Compartmental responses after thoracic irradiation of mice: strain differences.
OBJECTIVE
To examine and compare the molecular and cellular processes leading to radiation fibrosis and pneumonitis in C57BL/6J and C3H/HeN mice.


METHODS
At indicated times after various doses of thoracic irradiation, the cell populations obtained by bronchoalveolar lavage of C57BL/6J mice were differentially analyzed by cytology and assessed by RNase protection (RPA) assay for levels of cytokines and related genes. The molecular responses in bronchial alveolar lavage (BAL) populations were compared with those in whole lung of C57BL/6J mice and with those of C3H/HeN mice. The former strain develops late radiation fibrosis, whereas the latter develop subacute radiation pneumonitis.


RESULTS
In C57BL/6J mice, a decrease in the total number of BAL cells was found 1 week after 6, 12, or 20 Gy thoracic irradiation with a subsequent dose-dependent increase up to 6 months. After 12 and 20 Gy, large, foamy macrophages and multinucleated cells became evident in BAL at 3 weeks, only to disappear at 4 months and reappear at 6 months. This biphasic response was mirrored by changes expression of mRNA for proinflammatory cytokines and the Mac-1 macrophage-associated antigen. As with BAL, whole lung tissue also showed biphasic cytokine and Mac-1 mRNA responses, but there were striking temporal differences between the two compartments, with changes in whole lung tissue correlating better than BAL with the onset of fibrosis in this strain. The radiation-induced proinflammatory mRNA responses had strain-dependent and strain-independent components. Thoracic irradiation of C3H/HeN induced similar increases in tumor necrosis factor (TNF)-alpha, interleukin (IL)-1alpha/beta, and interferon (IFN)-gamma mRNA expression in lung as it did in C57BL/6J mice during the "presymptom" phase at 1-2 months. However, immediately preceding and during the pneumonitic time period at 3-4 months, TNF-alpha and IL-1alpha/beta mRNAs were highly upregulated in C3H/HeN mice, which develop pneumonitis, but not in C57BL/6J mice, which do not. At the onset of radiation fibrosis in C57BL/6J mice (5-6 months), irradiated lungs had increased levels of IL-1alpha/beta and IFN-gamma mRNA expression, but the TNF-alpha response was, notably, still muted.


CONCLUSIONS
The major molecular and cellular events in lungs of C57BL/6J and C3H/HeN mice, which develop late fibrosis and subacute pneumonitis after thoracic irradiation respectively, take place within the interstitium and are not reflected within BAL populations. The initial proinflammatory responses are similar in the two strains, but later responses reflect the latent time to lesion development. TNF-alpha expression at 3-4 months may be important in radiation-induced pneumonitis, and its downregulation is important in avoiding this radiation-induced complication.
Chiang
Chi-Shiun
CS
Department of Atomic Science, National Tsing Hua University, Taiwan.
Liu
Wei-Chung
WC
Jung
Shih-Ming
SM
Chen
Fang-Hsin
FH
Wu
Chi-Rong
CR
McBride
William H
WH
Lee
Chung-Chi
CC
Hong
Ji-Hong
JH
D000818:Animals; D018893:Bronchoalveolar Lavage; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D002452:Cell Count; D016207:Cytokines / Q000378:metabolism*; D008168:Lung / Q000378:metabolism / Q000528:radiation effects*; D016177:Macrophage-1 Antigen / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000528:radiation effects*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000378:metabolism; D011829:Radiation Dosage; D017564:Radiation Pneumonitis / Q000209:etiology* / Q000378:metabolism; D013045:Species Specificity; D013909:Thorax; D013997:Time Factors
D016207:Cytokines; D016177:Macrophage-1 Antigen; D012333:RNA, Messenger