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Biomedical subjects

K B Reid

Publications and source records attributed to K B Reid.

At least 73 records · Page 4Linked to original sources
PubMed1996

Human C1q induces eosinophil migration.

Eosinophils (Eo) play a significant role in allergic inflammation and the host's immunity to parasitic infections. Although the presence of C1q-binding cell surface molecule(s) (C1q-R) on Eo had been previously implicated by the ability of C1q to augment IgG-dependent, Eo-mediated killing of schistosomula, little is known about the structure or the function of this receptor. The present studies were therefore undertaken to immunochemically demonstrate and to examine the biology of Eo C1q-R. Eo were purified to homogeneity (>90%) and viability (>98%) from hypereosinophilic donors by Percoll density gradient. Western blot analysis using antibodies to cC1q-R and gC1q-R showed distinct bands corresponding to cC1q-R (60 kDa) and gC1q-R (33 kDa) when immunoblotted with their respective antibodies. The Eo C1q-R was tested for its ability to induce chemokinesis and/or chemotaxis as assessed by the modified Boyden microchamber assay utilizing 5-micrometer-pore polycarbonate membranes and using C1q, cC1q, or gC1q (10 micrograms/ml) as agonists. The known chemotactic factors C5a and RANTES (10(-8)M) were used as positive controls. The results showed that at this concentration, cC1q was most efficient in its ability to induce Eo migration (20 +/- SEM 12, n = 4) followed by C1q (107 +/- SEM 7, n=7) and gC1q (77 +/- SEM 10, n = 10). When checkerboard analysis was performed, the data indicated that the observed phenomenon was likely to be due largely to chemokinesis. As expected, C5a (145 +/- SEM 15, n = 7) and RANTES (145 +/- SEM 43, n = 7) were both chemotactic. Furthermore, incubation of Eo with 50 micrograms of either C1q, gC1q, or cC1q (1 hr, 37 degrees C) did not cause release of eosinophil cationic protein as measured by RIA, nor did it enhance the expression of CD11b or CD29 as assessed by FACS analysis. The data presented in this paper show that Eo express both cC1q-R and gC1q-R and may participate in Eo function by providing a primary signal for locomotion.

Blood Proteins↗
PubMed1996

Interaction of human lung surfactant proteins A and D with mite (Dermatophagoides pteronyssinus) allergens.

Human lung surfactant proteins A (SP-A) and D (SP-D) are both collagenous C-type lectins which appear to mediate antimicrobial activity by binding to carbohydrates on micro-organisms and to receptors on phagocytic cells. Purified native SP-A and SP-D, isolated from human bronchoalveolar lavage fluid, were found to bind to whole mite extracts (Dermatophagoides pteronyssinus) and the purified allergen Der p I, in a carbohydrate-specific and calcium-dependent manner. Binding was inhibited by ethylenediamine tetra-acetic acid (EDTA) as well as by maltose in the case of SP-D, or mannose in the case of SP-A. A recombinant polypeptide, which trimerized to form the neck region and carbohydrate recognition domains of SP-D, also inhibited the binding of native SP-D to the whole mite extract and Der p I. Both SP-A and SP-D did not bind to deglycosylated whole mite extracts or to recombinant Der p proteins, which lacked carbohydrate residues. These results suggest that the ability of surfactant proteins to bind certain allergens is mediated through their carbohydrate-recognition domains (CRDs) interacting with carbohydrate residues on the allergens. Moreover, SP-A and SP-D were found to inhibit allergen-specific IgE binding to the mite extracts either via steric hindrance or competitive binding. It is therefore possible that SP-A and SP-D may be involved in the modulation of allergen sensitization and/or the development of allergic reactions.

Allergens↗
PubMed1996

Identification of functional domains on gC1Q-R, a cell surface protein that binds to the globular "heads" of C1Q, using monoclonal antibodies and synthetic peptides.

