In vivo morphometric analysis of inflammatory condylar changes in rat temporomandibular joint.

OBJECTIVE: Injection of complete Freund's adjuvant (CFA) into the temporomandibular joint (TMJ) causes acute swelling around the joint and subsequent morphological alterations in the condyle. We aimed to evaluate changes in the three-dimensional architecture of the condyle induced with CFA. MATERIALS AND METHODS: The CFA was injected into the unilateral TMJ of rats and morphological changes in the condyle were assessed repeatedly for 14 days by in vivo micro-CT. RESULTS: Osseous abnormalities of condyle were first observed at 3-5 days after CFA injection on the tomographic images, and the condylar deformation became more obvious thereafter. Among 12 condyles examined at 14 days postinjection, osteophytosis was observed in all of the specimens and bone erosion coexisted in five condyles. None of the saline-treated condyles showed architectural changes. Significant changes were detected in the mesiolateral and rostrocaudal widths of the CFA-treated condyles at 10-14 days postinjection (P < 0.01). The extent of both condylar bone formation and resorption was greater in the CFA-injected TMJs than in saline-injected TMJs (P < 0.05). CONCLUSION: These results indicate that CFA causes dynamic morphological changes in the condyle and that our experimental approach will provide new insights into the subacute inflammatory processes in the TMJ.

Site-directed mutagenesis of surfactant protein A reveals dissociation of lipid aggregation and lipid uptake by alveolar type II cells.

Surfactant protein A (SP-A) binds to dipalmitoylphosphatidylcholine (DPPC) and induces phospholipid vesicle aggregation. It also regulates the uptake and secretion of surfactant lipids by alveolar type II cells. We introduced the single mutations Glu195-->Gln (rE195Q), Lys201-->Ala (rK201A) and Lys203-->Ala (rK203A) for rat SP-A, Arg199-->Ala (hR199A) and Lys201-->Ala (hK201A) for human SP-A, and the triple mutations Arg197, Lys201 and Lys203-->Ala (rR197A/K201A/K203A) for rat SP-A, into cDNAs for SP-A, and expressed the recombinant proteins using baculovirus vectors. All recombinant proteins avidly bound to DPPC liposomes. rE195Q, rK201A, rK203A, hR199A and hK201A function with activity comparable to wild type SP-A. Although rR197A/K201A/K203A was a potent inducer of phospholipid vesicle aggregation, it failed to stimulate lipid uptake. rR197A/K201A/K203A was a weak inhibitor for lipid secretion and did not competed with rat [125I]SP-A for receptor occupancy. From these results, we conclude that Lys201 and Lys203 of rat SP-A, and Arg199 and Lys201 of human SP-A are not individually critical for the interaction with lipids and type II cells, and that Glu195 of rat SP-A can be replaced with Gln without loss of SP-A functions. This study also demonstrates that the SP-A-mediated lipid uptake is not directly correlated with phospholipid vesicle aggregation, and that specific interactions of SP-A with type II cells are involved in the lipid uptake process.

Interaction of phospholipid liposomes with plasma membrane isolated from alveolar type II cells: effect of pulmonary surfactant protein A.

Pulmonary surfactant protein A (SP-A) augments the uptake of phospholipid liposomes containing dipalmitoylphosphatidylcholine (DPPC) by alveolar type II cells. The SP-A-mediated uptake process of lipids by type II cells have not been well understood. In the present study we investigated the SP-A-mediated interaction of phospholipids with plasma membrane isolated from alveolar type II cells. SP-A increased the amount of liposomes containing radiolabeled DPPC associated with type II cell plasma membrane by 4-fold compared to the control without SP-A when analyzed by sucrose density gradient centrifugation. This effect is dependent upon the SP-A concentration. The enhancement was inhibited by anti-SP-A antibody and EGTA. When type II cell plasma membrane and liposomes containing [14C]DPPC and [3H]triolein were coincubated with or without SP-A, analysis on sucrose density gradients revealed that the profiles of [14C]DPPC and [3H]triolein in each fraction were almost identical with or without SP-A, indicating that SP-A mediates the binding of liposomes to plasma membrane but not transfer of DPPC. SP-A increased the association of liposomes containing DPPC with the membrane by 2-fold more than that containing 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC). SP-A induced aggregation of phospholipid liposomes containing PLPC as well as those containing DPPC, but the final turbidity of DPPC liposomes aggregated by SP-A was only by 15% greater than that of PLPC liposomes. The amount of DPPC liposomes associated with the plasma membrane derived from type II cells was 2-fold greater than that from liver. We speculate that the SP-A-mediated interaction of lipids with type II cell plasma membrane may contribute, in part, to the lipid uptake process by type II cells.

