BACKGROUND: Anti-tumor necrosis factor α (TNFα) represents the best therapeutic option to induce mucosal healing and clinical remission in patients with moderate-severe ulcerative colitis. On the other side gut microbiota plays a crucial role in pathogenesis of ulcerative colitis but few information exists on how microbiota changes following anti-TNFα therapy and on microbiota role in mucosal healing.
AIM: To elucidate whether gut microbiota and immune system changes appear following anti TNFα therapy during dextran sulfate sodium (DSS) colitis.
METHODS: Eighty C57BL/6 mice were divided into four groups: "No DSS", "No DSS + anti-TNFα", "DSS" and "DSS + anti-TNFα". "DSS" and "DSS + anti-TNFα" were treated for 5 d with 3% DSS. At day 3, mice whithin "No DSS+anti-TNFα" and "DSS+anti-TNFα" group received 5 mg/kg of an anti-TNFα agent. Forty mice were sacrificed at day 5, forty at day 12, after one week of recovery post DSS. The severity of colitis was assessed by a clinical score (Disease Activity Index), colon length and histology. Bacteria such as Bacteroides, Clostridiaceae, Enterococcaceae and Fecalibacterium prausnitzii (F. prausnitzii) were evaluated by quantitative PCR. Type 1 helper T lymphocytes (Th1), type 17 helper T lymphocytes (Th17) and CD4+ regulatory T lymphocytes (Treg) distributions in the mesenteric lymph node (MLN) were studied by flow cytometry.
RESULTS: Bacteria associated with a healthy state (i.e., such as Bacteroides, Clostridiaceae and F. prausnitzii) decreased during colitis and increased in course of anti-TNFα treatment. Conversely, microorganisms belonging to Enterococcaceae genera, which are linked to inflammatory processes, showed an opposite trend. Furthermore, in colitic mice treated with anti-TNFα microbial changes were associated with an initial increase (day 5 of the colitis) in Treg cells and a consequent decrease (day 12 post DSS) in Th1 and Th17 frequency cells. Healthy mice treated with anti-TNFα showed the same histological, microbial and immune features of untreated colitic mice. "No DSS + anti-TNFα" group showed a lymphomononuclear infiltrate both at 5th and 12th d at hematoxylin and eosin staining, an increase of in Th1 and Th17 frequency at day 12, an increase of Enterococcaceae at day 5, a decrease of Bacteroides and Clostridiaceae at day 12.
CONCLUSION: Anti-TNFα treatment in experimental model of colitis improves disease activity but it is associated to an increase in Th17 pathway together with gut microbiota alteration.