A membrane protein (33 kDa) that binds to the globular "heads" of C1q (gC1q-R) has been recently described. The full length cDNA encoding gC1q-R has been cloned, expressed in E. coli and using the purified recombinant protein (rgC1q-R) as an immunogen, a panel of IgG monoclonal antibodies (MAb) has been produced by fusion of spleen cells from hyperimmunized BALB/c mice with NSO mouse myeloma partners. From this fusion, 60 anti-gC1q-R hybridomas were selected and evaluated for their ability to (1) discriminate between the mature form (MF) of gC1q-R (residues 74-282) and a truncated form (TF) lacking residues 74-95, which contains a major C1q binding site, (2) recognize two functionally defined synthetic peptides derived from the NH2-(XN18) and COOH-(XC15) terminus of gC1q-R, and (3) bind to microtiter well fixed intact Raji cells. Several clones were identified: MAbs 46.23 and 60.11 (IgG1 kappa), reacted strongly with ELISA plate-fixed intact Raji and K562 cells, MF, and the XN18 peptide, but had poor or no reactivity with TF; MAbs 74.5.2 > 25.15 (IgG1 kappa) recognized both MF and TF and are directed against epitopes in the XC15 peptide that contains a binding site for high-molecular-weight kininogen and Factor XII.

Amino Acid Sequence↗
PubMed1996

Measurement of pulmonary status and surfactant protein levels during dexamethasone treatment of neonatal respiratory distress syndrome.

BACKGROUND: Early postnatal use of dexamethasone in infants with respiratory distress syndrome (RDS) has been shown effectively to improve pulmonary status and to allow early weaning off mechanical ventilation. However, the mechanisms to explain the beneficial effects of dexamethasone in ventilatory dependent preterm infants remain unclear. METHODS: A double blind, placebo controlled study was performed to determine the change in pulmonary ventilation of premature infants with RDS as a result of dexamethasone treatment, and to evaluate the effect of dexamethasone on the levels of surfactant-associated proteins A (SP-A) and D (SP-D) in the tracheal fluid from 34 premature infants with RDS and 29 control subjects. RESULTS: Dexamethasone treatment decreased fractional inspired oxygen concentration (FIO2), arterial carbon dioxide tension (PCO2), mean airway pressure (MAP), and facilitated successful weaning from mechanical ventilation. SP-A concentrations in the tracheal aspirates were increased at days 7 and 14, and SP-D concentrations were increased during the period from days 3 to 14 in the dexamethasone treated group compared with the control group. However, albumin levels in the tracheal aspirate samples were decreased after dexamethasone treatment over the period from days 3 to 14. There was an inverse correlation between PCO2 values and SP-A concentrations. CONCLUSIONS: These results suggest that early use of dexamethasone can improve pulmonary status and also increase SP-A and SP-D levels in the tracheal fluid in premature infants with RDS.

Albumins↗
PubMed1995

Characterization of mutant forms of recombinant human properdin lacking single thrombospondin type I repeats. Identification of modules important for function.

Properdin is a serum glycoprotein that up-regulates the alternative pathway of complement by stabilizing the C3b-Bb complex. It also binds sulfated glycoconjugates, such as sulfatide, in vitro. Properdin is composed of cyclic dimers, trimers, and tetramers of a 53-kDa monomeric subunit. The monomer contains an N-terminal region of no known homology and six thrombospondin type 1 repeats (TSRs) of approximately 60 amino acids. To identify the regions of properdin important for function, we have expressed human properdin, and mutant forms each lacking a single TSR, in Chinese hamster ovary cells. In addition, limited tryptic digestion yielded "nicked" properdin by the cleavage of one peptide bond in TSR5. The structural and functional properties of these altered forms of properdin were investigated. Properdin "nicked" in TSR5 is unable to bind C3b but retains its overall structure and its ability to bind sulfatide. The removal of TSR5 prevents C3b and sulfatide binding. Properdin lacking TSR4 is unable to stabilize the C3b-Bb complex but is able to bind C3b and sulfatide, and shows the presence of monomers and dimers in an electron microscope. Properdin without TSR3 is able to stabilize the C3b-Bb complex, to bind C3b and sulfatide, and forms dimers, trimers, and tetramers. Properdin lacking TSR6 is unable to form oligomers. The N-linked carbohydrate of properdin is not required for oligomerization or stabilization of the C3b-Bb complex. The results implicate TSR5 in both C3b and sulfatide binding, and suggest that TSR4 may also be involved in stabilization of the C3b-Bb complex.

Amino Acid Sequence↗
PubMed1995

A recombinant polypeptide, composed of the alpha-helical neck region and the carbohydrate recognition domain of conglutinin, self-associates to give a functionally intact homotrimer.

