Inflammatory bowel disease (IBD) is an autoimmune disease triggered by inappropriate response to antigens. Patients with IBD can be ranked roughly into two categories: ulcerative colitis (UC) and Crohn's disease (CD). An increase level of TNF-α can be observed in inflamed tissue, and also in the inflamed mucosa of patients with IBD. Biological agents that can be used for the treatment of IBD are TNF-α inhibitors, impacting intracellular signaling. They inhibit the cell cycle, accelerate apoptosis of activated cells, inhibit cytokine production, or improve the activity of regulatory T cells. Communication between immune cells and response to antigens is crucial for homeostasis in the intestinal mucosa. Lymphocytes T and their response have an important function in the pathogenesis of IBD. In our study, we focused on certain subtypes of T lymphocytes in the inflamed bowel mucosa of patients with IBD. The lymphocytes were isolated from biopsy of the intestinal mucosa of patients with IBD who received TNF-α inhibitors due to the ineffectiveness of the response to standard therapy. All samples were taken from the intestinal mucosa before and after three months of treatment. 26 patients participated, 15 of which were CD patients, and 11 were diagnosed as patients with UC. For comparison, we included 10 healthy control patiens. We used flow cytometry method to measure the ratios of lymphocytic subtypes in the research subjects. The differences between patients and control group showed in i) cytotoxic T lymphocytes expressing costimulatory molecules CD28, ii) ratio of cytotoxic T lymphocytes expressing/not expressing costimulatory molecules CD28, iii) the population of activated cytotoxic T cells, iv) activated helper T cells and v) regulatory T cells. We conclude that the cytotoxic T cells (CD8 + CD28 + and CD8 + CD28-) and their ratios are involved in the development of the disease. Patients with UC had lower frequency of cytotoxic T lymphocytes expressing CD28 molecule and residual lymphocytes T after treatment, moreover UC patients who responded to therapy had lower frequency of activated cytotoxic T cells after treatment. Activated T cells expressing IL2R receptor are more represented in non-responsive CB patients before treatment than in responsive. The feature of the IBD is also the disrupted activity of T regulatory cells, which was also confirmed in our study, as the proportion of Treg in the control group was higher than in patients with IBD before therapy.