Mucosal Immune Environment in Colonic Carcinogenesis: T-Cell Activation in Ulcerative Colitis and Dysplasia

Background In patients with ulcerative colitis (UC) the cumulative rate of dysplasia is at least 25% but the cumulative risk of colon cancer is approximately 8% twenty years after the diagnosis. The inconsistency between dysplasia rate and incidence of cancer suggests the presence of immunosurveillance mechanisms that can activate T lymphocytes against dysplastic antigens. We recently demonstrated a CD80 up-regulation in UC and dysplasia. The aim of our study was to analyse the activation of T lymphocyte CD8+ (CTL) in the colonic mucosa at the different stages of UC-related and non inflammatory carcinogenesis. Patients and methods Five groups of patients affected by UC (10 pts), UC with colonic dysplasia (7 pts), colonic adenoma (7 pts), UC and cancer (5 pts), sporadic colonic cancer (10 pts) and a group of healthy control (10 pts) were enrolled in our study. Mucosal CD8beta and CD69 (markers of CTL activation) as well as CD80 and CD86 (co-stimulatory molecules) mRNA levels were quantified with Real Time PCR. Mucosal expression of CD80, CD86, CD3, CD20, CD68 and p53 was analysed by immunohistochemistry. Mucosal levels of IL- 1β, IL-2 and IFN-gamma were measured with immunometric assays. Non-parametric Krus- kal-Wallis ANOVA, Mann-Whitney U test and Kendall's tau correlation test were used. Results In the different steps of UC-related carcinogenesis CD8beta expression resulted similar while in non inflammatory carcinogenesis it resulted lower at the invasive cancer stage (p=0.01). CD8beta expression correlated with CD80 and CD86 mRNA expression (tau=0.47, p<0.01, tau=0.38, p<0.01, respectively). CD69 mRNA expression was higher in patients with UC and dysplasia than in patients with UC and in those with UC and cancer (p=0.05 and p=0.04, respectively). This difference was not evident in the non inflammatory carcinogenesis (p=0.47). In these patients, at each step of the carcinogenesis, the expression of CD69 was lower in patients with UC, UC and dysplasia and UC and cancer (p=0.01, p<0.01 and p=0.02, respectively). CD69 expression directly correlated with CD80 mRNA and protein expression (tau=0.53, p<0.01, tau=0.30, p<0.01, respectively). Conclusion Our study showed that, in UC, mucosa infiltrating T-cell CD8beta+ are equally distributed along the carcinogenesis pathway but their activation state is significantly enhanced in the dysplastic colonic tissue. Moreover, this activation was strictly correlated with CD80 expression sug- gesting the effectiveness of this immunosurveillance mechanism in UC. On the contrary, in non inflammatory carcinogenesis CTL seemed reduced in invasive cancer. Furthermore, neither CD80 up-regulation nor consequent CTL activation were observed suggesting that the lack of CD80 expression may be the cause of the progression of dysplastic adenoma once occurred.