A recombinant polypeptide composed of the alpha-helical neck region and carbohydrate recognition domain (CRD) of bovine conglutinin was expressed in Escherichia coli. The recombinant protein formed inclusion bodies but could be solubilised using a denaturation-renaturation cycle based on urea and then purified by affinity chromatography on a TSK-N-acetylglucosamide column. The purified product behaved as a homotrimer in non-dissociating conditions, with three CRDs held together by the alpha-helical neck regions. The trimer, although lacking the N-terminal and collagen regions of the native conglutinin, showed the same binding carbohydrate specificities as the native molecule, for the complement fragment C3b and for lipopolysaccharides derived from Gram-negative bacteria.

Animals↗
PubMed1995

Murine mast cells express two types of C1q receptors that are involved in the induction of chemotaxis and chemokinesis.

Although previous studies have shown that different cells and cell lines of murine origin bind human C1q, suggesting that they display cell surface receptors for C1q, no information is available to indicate whether mouse or human mast cells express C1q receptors. This paper presents the first evidence to show that murine mast cells express specific receptors for C1q. Western blot analysis of cell membrane proteins prepared from a bone marrow-derived mouse cell line using two monospecific polyclonal Abs, one directed against the 60-kDa C1q receptor (C1q-R) that binds to the collagen-like stalk of C1q (cC1q-R) and the other directed against the 33-kDa molecule that binds to the globular "heads" of C1q (gC1q-R), show that both of these receptors are present on these cells. In addition, C1q can induce mast cell migration in a specific and dose-dependent manner. Interestingly, the C1q-induced migratory response was found to be biphasic; the first response peaked at a C1q concentration of 0.1 nM, whereas the second phase peaked at approximately 40 nM. Checkerboard analysis of the mast cell migratory response to C1q showed that the first phase was primarily due to chemotaxis and the second phase was attributable to chemokinesis. Preincubation of C1q with Abs specific for the collagen-like tail of the molecule abolished both its chemotactic and chemokinetic response, whereas heat inactivation of C1q (56 degrees C, 1 h) resulted in 85% abrogation of the chemotactic phase and 42% reduction in the chemokinetic phase. The observed mast cell migratory responses were mediated by cell surface C1q-R(s), as inclusion of a mixture of anti-C1q-R and anti-gC1q-R Abs with the cells inhibited their migratory response toward C1q. However, incubation of cells with various doses of C1q did not result in histamine release. Furthermore, engagement of mast cell C1q-Rs by the ligand C1q induced an antiproliferative response, as coculturing of mast cells with C1q resulted in a specific and dose-dependent decrease in DNA synthesis. These data suggest that C1q-Rs may play a significant role in mast cell function and regulation by providing an important signal through which mast cells can be recruited to inflammatory sites of increased C1q concentration.

Animals↗
PubMed1995

Comparative study of the structural and functional properties of a bovine plasma C-type lectin, collectin-43, with other collectins.

Collectin-43 (CL-43) is a recently described bovine plasma protein containing both collagenous regions and C-type-lectin domains [Holmskov, Teisner, Willis, Reid and Jensenius (1993) J. Biol. Chem. 268, 10120-10125; Lim, Willis, Reid, Lu, Laursen, Jensenius and Holmskov (1994) J. Biol. Chem. 269, 11820-11824]. CL-43 was purified by affinity chromatography on mannan-Sepharose. On SDS/PAGE under reducing conditions the purified lectin showed a double band at about 43 kDa, with the upper band representing the intact molecule and the lower band a truncated form that lacked the N-terminal nine amino acid residues. Under non-reducing conditions, only one band was seen at 120 kDa. Analytical gel chromatography and sucrose-density-gradient centrifugation of the purified molecule, showed a Stokes radius of 9.1 +/- 0.3 nm (91 +/- 3 A) and a sedimentation coefficient (s20,w) of 3.6 +/- 0.1 S. These values correspond to a molecular mass of 119-138 kDa under non-denaturing condition in solution. The frictional coefficient (f/f0) was 2.7, indicating extreme elongation due to the collagenous segment. Only monomer subunits, with 37.4 +/- 1.7-nm-long rods, were seen by electron microscopy. These findings indicate that CL-43, in contrast with the other circulating collectins, is found only as a single subunit composed of three polypeptide chains. Two-dimensional gel electrophoresis showed that CL-43 has two isoforms, with pI values of 4.9 and 5.3, corresponding to the native form and the truncated form of the molecule respectively. CL-43, like conglutinin, lung surfactant protein A and mannan-binding protein (MBP), was shown to bind to the collectin receptor. Bovine MBP caused the activation of the complement system as revealed by the deposition of complement component C4 upon incubation of diluted serum in wells containing MBP bound to solid-phase mannan. CL-43, lung surfactant protein D (SP-D) and conglutinin showed no complement-activating properties under the same conditions. Conglutinin binds fluid- and solid-phase iC3b, while CL-43 and MBP do not show such reactivity.