Differential lipid specificities of the repeated domains of annexin IV.

The roles of the four domains of annexin IV in binding to phospholipids and glycolipids were assessed by analyzing the binding of a group of mutant annexins IV in which one or more of the four domains was inactivated by replacing a critical amino residue(s) (Asp or Glu) with the neutral residue Ala. The data reveal that individual annexin domains may have characteristic affinities for different lipids. In particular, inactivation of the fourth domain inhibits the binding to phosphatidylserine (PS) and phosphatidylinositol (PI) but not to phosphatidylglycerol (PG), suggesting that this domain specifically can accommodate the larger head groups of PS and PI whereas the other three domains may form more restricted binding pockets. In order to block binding to PG, domain 1, or both domains 2 and 3 must be inactivated in addition to domain 4, suggesting that all four domains may be able to accommodate the headgroup of PG to some extent. Binding to acidic glycolipids (sulfatides) was also sensitive to inactivation of domain 4. However, in the case of sulfatides the nature of the binding reaction is fundamentally different compared with the binding to phospholipids since the interaction with sulfatides was highly sensitive to an increase in ionic strength. The binding to sulfatides may depend therefore on charge-charge interactions whereas the binding to phospholipid may involve a more specific interaction between the lipid headgroup and the protein surface, and/or interaction of the protein with the hydrophobic portion of a lipid bilayer.

Follow-up study of atlanto-axial instability in Down's syndrome without separate odontoid process.

Clinical and roentgenologic studies were performed in 69 children with Down's syndrome, without the separate odontoid process, that could be followed for more than 5 years. At the follow-up examination, the atlanto-odontoid process interval (AOI) in flexion, neutral, and extension of the cervical vertebrae significantly decreased when compared with the one at the initial examination. This was particularly obvious up to 5 years of age. Although 14 of 69 cases (20.3%) had atlanto-axial instability at the initial examination, this decreased to four cases (5.8%) at the follow-up examination. However, there were two cases of atlanto-axial instability who were over 10 years of age. There was no significant difference in the minimum sagittal diameter (MSD) at the atlantal level between each position at both the initial and follow-up examinations. Moreover, there was a tendency for the MSD of the cases of positive instability at the follow-up examination to be smaller than those of the cases of negative instability. The degree of ligament laxity improved with increasing age and there was statistically the negative correlation. Although there was a tendency for the AOI to decrease with improvement of the degree of ligament laxity, the correlation could not be confirmed.

Femoral component wear in retrieved hip prostheses.

We retrieved 159 femoral heads at revision surgery to determine changes in surface configuration. Macroscopic wear of the head was observed in three bipolar hip prostheses as a result of three-body wear. There was a considerable change in surface roughness in the internal articulation of bipolar hip prostheses. Roughness in alumina heads was almost the same as that in new cobalt-chromium heads. The annual linear wear rate of polyethylene cups with alumina heads was less than that of cups with cobalt-chromium alloy heads. Polyethylene wear was increased in the prostheses which had increased roughness of the head.

Purification and biochemical characterization of pulmonary surfactant protein A of horses.

OBJECTIVE: To characterize surfactant protein isolated from bronchoalveolar lavage fluids of healthy horses. ANIMALS: 10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) that did not have a history or clinical signs of respiratory tract disease. PROCEDURE: Bronchoalveolar lavage fluid (BALF) was obtained and centrifuged at 33,000 X g. Lipid was removed from precipitated fractions by means of extraction with 1-butanol, and organic solvent-insoluble protein precipitates were dialyzed against Tris buffer. The suspension was centrifuged, and supernatant was placed in a mannose-Sepharose affinity column, with calcium. The bound protein fraction was analyzed by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western immunoblot analysis, and amino acid sequencing. A liposome-aggregation assay was also performed, using purified proteins. RESULTS: Protein isolated by use of mannose-affinity matrices was identified as surfactant protein A (SP-A). It had carbohydrate-binding and phospholipid-aggregation properties characteristic of SP-A isolated from other animal species. The partial primary sequence of the isolated protein had high homology with rat and human SP-A. Furthermore, the equine SP-A reacted with anti-human and anti-rat SP-A specific antibodies. CONCLUSION: Analysis of these findings indicated the existence of SP-A in pulmonary tissues of horses. CLINICAL RELEVANCE: Measurement of SP-A concentrations may be useful for clinicians evaluating pulmonary disease of horses.

