For this purpose, we determined the percentage of T and B lymphocytes with the expression of selected activation markers (CD69+ and CD25+) and T lymphocytes (CD3+ and CD4+) with the intracellular expression of selected cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-17) in a group of patients with type 1 diabetes and in a control group. The gene discussed is IFNG; the disease is type 1 diabetes mellitus.