Animals↗
PubMed1995

Circulating levels of mannose binding protein in human immunodeficiency virus infection.

Mannose binding protein (MBP) is a serum lectin which, upon binding to a carbohydrate extremity, acquires the ability to activate the classical complement pathway. MBP binds human immunodeficiency virus (HIV) in vitro via glycans on gp120 and thus, it may play a defensive role in HIV infection and contribute to virus clearance through the activation of complement associated with this condition. We measured serum MBP and activation indices of the classical complement pathway (plasma C4d and C3d) in HIV-seropositive patients at different stages of disease severity, and in normal subjects. MBP was higher in HIV patients as a whole and in each Centers for Disease Control (CDC) group than controls (P<0.01). MBP was not significantly different between CDC groups and and did not significantly correlate either with CD4-positive lymphocytes, neopterin or beta2-microglobulin or with C4d and C3d. The possibility that MBP plays a defensive role in HIV infection cannot be excluded, but, it it is, it does not appear to act by recruiting complement for vital elimination.

Adult↗
PubMed1995

Identification of a gC1q-binding protein (gC1q-R) on the surface of human neutrophils. Subcellular localization and binding properties in comparison with the cC1q-R.

Human neutrophils have multiple C1q-binding proteins. Direct ligand-binding studies with the globular domain of C1q and two-dimensional Western blot analysis revealed two gC1q-binding proteins (gC1q-R): a 33,000 M(r) protein (pI 4.5) mainly in the neutrophil plasma membrane and an 80,000-90,000 M(r) protein (pI 4.1-4.2) located mainly in the granules. Direct binding studies showed that C1q bound to this higher molecular weight protein under physiological conditions. In contrast, anti-cC1q-R antibody, which recognizes a protein binding to collagenous tails of C1q, detected only a 68,000 M(r) protein in the plasma membrane. Both the 33,000 and 68,000 M(r) receptors appear early on the surface of differentiating HL-60 cells. On mature neutrophils, surface expression of both C1q receptors was evident, but no upregulation was observed upon stimulation. Phorbol myristate acetate treatment of neutrophils downregulated both the receptors from cell surface, and significant amounts of soluble gC1q-R were in cell media supernatants, suggesting receptor shedding or secretion. gC1q-R, unlike cC1q-R, did not bind to other C1q-like ligands, namely mannose binding protein, surfactant protein-A, surfactant protein-D, or conglutinin under normal ionic conditions, suggesting a greater specificity for C1q than the "collectin" type receptor (cC1q-R). Rather, gC1q-R only bound purified C1q, and the binding was enhanced under low ionic conditions and in the absence of calcium. The role of C1q receptor shedding and its biologic consequence remain to be defined, but may contribute to the diversity of C1q-mediated responses observed in many cell types.

Blotting, Western↗
PubMed1994

Trimeric C-type lectin domains in host defence.

Recent crystal structures, established for fragments of human and rat mannose-binding proteins, indicate that the triple-stranded alpha-helical coiled coil present in these collectins is responsible for the trimeric orientation of C-type lectin domains.

Amino Acid Sequence↗
PubMed1994

Expression of the carbohydrate recognition domain of lung surfactant protein D and demonstration of its binding to lipopolysaccharides of gram-negative bacteria.

Surfactant protein D is a collagenous C-type lectin (collectin) that is found almost exclusively in the lung. A recombinant protein, composed of the neck-region and the carbohydrate binding domain of bovine lung surfactant protein D, has been overexpressed in E. coli. The recombinant protein showed the same sugar binding specificity as the native protein and was able to bind to the lipopolysaccharides of several strains of Gram-negative bacteria, such as Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli, which are known to cause lung infections. The binding was calcium-dependent and was inhibited by maltose. Native bovine surfactant protein D was also shown to be able to bind to these lipopolysaccharides in the same manner.