Purification and biochemical characterization of equine pulmonary surfactant protein D.

OBJECTIVE: To characterize surfactant protein D (SP-D) isolated from bronchoalveolar lavage fluid (BALF) of healthy horses. SAMPLE POPULATION: BALF from 10 Thoroughbreds (5 males, 5 females; 26 to 40 months old) without history or clinical signs of respiratory tract disease. PROCEDURE: BALF was obtained and centrifuged at 33,000 X g. The supernatant was applied to a mannose-Sepharose 6B affinity column in the presence of calcium, and the bound protein fraction was analyzed by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblot analysis; amino acid composition was determined and partial sequencing was done. Phospholipid binding and liposome aggregation assay were performed, using purified proteins. RESULTS: The protein isolated by use of mannose affinity matrices was SP-D. It bound carbohydrates and phosphatidylinositol, which are the characteristic features of SP-D isolated from other animal species. Amino acid analysis and partial primary sequence of the isolated protein indicated high homology with rat and human SP-D. Furthermore, immunoblot analysis indicated that equine SP-D reacted with human and rat SP-D-specific antibodies. CONCLUSION AND CLINICAL RELEVANCE: SP-D exists in equine lungs; its measurement may be useful in evaluating equine lung disease.

Diagnostic accuracy of microcomputed tomography for osseous abnormalities in the rat temporomandibular joint condyle.

OBJECTIVES: Our aim was to investigate the diagnostic accuracy of in vivo micro-CT for osseous abnormalities of the rat temporomandibular joint (TMJ) condyle, using macroscopic observations as the "gold standard". METHODS: A 30 TMJ arthritis model was prepared by injecting inflammatory complete Freund's adjuvant (CFA) into one side of the TMJ cavities of rats. The TMJ condyles were then imaged using micro-CT. The samples were macroscopically evaluated for osseous abnormalities, including erosions, osteophytes, flattening and concavity. The micro-CT images were independently assessed for abnormalities using the same criteria. Images in three planes were produced using the micro-XYZ technique with the micro-CT equipment. RESULTS: According to the macroscopic observations, 26 of the 60 rat condyles showed osseous abnormalities. The micro-XYZ images detected abnormalities in 25 of the condyles. The condyle diagnostic accuracy of micro-CT was 0.98, the sensitivity was 0.96 and the specificity was 1.0. CONCLUSIONS: Good diagnostic results were obtained using micro-CT. It is therefore an effective technique for the evaluation of osseous abnormalities in the rat TMJ condyle.

Reproducibility and accuracy of measuring unerupted teeth using limited cone beam X-ray CT.

OBJECTIVE: The purpose of this investigation was to determine the reproducibility among observers and accuracy of the measurement of the tooth crown width of unerupted teeth using limited area cone beam X-ray CT. METHODS: 3DX multi-image micro-CT (3DX, Morita Co., Kyoto, Japan) images of impacted supernumerary teeth in the median maxillary region taken prior to extraction were used for the samples. The width of the tooth on the 3DX image was measured five times by five individual observers. Significant differences in values among the observers in the measurement were determined by one-way analysis of variance for examining reproducibility. The measurement results of the ten samples on 3DX images were compared with the laboratory measurements using a three-dimensional co-ordinate measuring apparatus, using the Wilcoxon signed-rank sum test. RESULTS: There was no significant difference among the observers in the measurement (P>0.05). The measurement results shown on 3DX images were significantly larger than those of the laboratory measurements (P<0.05). The mean difference was +0.088 mm. CONCLUSIONS: 3DX has high reproducibility for measuring the tooth crown width of unerupted teeth. While 3DX measurement values were larger than the laboratory measurements, the difference is clinically insignificant.

