Anti-tumor necrosis factor α therapy associates to type 17 helper T lymphocytes immunological shift and significant microbial changes in dextran sodium sulphate colitis

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 5 and 12 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.