein D (SP-D) shows calcium-dependent binding to specific saccharides, and is similar in domain structure to certain members of the calcium-dependent (C-type) lectin family. Using a degenerate oligomeric probe corresponding to a conserved peptide sequence derived from the amino-terminus of the putative carbohydrate binding domain of rat and bovine SP-D, we screened a human lung cDNA library and isolated a 1.4-kb cDNA for the human protein. The relationship of the cDNA to SP-D was established by several techniques including amino-terminal microsequencing of SP-D-derived peptides, and immunoprecipitation of translation products of transcribed mRNA with monospecific antibodies to SP-D. In addition, antibodies to a synthetic peptide derived from a predicted unique epitope within the carbohydrate recognition domain of SP-D specifically reacted with SP-D. DNA sequencing demonstrated a noncollagenous carboxy-terminal domain that is highly homologous with the carboxy-terminal globular domain of previously described C-type lectins. This domain contains all of the so-called "invariant residues," including four conserved cysteine residues, and shows high homology with the mannose-binding subfamily of C-type lectins. Sequencing also demonstrated an amino-terminal collagenous domain that contains an uninterrupted sequence of 59 Gly-X-Y triplets and that also contains the only identified consensus for asparagine-linked oligosaccharides. The studies demonstrate that SP-D is a member of the C-type lectin family, and confirm predicted structural similarities to conglutinin, SP-D, and the serum mannose binding proteins.

Amino Acid Sequence↗

PubMed1991

Primary translation products of pulmonary surfactant protein D.

Surfactant protein D (SP-D) is a collagenous, surfactant-associated, carbohydrate-binding protein that is synthesized by alveolar type II epithelial cells. To further characterize SP-D, we isolated RNA from adult rat lungs and rat type II cells and translated mRNAs in vitro. [35S]methionine-labeled translation products were precipitated with antibodies to rat SP-D, resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and visualized by fluorography. Immune precipitates of translation reactions for rat lung or rat type II cells demonstrated a single collagenous polypeptide (39.3 kDa) that was smaller than surfactant-associated SP-D (43 kDa, reduced) but larger than the mature secreted form of rat SP-A. This component was not identified in translation reactions of rat liver, gut, brain, mammary gland, or rat L2 cell RNA. There was a fivefold enrichment of SP-D mRNA in freshly isolated type II cells relative to lung; however, the levels of translatable SP-D mRNA decreased rapidly during the first 24 h of cell culture. The SP-D translation product migrated faster than the major cellular form of SP-D but approximately 1 kDa slower than cellular SP-D synthesized in the presence of 2,2'-dipyridyl plus tunicamycin. Translation in the presence of canine pancreatic microsomes gave a single glycosylated, endoglycosidase F-sensitive form (40.6 kDa) and demonstrated cleavage of a small signal peptide. These results indicate that SP-D is a secretory product of differentiated type II epithelial cells and that SP-D is secreted in a mature form that does not undergo further proteolytic processing in vivo.

Animals↗

PubMed1991

Developmental expression of pulmonary surfactant protein D (SP-D).

Surfactant protein D (SP-D) is a collagenous, surfactant-associated, carbohydrate-binding protein that is synthesized by pulmonary epithelial cells. In the present studies, we examined the expression of SP-D and SP-D mRNA during late fetal (day 17, 19, 21) and early postnatal (day 5) rat lung development using immunochemical, cell-free translation, and Northern hybridization assays. SP-D mRNA and immunoreactive SP-D protein were first detected in guanidine extracts of whole rat lung at 21 days of gestation and reached even higher concentrations during the postnatal period. Likewise, immunoperoxidase studies of rat lung using affinity-purified antibodies to SP-D showed no staining at day 17 or 19, but demonstrated strong cytoplasmic staining of cuboidal epithelial cells lining immature airspaces at day 21 and strong cytoplasmic staining of type II and nonciliated bronchiolar cells in adult lung. SP-D also appeared in amniotic fluid by day 21 and was partially purified by affinity chromatography on maltosyl-agarose under conditions used for the isolation of rat lung SP-D. These studies indicate that the production of SP-D is increased shortly prior to birth, and that the increases in total lung SP-D and SP-D mRNA are temporally correlated with SP-D secretion and the appearance of SP-D in amniotic fluid.

Amino Acid Sequence↗