Relationship between patient characteristics, mandibular head morphology and thickness of the roof of the glenoid fossa in symptomatic temporomandibular joints.

OBJECTIVE: The purpose of this clinical study was to investigate the minimum thickness of the roof of the glenoid fossa (RGF) of grossly normal temporomandibular joints (TMJ) and to correlate this with patient gender, age and the morphological classification of the mandibular head. METHODS: The study was performed on 191 TMJs from 109 patients (25 male and 84 female, age range 3-79 years, mean age 28.1 years) who visited Nihon University Dental Hospital, Japan with suspected TMJ disorders. The patients underwent cone beam computed tomography (3DX CT) to enable observation of the morphological features of the mandibular head. The minimum thickness of the RGF was measured using frontal section images acquired by CT. The morphology of the mandibular heads was classified according to the method of Yale and colleagues. Mean linear measurements were used for statistical analyses of patient gender, age and mandibular head morphology. RESULTS: The average minimum thickness of the RGF was 0.79 mm. No significant difference in thickness was found between male and female patients. In addition, no differences were recorded as a result of variation in age or mandibular head morphology. CONCLUSIONS: These results indicate that RGF thickness is not significantly correlated with gender, age, or mandibular head morphology, at least in this cohort of patients.

Roles of collagenous domain and oligosaccharide moiety of pulmonary surfactant protein A in interactions with phospholipids.

Pulmonary surfactant protein A (SP-A), a main component of lung-specific lipid-protein complex (pulmonary surfactant), is characterized by a collagen-like sequence in its amino terminal half and by N-linked glycosylation. The structural characteristics necessary for the various functions of SP-A are not yet completely understood. In the present study we examined the roles of the oligosaccharide moiety of SP-A and its collagenous domain in causing the aggregation of phospholipid liposomes and enhancing the uptake of phospholipids by type II cells. SP-A in the deglycosylated form increased turbidity, measured to evaluate liposome aggregation, to some extent at 400 nm, but this ability of the deglycosylated protein appeared to be less than that of control SP-A. The collagenase-resistant fragment of SP-A completely failed to aggregate phospholipid liposomes. Deglycosylated SP-A was able to enhance the uptake of phospholipids by type II cells, whereas removal of the collagenous domain of SP-A resulted in the loss of the ability to enhance phospholipid uptake.

Pulmonary surfactant protein A-mediated uptake of phosphatidylcholine by alveolar type II cells.

Pulmonary surfactant protein A (SP-A)-mediated uptake of phosphatidylcholine (PC) by alveolar type II cells was investigated. SP-A enhanced the uptake of liposomes containing dipalmitoylphosphatidylcholine (DPPC), 1-palmitoyl-2-linoleoyl phosphatidylcholine (PLPC), or 1,2-dihexadecyl-sn-glycero-3-phosphocholine (DPPC-ether), a diether analogue of DPPC, but about twice as much DPPC was taken up by type II cells as PLPC or DPPC-ether. When subcellular distribution was analyzed, 51.3 +/- 2.9% (mean +/- SD, n = 3) of cell-associated radiolabeled DPPC was recovered in the lamellar body-rich fraction in the presence of SP-A, whereas only 19.3 +/- 1.9% (mean +/- SD, n = 3) was found to this fraction in the absence of SP-A. When type II cells were incubated either with DPPC at 0 degree C or with DPPC-ether at 37 degrees C, or no cells were included, low proportions of the cell-associated lipids were present in the fractions corresponding to lamellar bodies even in the presence of SP-A. Anti-SP-A antibody significantly reduced the radioactivity incorporated into the lamellar body fraction. Phosphatidylcholine that had been incorporated into lamellar bodies remained largely intact when SP-A was present. Subcellular fractionations of type II cells with radiolabeled SP-A and DPPC revealed that the sedimentation characteristics of cell-associated SP-A are different from those of DPPC, although a small broad peak of radiolabeled SP-A was found in the lamellar body fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary surfactant protein D specifically binds to phosphatidylinositol.