Animals↗
PubMed1994

Beta-sheet secondary structure of the trimeric globular domain of C1q of complement and collagen types VIII and X by Fourier-transform infrared spectroscopy and averaged structure predictions.

C1q plays a key role in the recognition of immune complexes, thereby initiating the classical pathway of complement activation. Although the triple-helix conformation of its N-terminal segment is well established, the secondary structure of the trimeric globular C-terminal domain is as yet unknown. The secondary structures of human C1q and C1q stalks and pepsin-extracted human collagen types I, III and IV (with no significant non-collagen-like structure) were studied by Fourier-transform i.r. spectroscopy in 2H2O buffers. After second-derivative calculation to resolve the fine structure of the broad amide I band, the Fourier-transform i.r. spectrum of C1q showed two major bands, one at 1637 cm-1, which is a characteristic frequency for beta-sheets, and one at 1661 cm-1. Both major bands were also detected for Clq in H2O buffers. Only the second major band was observed at 1655 cm-1 in pepsin-digested C1q which contains primarily the N-terminal triple-helix region. The Fourier-transform i.r. spectra of collagen in 2H2O also showed a major band at 1659 cm-1 (and minor bands at 1632 cm-1 and 1682 cm-1). It is concluded that the C1q globular heads contain primarily beta-sheet structure. The C-terminal domains of C1q show approximately 25% sequence identity with the non-collagen-like C-terminal regions of the short-chain collagen types VIII and X. To complement the Fourier-transform-i.r. spectroscopic data, averaged Robson and Chou-Fasman structure predictions on 15 similar sequences for the globular domains of C1q and collagen types VIII and X were performed. These showed a clear pattern of ten beta-strands interspersed by beta-turns and /or loops. Residues thought to be important for C1q-immune complex interactions with IgG and IgM were predicted to be at a surface-exposed loop. Sequence insertions and deletions, glycosylation sites, the free cysteine residue and RGD recognition sequences were also predicted to be at surface-exposed positions.

Amino Acid Sequence↗
PubMed1994

Identification of a novel 33-kDa C1q-binding site on human blood platelets.

The constitutive expression of a 60-kDa platelet membrane protein (cC1qR) recognizing the collagen-like amino terminal of C1q was previously described. Recently, a novel 33-kDa C1q receptor (gC1qR) that interacts with the globular head region of C1q was identified on Raji cells, as well as PBLs, neutrophils, and eosinophils. The present study demonstrates that polyclonal Abs directed against this novel C1q-binding protein also recognize a 33-kDa platelet membrane constituent on Western blots. Interestingly, Ab reactivity with platelets in suspension was minimal, but increased nearly 10-fold after platelet adhesion to collagen, fibrinogen, or fibronectin-coated surfaces. Similar increases in Ab reactivity were not achieved after platelet stimulation in suspension, even with strong agonists such as thrombin or A23187. Platelet function studies, however, demonstrated that both the globular C-terminal domain of C1q and the collagen-like N-terminal region participate in platelet aggregation in response to C1q multimers. Moreover, a synthetic 18 amino acid peptide (X18) corresponding to the amino terminal sequence of the cloned Raji cell gC1qR inhibited both platelet adhesion to immobilized C1q and aggregated C1q-induced platelet aggregation. Aggregated C1q-induced platelet aggregation was also inhibited by a mAb (1B4) directed against the recombinant gC1qR. The data support the involvement of both carboxy- and amino-terminal regions of C1q in platelet-C1q interactions, and suggest a role for the gC1qR in this process.

Binding Sites↗
PubMed1994

Isolation, cDNA cloning, and overexpression of a 33-kD cell surface glycoprotein that binds to the globular "heads" of C1q.

