title: Brain radiation injury leads to a dose- and time-dependent recruitment of peripheral myeloid cells that depends on CCR2 signaling.
abstract: BACKGROUND
  Cranial radiotherapy is used to treat tumors of the central nervous system (CNS), as well as non-neoplastic conditions such as arterio-venous malformations; however, its use is limited by the tolerance of adjacent normal CNS tissue, which can lead to devastating long-term sequelae for patients. Despite decades of research, the underlying mechanisms by which radiation induces CNS tissue injury remain unclear. Neuroinflammation and immune cell infiltration are a recognized component of the CNS radiation response; however, the extent and mechanisms by which bone marrow-derived (BMD) immune cells participate in late radiation injury is unknown. Thus, we set out to better characterize the response and tested the hypothesis that C-C chemokine receptor type 2 (CCR2) signaling was required for myeloid cell recruitment following brain irradiation.
  
  
  METHODS
  We used young adult C57BL/6 male bone marrow chimeric mice created with donor mice that constitutively express enhanced green fluorescent protein (eGFP). The head was shielded to avoid brain radiation exposure during chimera construction. Radiation dose and time response studies were conducted in wild-type chimeras, and additional experiments were performed with chimeras created using donor marrow from CCR2 deficient, eGFP-expressing mice. Infiltrating eGFP+ cells were identified and quantified using immunofluorescent microscopy.
  
  
  RESULTS
  Brain irradiation resulted in a dose- and time-dependent infiltration of BMD immune cells (predominately myeloid) that began at 1 month and persisted until 6 months following ≥15 Gy brain irradiation. Infiltration was limited to areas that were directly exposed to radiation. CCR2 signaling loss resulted in decreased numbers of infiltrating cells at 6 months that appeared to be restricted to cells also expressing major histocompatibility complex class II molecules.
  
  
  CONCLUSIONS
  The potential roles played by infiltrating immune cells are of current importance due to increasing interest in immunotherapeutic approaches for cancer treatment and a growing clinical interest in survivorship and quality of life issues. Our findings demonstrate that injury from brain radiation facilitates a dose- and time-dependent recruitment of BMD cells that persists for at least 6 months and, in the case of myeloid cells, is dependent on CCR2 signaling.
authors: Department of Radiation Oncology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. michael_moravan@urmc.rochester.edu.
authors: Michael J
authors: MJ
authors: Moravan
authors: Department of Neuroscience, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. john_olschowka@urmc.rochester.edu.
authors: John A
authors: JA
authors: Olschowka
authors: Department of Radiation Oncology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. jackie_williams@urmc.rochester.edu.|Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. jackie_williams@urmc.rochester.edu.
authors: Jacqueline P
authors: JP
authors: Williams
authors: Department of Neuroscience, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. kerry_obanion@urmc.rochester.edu.|Department of Neurology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. kerry_obanion@urmc.rochester.edu.
authors: M Kerry
authors: MK
authors: O'Banion
mesh_terms: D000818:Animals; D016026:Bone Marrow Transplantation; D001930:Brain Injuries / Q000209:etiology* / Q000473:pathology*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D005786:Gene Expression Regulation / Q000528:radiation effects; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008840:Microfilament Proteins / Q000378:metabolism; D022423:Myeloid Cells / Q000528:radiation effects*; D018995:Myosin Heavy Chains / Q000378:metabolism; D020556:Neutrophil Infiltration / Q000528:radiation effects; D011828:Radiation Chimera / Q000502:physiology; D011832:Radiation Injuries / Q000150:complications*; D054390:Receptors, CCR2 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000528:radiation effects*; D013997:Time Factors
chemical_list: C491049:Aif1 protein, mouse; D002135:Calcium-Binding Proteins; C515335:Ccr2 protein, mouse; D016207:Cytokines; D008840:Microfilament Proteins; D054390:Receptors, CCR2; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D018995:Myosin Heavy Chains