title: Reduced gravity evaluation of potential spaceflight-compatible flow cytometer technology.
abstract: BACKGROUND
  The presence of a spaceflight-compatible flow cytometer onboard the International Space Station would be extremely beneficial for in-flight medicine and reduced gravity research. In the past, commercially available flow cytometers were not suitable for use during spaceflight due to their size, weight, power, and sheath fluid requirements. Recent advances in cytometer technology have enabled features that now make a spaceflight-compatible cytometer possible. We evaluated a small, robust novel cytometer with design features that minimize or eliminate many incompatibilities with spaceflight. This cytometer is highly miniaturized and lightweight, does not require sheath fluid, and uses a low-energy diode laser. The ability to achieve laminar particle flow without sheath fluid is important because an instrument using large liquid volumes and producing an equivalent amount of hazardous liquid waste would not meet spaceflight constraints.
  
  
  METHODS
  For this study the cytometer was modified so that stained liquid cell samples could be delivered during reduced gravity. The cytometer was then evaluated onboard the NASA KC-135 reduced gravity research aircraft. The KC-135 uses a parabolic flight path to generate essentially zero gravity conditions for 30-s increments. Typically 40 parabolas are flown per mission, resulting in approximately 20 min of reduced gravity during which research may be performed. During this evaluation, bead-based cytometer precision, photomultiplier tube linearity, and leukocyte immunophenotype analysis were performed during reduced gravity. The flight data were then compared with ground-based control data and data generated using a reference cytometer (Beckman-Coulter XL).
  
  
  RESULTS
  This novel cytometer functioned well during reduced gravity and produced data comparable to those of ground-based controls with only minor caveats. The reduced gravity cell immunophenotype data were indistinguishable from ground control data and reference cytometric data. Bead-based instrument precision (coefficient of variation) was slightly increased during reduced gravity operation, but not to a degree that would affect most common flow cytometric applications. The ability of the instrument to collect absolute cell counts was validated.
  
  
  CONCLUSIONS
  This study represents the first generation of real-time flow cytometry data during zero gravity. With modifications, the evaluated cytometer technology could be the basis from which an operational spaceflight-compatible flow cytometer is developed.
authors.affiliation: Wyle Laboratories, Space Physiology and Countermeasures Department, Houston, Texas 77058, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Crucian
authors.forename: Clarence
authors.initials: C
authors.lastname: Sams
mesh_terms: D000328:Adult; D017252:CD3 Complex / Q000097:blood; D015704:CD4 Antigens / Q000097:blood; D002469:Cell Separation / Q000379:methods; D005434:Flow Cytometry / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D006801:Humans; D018472:Hypogravity; D016130:Immunophenotyping / Q000379:methods; D007958:Leukocyte Count / Q000379:methods; D013026:Space Flight; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D017252:CD3 Complex; D015704:CD4 Antigens