title: In vitro apoptosis in peripheral blood mononuclear cells induced by low-dose radiotherapy displays a discontinuous dose-dependence.
abstract: OBJECTIVE
  Cells undergoing apoptosis contribute to the regulation of activated mononuclear cells (Voll et al. 1997). Low-dose radiotherapy (LD-RT) is known to improve inflammatory symptoms, but the mechanism of action is still unclear. The aim of this study was to investigate the rate of apoptosis of peripheral blood mononuclear cells (PBMC) induced by LD-RT within the therapeutic dose range of anti-inflammatory RT.
  
  
  METHODS
  PBMC were isolated from venous blood of ten healthy volunteers and were irradiated with single doses between 0.1 and 3.0 Gy. Apoptotic nuclei were detected by flow cytometry after propidium iodide (PI) triton staining, and apoptotic cells were detected by annexin V/PI staining and cell scatter analysis. Since apoptotic cells display increased cytoplasmatic granularity and concomitant reduced cell size, they can be distinguished from viable cells in forward/side scatter (FSC/SSC) histograms. Apoptotic PBMC were further subtyped by double staining with annexin V and directly labelled monoclonal antibodies recognizing the lineage-specific surface markers CD4, CD8, and CD19, respectively. The apoptosis rate of irradiated cells was analysed in a time and dose dependent fashion and was compared to a sham-irradiated control.
  
  
  RESULTS
  After irradiation, a dose-dependent increase in apoptosis was observed, with a discontinuity (plateau or peak) between 0.3Gy and 0.7Gy in 9/10 donors (90%) and 59/80 samples (74%). 8/10 donors (80%) and 38/80 samples (47%) showed not only a discontinuous increase with a plateau but a relative maximum of apoptosis peaking within the dose range of 0.3 Gy and up to 0.7 Gy.
  
  
  CONCLUSIONS
  LD-RT induces a relative maximum of apoptosis in PBMC in the does range between 0.3 Gy and 0.7 Gy. This may contribute to its anti-inflammatory effect observed clinically.
authors.affiliation: Department for Clinical Immunology and Rheumatology, Institute for Clinical Immunology and Rheumatology of the Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Kern
authors.forename: L
authors.initials: L
authors.lastname: Keilholz
authors.forename: C
authors.initials: C
authors.lastname: Forster
authors.forename: M H
authors.initials: MH
authors.lastname: Seegenschmiedt
authors.forename: R
authors.initials: R
authors.lastname: Sauer
authors.forename: M
authors.initials: M
authors.lastname: Herrmann
mesh_terms: D000328:Adult; D015703:Antigens, CD / Q000032:analysis; D017209:Apoptosis; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007249:Inflammation / Q000532:radiotherapy; D008214:Lymphocytes / Q000276:immunology / Q000528:radiation effects*; D008297:Male; D011879:Radiotherapy Dosage
chemical_list: D015703:Antigens, CD