Alveolar type II cells produce and secrete a complex mixture of lipids and proteins called pulmonary surfactant of which phospholipids are the major components. Surfactant proteins (SP) A, B, and C interact with phospholipids and are believed to play important roles in alveolar spaces. However, whether surfactant protein D (SP-D) interacts with phospholipids is unknown. In the present study, we examined whether SP-D binds to phospholipids and investigated phospholipid specificities of SP-D binding and the structural requirements of phospholipids for that binding using 125I-SP-D as a probe. 125I-SP-D bound exclusively to phosphatidylinositol (PI) in various phospholipids or a fraction containing phospholipids extracted from surfactant, which were developed on thin layer chromatography. 125I-SP-D also bound to PI coated on microtiter wells in a manner dependent upon the SP-D concentration. Unlabeled SP-D competed well with 125I-SP-D for PI binding and the antibody against SP-D abolished 125I-SP-D binding to PI. PI liposome also attenuated 125I-SP-D binding to the solid phase PI. Ca2+ is absolutely required for the binding of SP-D to PI. SP-D failed to bind to lyso-PI, fatty acids derived from PI digested with phospholipase A2, or diacylglycerol obtained after phospholipase C treatment of PI. SP-D bound to neither phosphatidylinositol 4-monophosphate nor phosphatidylinositol 4,5-diphosphate. We conclude that SP-D specifically binds to PI. This is the first report that demonstrates that SP-D interacts with surfactant phospholipids.

Calcium and dithiothreitol dependent conformational changes in beta-sheet structure of collagenase resistant fragment of human surfactant protein A.

Ca2+ dependent conformational change of collagenase resistant fragment (CRF) of human surfactant protein A (SP-A) was studied by measurements of the far UV circular dichroism spectrum. The spectrum was altered by Ca2+ and DTT. The beta-sheet content was decreased by the addition of Ca2+ from 28.1 to 26.6%. On the other hand, the beta-sheet content was increased in the presence of dithiothreitol from 28.1 to 36.0%, and decreased by the addition of Ca2+ from 36.0 to 30.5%. The total Ca2+ concentration required for half maximal change of the ellipticity at 220 nm was estimated to be 30 microM both in the presence and absence of dithiothreitol. One of the functions of SP-A, enhancement of phospholipid uptake by alveolar type II cells, was abolished by the addition of 2-mercaptoethanol. These results strongly indicate a relationship between the conformation of CRF and SP-A functions.

Cerebro-costo-mandibular syndrome. A case report and review of the literature.

A 7-month-old boy with the cerebro-costo-mandibular syndrome is presented. This is the first case report in an Oriental population. 15 reported cases in the literature are reviewed.

The "happy puppet" syndrome in two siblings.

Two siblings with the "happy puppet" syndrome are presented. Their clinical features are quite similar and closely resemble those of previously reported cases. These features include severe mental retardation, epileptic seizures, easily provoked and prolonged paroxysms of laughter, atactic jerky movements, hypotonia, large mandible with prognathia, and 2-3 cps spike and wave activity in the EEG. The occurrence of this syndrome in the two siblings suggests a genetic etiology possible as an autosomal recessive trait.

Familial retinoblastoma (mother and son) with 13q14 deletion.

We present here the first familial cases (a mother and son) of dominantly inherited retinoblastoma with a 13q14 deletion [46,XY or XX, del(13)(q14.1q21.2)]. Their esterase D activities in red blood cells were as low as 50% of the normal control and the haplotype of esterase D was a type 1-0 in the mother and a type 2-0 in the son. They had peculiar facies characterized by a high forehead, low and broad nasal root, a short and bulbous nose, a long philtrum, and open mouth with a thin upper lip, and prominent earlobes. Chromosome and esterase D analysis should be performed in patients with retinoblastoma even if retinoblastoma seems to be transmitted through an autosomal dominant inheritance. This family indicates that one of the causes of dominantly inherited retinoblastoma is a chromosome deletion of part of the 13q14 band whether it is detectable by chromosome analysis or not.

Human surfactant protein A with two distinct oligomeric structures which exhibit different capacities to interact with alveolar type II cells.

