title: Distinct compartmentalization of SP-A and SP-D in the vasculature and lungs of patients with idiopathic pulmonary fibrosis.
abstract: BACKGROUND
  Surfactant proteins SP-A and SP-D are useful biomarkers in diagnosis, monitoring, and prognosis of idiopathic pulmonary fibrosis (IPF). Despite their high structural homology, their serum concentrations often vary in IPF patients. This retrospective study aimed to investigate distinct compartmentalization of SP-A and SP-D in the vasculature and lungs by bronchoalveolar lavage fluid (BALF)/serum analysis, hydrophilicity and immunohistochemistry.
  
  
  METHODS
  We included 36 IPF patients, 18 sarcoidosis (SAR) patients and 20 healthy subjects. Low-speed centrifugal supernatants of BALF (Sup-1) were obtained from each subject. Sera were also collected from each patient. Furthermore, we separated Sup-1 of IPF patients into hydrophilic supernatant (Sup-2) and hydrophobic precipitate (Ppt) by high-speed centrifugation. We measured SP-A and SP-D levels of each sample with the sandwich ELISA technique. We analyzed the change of the BALF/serum level ratios of the two proteins in IPF patients and their hydrophilicity in BALF. The distribution in the IPF lungs was also examined by immunohistochemical staining.
  
  
  RESULTS
  In BALF, SP-A levels were comparable between the groups; however, SP-D levels were significantly lower in IPF patients than in others. Although IPF reduced the BALF/serum level ratios of the two proteins, the change in concentration of SP-D was more evident than SP-A. This suggests a higher disease impact for SP-D. Regarding hydrophilicity, although more than half of the SP-D remained in hydrophilic fractions (Sup-2), almost all of the SP-A sedimented in the Ppt with phospholipids. Hydrophilicity suggests that SP-D migrates into the blood more easily than SP-A in IPF lungs. Immunohistochemistry revealed that SP-A was confined to thick mucus-filling alveolar space, whereas SP-D was often intravascular. This data also suggests that SP-D easily leaks into the bloodstream, whereas SP-A remains bound to surfactant lipids in the alveolar space.
  
  
  CONCLUSIONS
  The current study investigated distinct compartmentalization of SP-A and SP-D in the vasculature and lungs. Our results suggest that serum levels of SP-D could reflect pathological changes of the IPF lungs more incisively than those of SP-A.
authors.forename: Hirotaka
authors.initials: H
authors.lastname: Nishikiori
authors.affiliation: Department of Respiratory Medicine and Allergology, Sapporo Medical University School of Medicine, South-1 West-17, Chuo-ku, Sapporo 060-8556, Japan. hchiba@sapmed.ac.jp.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Chiba
authors.forename: Shigeru
authors.initials: S
authors.lastname: Ariki
authors.forename: Koji
authors.initials: K
authors.lastname: Kuronuma
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Otsuka
authors.forename: Masanori
authors.initials: M
authors.lastname: Shiratori
authors.forename: Kimiyuki
authors.initials: K
authors.lastname: Ikeda
authors.forename: Atsushi
authors.initials: A
authors.lastname: Watanabe
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kuroki
authors.forename: Hiroki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000032:analysis; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry*; D004730:Endothelium, Vascular / Q000737:chemistry*; D005260:Female; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D054990:Idiopathic Pulmonary Fibrosis / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D011650:Pulmonary Alveoli / Q000737:chemistry*; D037662:Pulmonary Surfactant-Associated Protein A / Q000032:analysis* / Q000097:blood; D037663:Pulmonary Surfactant-Associated Protein D / Q000032:analysis* / Q000097:blood; D012189:Retrospective Studies; D012507:Sarcoidosis / Q000378:metabolism
chemical_list: D015415:Biomarkers; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D