The textbook "Regulatory T Cells and Interleukin-10" provides a comprehensive analysis of the role of regulatory T cells and Interleukin-10 (IL-10) in the context of Mycobacterium tuberculosis, a pathogen that infects one-third of the global population and causes nearly 2 million deaths annually. Despite extensive research, the understanding of the mechanisms leading to the development of active tuberculosis remains incomplete. The book examines how regulatory T cells modulate the host's immune response and the role IL-10 plays in this process. It is outlined that in certain situations, the regulation by regulatory T cells can be excessive, hindering protective immune responses, while in other cases, this control is insufficient to prevent immunopathological reactions. The study analyzes the percentage distribution of CD4+CD25+ regulatory T cells as well as the mRNA expression of IL-10 in the peripheral blood of patients with active pulmonary tuberculosis to assess their possible role in the immunopathogenesis of tuberculosis.