The lung lavage fluids from patients with pulmonary alveolar proteinosis have been generally used as a source for human surfactant protein A (SP-A). We have recently found that a multimerized form of SP-A oligomer (alveolar proteinosis protein-I, APP-I) exists besides the normal-sized octadecamer (APP-II) in SP-As isolated from the patients. When analysed by Bio-Gel A15m column chromatography in 5 mM Tris buffer (pH 7.4), the apparent molecular masses of APP-I and APP-II were 1.65 MDa and 0.93 MDa, respectively. Gel-filtration analysis also revealed that APP-II is clearly separated from APP-I in the presence of 2 mM Ca2+ and 150 mM NaCI. We investigated the abilities of both SP-A oligomers to regulate phospholipid secretion and to bind to alveolar type II cells. Although APP-I inhibited lipid secretion, it was clearly a less effective inhibitor than APP-II. IC50 for inhibition of lipid secretion was apparently 0.23 +/- 0.08 microgram/ml (0.14 +/- 0.05 nM) and 0.055 +/- 0.019 microgram/ml (0.059 +/- 0.020 nM) for APP-I and APP-II, respectively. Both proteins bound to monolayers of type II cells in a concentration-dependent manner; however, APP-I clearly had a lower affinity to bind to type II cells. The apparent dissociation contants were, K(d) = 2.31 +/- 0.70 microgram/ml (1.40 +/- 0.43 nM) and 0.89 +/- 0.22 microgram/ml (0.95 +/- 0.24 nM) for APP-I and APP-II, respectively. Excess unlabelled rat SP-A replaced 45% of 125I-APP-I and 77% of 125I-APP-II for type II cell binding. Although 125I-APP-II competed with excess unlabelled APP-I or APP-II, 125I-APP-I failed to compete and instead its binding rather increased in the presence of unlabelled APPs. The biotinylated APP-I bound to APP-I and APP-II coated on to microtitre wells in a concentration-dependent manner, indicating that APP-I interacts with APPs. This study demonstrates that the multimerized form of human SP-A oligomer exhibits the following attributes: (1) the reduced capacity to regulate phospholipid secretion from type II cells, and (2) lower affinity to bind to type II cells, and that the integrity of a flower-bouquet-like octadecameric structure of SP-A oligomer is important for the expression of full activity of this protein, indicating the importance of the oligomeric structure of mammalian lectins with collagenous domains.

Epitope mapping for monoclonal antibodies identifies functional domains of pulmonary surfactant protein A that interact with lipids.

Pulmonary surfactant protein A (SP-A) contains 4 domains: a disulfide forming amino terminus, a collagen-like region, a neck region, and a carbohydrate recognition region. The protein binds the lipids dipalmitoylphosphatidylcholine and galactosylceramide and induces aggregation of phospholipid vesicles. SP-A also inhibits lipid secretion and enhances the uptake of phospholipid by alveolar type II cells. Previously described monoclonal antibody 1D6 blocks the inhibitory effect of SP-A on lipid secretion by type II cells, but antibody 6E3 has no effect. In the present study we mapped the epitopes for monoclonal antibodies 1D6 and 6E3 by enzyme-linked immunoassay of recombinant proteins expressed using the baculovirus system, and investigated the domain that is responsible for the SP-A interactions with lipid. Monoclonal antibody 1D6 bound to mutant SP-As in which the neck portion of the molecule was deleted or substituted with that of mannose-binding protein A, but 6E3 failed to bind to these mutants. In contrast, 1D6 did not bind to a chimera in which the carbohydrate recognition domain (CRD) was substituted with that of surfactant protein D (SP-D). In addition, 1D6 failed to recognize antigen in cells infected with the recombinant virus directing the synthesis of a Cys204-Cys218 (small disulfide loop) deletion within the CRD. Antibody 1D6 completely blocked the binding of SP-A to dipalmitoylphosphatidylcholine and galactosylceramide and liposome aggregation. By comparison, 6E3 failed to completely attenuate the interactions of SP-A with lipids. However, both 6E3 and 1D6 blocked the uptake of lipid by type II cells that is caused by SP-A. From these data, we conclude that: 1) the epitope for antibody 6E3 is located at the neck domain of SP-A and that for antibody 1D6 is at the small loop region in the CRD; 2) the CRD is essential for the SP-A functions of lipid binding, liposome aggregation, the inhibitory effect on lipid secretion, and the augmentation of lipid uptake by type II cells, and these activities are largely attributable to amino acid residues within the steric inhibitory footprint of 1D6 bound to the small disulfide loop region; and 3) the neck domain of SP-A may also be involved in the process of SP-A-mediated uptake of phospholipids by alveolar type II cells.