We tested the hypothesis whether allergic airway inflammation in ovalbumin sensitized and challenged Brown Norway rats is associated with intrinsic surfactant alteration and dysfunction. The determination of intra-alveolar surfactant subtypes and alveolar edema within their original microenvironment is only possible using an ultrastructural stereological approach. Therefore both lungs of control and asthmatic rats were fixed by vascular perfusion. The volume fractions of surfactant subtypes and the epithelial surface fraction covered with alveolar edema were determined by point and intersection counting. Furthermore, lung resistance was measured by means of whole-body plethysmography. The surface activity of surfactant from bronchoalveolar lavage was determined as minimum surface tension at minimal bubble size with a pulsating bubble surfactometer. Compared with controls, in asthmatics (1) the fraction of inactive unilamellar forms was significantly increased from 56% to 66%, (2) the fraction of alveolar epithelium covered with alveolar edema visible by light microscopy was significantly increased from 0.7% to 5.0%, (3) the fraction of alveolar epithelium covered with fluid seen by electron microscopy expanded significantly from 5% to 21%, (4) lung resistance was significantly elevated from 14% to 86% and (5) surface tension was enhanced from 6 mN/m to 12 mN/m. Thus, the inflammatory process after allergen challenge of sensitized Brown Norway rats causes intra-alveolar surfactant alterations. These surfactant alterations might contribute to small airway dysfunction.
In this study we test the hypothesis that endogenous particles in exhaled air (PEx), non-invasively sampled from lower airways, are well suited for the analysis of respiratory tract lining fluid (RTLF) proteins, i.e., surfactant protein A (SP-A) and albumin. Ten healthy volunteers were included in the study and participated in two sampling sessions. Blood, exhaled breath condensate (EBC) and PEx were collected at each session. 100 L of breath were collected for each exhaled sample. Serum and exhaled samples were analyzed for SP-A using an in-house ELISA. Albumin was analyzed in exhaled samples using a commercial ELISA kit. SP-A detection rates were 100%, 21%, and 89% for PEx, EBC and serum, respectively. Albumin was detected in PEx, but not in EBC. SP-A measurements in PEx showed good repeatability with an intra-individual coefficient of variation of 13%. Both SP-A and albumin showed significant correlation to mass of PEx (r(s) = 0.93, p
Variation in surfactant protein D (SP-D) is associated with lung function in tobacco smoke-induced chronic respiratory disease. We hypothesized that the same association exists in the general population and could be used to identify individuals sensitive to smoke-induced lung damage. The association between serum SP-D (sSP-D) and expiratory lung function was assessed in a cross-sectional design in a Danish twin population (n = 1,512, 18-72 yr old). The adjusted heritability estimates for expiratory lung function, associations between SP-D gene (SFTPD) single-nucleotide polymorphisms or haplotypes, and expiratory lung function were assessed using twin study methodology and mixed-effects models. Significant inverse associations were evident between sSP-D and the forced expiratory volume in 1 s and forced vital capacity in the presence of current tobacco smoking but not in nonsmokers. The two SFTPD single-nucleotide polymorphisms, rs1923536 and rs721917, and haplotypes, including these single-nucleotide polymorphisms or rs2243539, were inversely associated with expiratory lung function in interaction with smoking. In conclusion, SP-D is phenotypically and genetically associated with lung function measures in interaction with tobacco smoking. The obtained data suggest sSP-D as a candidate biomarker in risk assessments for subclinical tobacco smoke-induced lung damage. The data and derived conclusion warrant confirmation in a longitudinal population following chronic obstructive pulmonary disease initiation and development.
Surfactant protein (SP) A and SP-D are collectins that have roles in host defense. The Eustachian tube (ET) maintains the patency between the upper airways and the middle ear. Dysfunction of local mucosal immunity in ET may predispose infants to recurrent otitis media. We recently described preliminary evidence of the expression of SP-A and SP-D in the ET. Our present aim was to establish the sites of SP-A and SP-D expression within the epithelium of the ET in vivo. With in situ hybridization, electron microscopy, and immunoelectron microscopy, the cells responsible for SP-A and SP-D expression and storage were identified. SP-A expression was localized within the ET epithelium, and the protein was found in the electron-dense granules of microvillar epithelial cells. Being concentrated in the epithelial lining, only a few cells revealed intracellular SP-D, and it was not associated with granules. The SP-A and SP-D immunoreactivities in ET lavage fluid, as shown by Western blot analyses, were similar to those in bronchoalveolar lavage fluid. We propose that there are specialized cells in the ET epithelium expressing and secreting SP-A and SP-D. SP-A and SP-D may be important for antibody-independent protection of the middle ear against infections.