This work describes the functional characterization, cDNA cloning, and expression of a novel cell surface protein. This protein designated gC1q-R, was first isolated from Raji cells and was found to bind to the globular "heads" of C1q molecules, at physiological ionic strength, and also to inhibit complement-mediated lysis of sheep erythrocytes by human serum. The NH2-terminal amino acid sequence of the first 24 residues of the C1q-binding protein was determined and this information allowed the synthesis of two degenerate polymerase chain reaction primers for use in the preparation of a probe in the screening of a B cell cDNA library. The cDNA isolated, using this probe, was found to encode a pre-pro protein of 282 residues. The NH2 terminus of the protein isolated from Raji cells started at residue 74 of the predicted pre-pro sequence. The cDNA sequence shows that the purified protein has three potential N-glycosylation residues and is a highly charged, acidic molecule. Hence, its binding to C1q may be primarily but not exclusively due to ionic interactions. The "mature" protein, corresponding to amino acid residues 74-282 of the predicted pre-pro sequence, was overexpressed in Escherichia coli and was purified to homogeneity. This recombinant protein was also able to inhibit the complement-mediated lysis of sheep erythrocytes by human serum and was shown to be a tetramer by gel filtration in nondissociating conditions. Northern blot and RT-PCR studies showed that the C1q-binding protein is expressed at high levels in Raji and Daudi cell lines, at moderate levels in U937, Molt-4, and HepG2 cell lines, and at a very low level in the HL60 cell line. However, it is not expressed in the K562 cell line. Comparison of gC1q-R NH2-terminal sequence with that of the receptor for the collagen-like domain of C1q (cC1q-R) showed no similarity. Furthermore, antibodies to gC1q-R or an 18-amino acid residue-long NH2-terminal synthetic gC1q-R peptide did not cross-react with antibodies to cC1q-R. Anti-gC1q-R immunoblotted a 33-kD Raji cell membrane protein, whereas anti cC1q-R recognized a molecule of approximately 60 kD. The NH2-terminal sequence of gC1g-R appears to be displayed extracellularly since anti-gC1g-R peptide reacted with surface molecules on lymphocytes, polymorphonuclear leukocytes, and platelets, as assessed by flow cytometric and confocal laser scanning microscopic analyses.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1994

A parallel three stranded alpha-helical bundle at the nucleation site of collagen triple-helix formation.

A short stretch of 35 amino acids is identified as the structural motif responsible for the tight parallel association and trimerization of the three identical polypeptide chains of lung surfactant protein D, which contains both collagen regions and C-type lectin domains. This 'neck-region' is located at the nucleation site at which the collagenous sequences fold into a staggered triple-helix and is shown, by CD, NMR, and cross-linking of recombinant peptides, to consist of a triple-stranded parallel alpha-helical bundle in a non-staggered, and extremely strong, non-covalent association. This type of association between three polypeptide chains may represent a common structural feature immediately following the C-terminal end of the triple-helical region of collagenous proteins.

Amino Acid Sequence↗
PubMed1994

Surfactant protein D binding to alveolar macrophages.

Surfactant protein D (SP-D) is a lung-specific protein, synthesized and secreted by lung epithelial cells. It belongs to group III of the family of C-type lectins; each member of this group has an unusual overall structure consisting of multiple globular 'head' regions (which contain the C-type lectin domains) linked by triple-helical, collagen-like, strands. This group includes the surfactant protein A (SP-A) and the serum proteins mannan-binding protein, conglutinin and collectin-43, all of which have been shown to bind to the C1q receptor found on a wide variety of cells, including macrophages. Both SP-D and SP-A have been shown to enhance oxygen radical production by alveolar macrophages. Although this strongly suggests a direct interaction between SP-D and a specific receptor on alveolar macrophages, it is still unclear whether SP-D binds to the same receptor used by SP-A and/or C1q. Human SP-D was isolated from amniotic fluid and was radiolabelled using 125I. Alveolar macrophages were isolated from human bronchioalveolar lavage fluid, and also from bovine lung washings, by differential adhesion to 24-well tissue-culture plates. The study was carried out using EDTA-containing buffers, to eliminate Ca(2+)-dependent C-type lectin binding, and was also carried out at 4 degrees C to eliminate possible internalization by the cells. 125I-SP-D showed specific binding to alveolar macrophages in both a time- and concentration-saturable manner. The binding was inhibited, by approx. 90%, on addition of a 200-fold excess of unlabelled SP-D. The apparent dissociation constant (Kd) was (3.6 +/- 1.3) x 10(-11) M, based on the assumption that native SP-D is assembled as a dodecamer of 12 identical polypeptides of 43 kDa to yield a protein of 516 kDa. C1q was also shown to bind alveolar macrophages (Kd 3 x 10(-6) M), but addition of C1q did not show inhibition of the binding of 125I-SP-D to the macrophages. We conclude that SP-D binds specifically to alveolar macrophages and the receptor involved is different from that utilized by C1q.

Animals↗