Acute and persisting Th2-like immune response after fractionated colorectal γ-irradiation

AIM： To investigate if an immune imbalance may account for the development and progression of chronic radiation enteritis. We analyzed the Th1/Th2 immune response profile early and 6 mo after fractionated colorectal irradiation. METHODS： A rat model of fractionated colorectal γ-irradiation （4-Gy fractions, 3 fractions per week） was designed to investigate the effects of cumulative dose on inflammatory mediators （cytokines and chemo- kines） and immune response （Th1/Th2 profile and immunosuppressive mediator IL-10） during acute （early） response and 6 mo after the end of fractionated irradiation （chronic response）. Analyses were performed 1 d after the cumulative doses of 16 Gy and 36 Gy and 1 d, 3 d, and 26 wk after the cumulative dose of 52 Gy. RESULTS： Without causing histological damage, fractionated radiation induced elevated expression of IL-1β, TNFα, MCP-1, and iNOS in distal colonic mucosa during the early post-irradiation phase. At that time, a Th2 profile was confirmed by expression of both the Th2- specific transcription factor GATA-3 and the chemokine receptor CCR4 and by suppression of the Thl cytokine IFNγ/IP-10 throughout the irradiation protocol. After 6 mo, despite the 2-fold reduction of iNOS and MCP-1 levels, the Th2 profile persisted, as shown by a 50% reduction in the expression of the Thl transcription factor T-bet, the chemokine receptor CCXCR3, and the IFNγ/ STAT1 pathway. At the same time-point, the immunosuppressive IL-10/STAT3 pathway, known to regulate the Th1/Th2 balance, was expressed, in irradiated rats, at approximately half its level as compared to controls.This suppression was associated with an overexpression of SOCS3, which inhibits the feedback of the Thl polarization and regulates IL-10 production. CONCLUSION： Colorectal irradiation induces Th2 polarization, defective IL-10/STAT3 pathway activation and SOCS3 overexpression. These changes, in turn, maintain a immunological imbalance that persists in the long term.

Caffeic acid phenethyl ester modifies the Thl/Th2 balance in ileal mucosa afterγ-irradiation in the rat by modulating the cytokine pattern

AIM： To pharmacologically modulate Th polarization in the ileum exposed to ionizing radiation by using the immuno-modulatory/apoptotic properties of Caffeic Acid Phenethyl Ester （CAPE）. METHODS： Rats received CAPE （30 mg/kg） treatment ip 15 min prior to intestinal 10 Gy γ-irradiation and once a day for a 6 d period alter irradiation. Expression of genes implicated in Th differentiation in ileal mucosa （IL-23/IL-12Rβ2）, Th cytokine responses （IFN-γ, IL-2, IL-4, IL-13）, Th migratory behaviour （CXCR3, CCR5, CCR4）, Th signalling suppressors （SOCS1, SOCS3）, transcription factor （T-Bet, GATA-3） and apoptosis （FasL/Fas, TNF/TNFR, XIAP, Bax, caspase-3） was analyzed by RT-PCR 6 h and 7 d post-irradiation. CD4^＋ and TUNEL positive cells were visualized by immunostaining. RESULTS： The expression of Thl-related cytokine/ chemokine receptors （IFN-γ, IL-2, CXCR3, CCR5） was repressed at 7 d post-irradiation while Th2 cell cytokine/ chemokines （IL-4, IL-13, CCR4） were not repressed or even upregulated. The irradiation-induced Th2 profile was confirmed by the upregulation of both Th2-specific transcription factor GATA-3 and SOCS3. Although an apoptosis event occurred 6 h alter 10 Gy of intestinal γ-irradiation, apoptotic mediator analysis showed a tendency to apoptotic resistance 7 d post-irradiation. CAPE amplified apoptotic events at 6h and normalized Bax/FasL expressions at 7 d. CONCLUSION： CAPE prevented the ileal Th2 immune response by modulating the irradiation-influenced cytokine environment and apoptosis.

Expression of matrix metalloproteinases and tissue inhibitor metalloproteinases increases in X-irradiated rat ileum despite the disappearance of CD8a T cells

AIM： To investigate their expression and activity in the rat ileum after exposure to ionizing radiation along with that of the cellular effectors and molecular mediators involved in the regulation of MMPs. METHODS： Rats were exposed to a single 10-Gy dose of X-rays delivered to the abdomen. A combination of methods, such as zymography, immunohistochemistry and real time reverse transcriptase-polymerase chain reaction, were used to localize and quantify MMPs and the molecules involved in MMP activating and inhibitory pathways （plasmin/ plasminogen, TIMPs）, CD^8＋, as well as inflammatory （interleukin （IL）-1β, IL-8, tumor necrosis factor-s, TNF-α） and fibrogenic mediators （transforming growth factor- β1-3） within ileal tissue at 1, 3, and 7 d after irradiation. RESULTS： A marked increase in MMP-2 and -14 mRNA and protein levels associated with an increased activity of MMP-2 was observed in irradiated ileal tissue. MMP-2 and -14 expression was mainly observed in inflammatory, epithelial, and mesenchymal cells, whereas a slight increase in MMP-3 expression was detected in the few infiltrating macrophages at d i after irradiation. Conversely, MMP-1, -7, and -9 mRNA levels were not found to be affected by abdominal irradiation. Irradiation was found to induce disappearance of CD^8＋ cells. Furthermore, we have observed that TNF-α and IL-1β protein levels increased 6 h after irradiation, whereas those of IL-8 only increased after 3 d and was concomitant with neutrophil infiltration. In addition, the expressions of molecules involved in MMP activating and inhibitory pathways （urokinase-type plasminogen activator andtissue-type plasminogen activator; TIMP-1, TIMP-2, and plasminogen activator-inhibitor-i） were found to be increased after abdominal irradiation. CONCLUSION： This study showed that abdominal irradiation induces an acute remodeling of the ileum associated with an increased expression of MMPs and TIMPs that do not involve CD^8＋ T cells but involve mesenchymal and epithelial cells, although to a lesser extent, and probably even soluble inflammatory and fibrogenic mediators.