Variable hematopoietic responses to acute photons, protons and simulated solar particle event protons.
The goal of this study was to evaluate, for the first time, the response of bone marrow-derived cell populations to protons mimicking a space radiation environment.


METHODS
C57BL/6 mice were exposed to 2 Gray (Gy) simulated solar particle event protons (sSPE) over 36 h; energies ranged from 15 to 215 MeV/n and were administered in 10 MeV increments. Acute 2 Gy irradiation with photons (gamma-rays) and protons were administered to different groups at 0.7 Gy/min and 0.9 Gy/min, respectively, for comparison with sSPE. The animals were euthanized on days 4 and 21 post-exposure for analyses.


RESULTS
Exposure to radiation, regardless of regimen, resulted in immune depression and other abnormalities in cell populations residing in the blood and spleen; the extent of the radiation damage was somewhat dependent upon body compartment and time postexposure. However, variations were also noted among the three radiation regimens in a number of measurements: relative spleen mass, basal DNA synthesis by leukocytes, white blood cell counts and three-part differentials (lymphocytes, granulocytes, monocytes-macrophages), lymphocyte subpopulations (CD4+ T, CD8+ T, B and NK cells) and erythrocyte and thrombocyte characteristics.


CONCLUSIONS
The data demonstrate that exposure to proton radiation mimicking a solar explosion induces abnormalities in leukocytes, erythrocytes and platelets that may have adverse health consequences. However, the damaging effects of sSPE on leukocytes and platelets were generally less pronounced compared to the other radiation regimens. Results obtained with photons (gamma-rays, X-rays) and monoenergetic protons at space-relevant total doses may not necessarily predict biological responses after exposure to a solar particle event.
Gridley
Daila S
DS
Department of Radiation Medicine, Loma Linda University, Loma Linda, CA 92354, USA. dgridley@dominion.llumc.edu
Rizvi
Asma
A
Luo-Owen
Xian
X
Makinde
Adeola Y
AY
Coutrakon
George B
GB
Koss
Peter
P
Slater
James M
JM
Pecaut
Michael J
MJ
D000818:Animals; D001792:Blood Platelets / Q000528:radiation effects; D003359:Cosmic Radiation; D004247:DNA / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D004912:Erythrocytes / Q000528:radiation effects; D006413:Hematopoietic System / Q000528:radiation effects*; D007962:Leukocytes / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D017785:Photons; D011522:Protons / Q000009:adverse effects*; D011832:Radiation Injuries; D019445:Solar Activity; D018561:Space Simulation / Q000379:methods*; D013154:Spleen / Q000528:radiation effects; D013997:Time Factors
D011522:Protons; D004247:DNA