title: Changes in the levels of mannan-binding lectin and ficolins during head-down tilted bed rest.
abstract: BACKGROUND
  Spaceflight studies and ground-based analogues of microgravity indicate a weakening of human immunity. Mannan-binding lectin (MBL) and H-, L-, and M-ficolin together constitute the lectin pathway and mediate the clearance of pathogens through complement activation. We hypothesized that simulated microgravity may weaken human innate immune functions and studied the impact of 6° head-down tilted bed rest (HDT) for 21 d on MBL and ficolin levels.
  
  
  METHODS
  Within a 6-mo period, seven men underwent two periods of HDT. Blood samples were analyzed for MBL, H-, L-, and M-ficolin, mannose-binding lectin-associated protein of 44 kDa (MAp44), and collectin liver 1 (CL-L1) by time-resolved immunofluorometric assays (TRIFMA).
  
  
  RESULTS
  We observed well-defined individual preintervention levels of MBL and ficolins. Remarkably similar intraindividual changes occurred for MBL and MBL levels decreased (mean 282 ng · ml⁻¹) in the recovery phase. Conversely, CL-L1, a protein with MBL-like properties, increased (mean 102 ng · ml⁻¹) during the recovery phase. M-ficolin increased (mean 79 ng · ml⁻¹) within the first 2 d of HDT, followed by a decrease (mean 112 ng · ml⁻¹) during the recovery phase. L-ficolin increased (mean 304 ng · ml⁻¹) during HDT, while H-ficolin was essentially unaffected. MAp44, a down-regulator of the lectin pathway, decreased initially (mean 78 ng · ml⁻¹) in the recovery phase followed by an increase (mean 131 ng · ml⁻¹).
  
  
  CONCLUSIONS
  Alterations in MBL and ficolin levels were modest and with our current knowledge do not lead to overt immunodeficiency. Pronounced changes occurred when the subjects resumed the upright position. In selected individuals, these changes appear to be a conserved response to HDT.
authors.affiliation: Department of Medicine, Randers Regional Hospital, Randers, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Kelsen
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Sandahl
authors.forename: Line
authors.initials: L
authors.lastname: Storm
authors.forename: Petra
authors.initials: P
authors.lastname: Frings-Meuthen
authors.forename: Jens F
authors.initials: JF
authors.lastname: Dahlerup
authors.forename: Steffen
authors.initials: S
authors.lastname: Thiel
mesh_terms: D000328:Adult; D001510:Bed Rest; D015415:Biomarkers / Q000097:blood; D037222:Collectins / Q000097:blood; D018592:Cross-Over Studies; D015200:Fluoroimmunoassay; D018475:Head-Down Tilt; D006801:Humans; D037102:Lectins / Q000097:blood*; D008297:Male; D037601:Mannose-Binding Lectin / Q000097:blood*; D050606:Mannose-Binding Protein-Associated Serine Proteases / Q000378:metabolism; D014893:Weightlessness; D000097604:Ficolins
chemical_list: D015415:Biomarkers; D037222:Collectins; D037102:Lectins; D037601:Mannose-Binding Lectin; D050606:Mannose-Binding Protein-Associated Serine Proteases; D000097604:Ficolins; C445459:COLEC10 protein, human; C084067:MASP1 protein, human