CD4 and chronic obstructive pulmonary disease: In this group of cells, Tregs are critical for maintaining immune tolerance by suppressing or downregulating the induction and proliferation of effector T cells.[34] Tregs consist of several forms, among which the best researched are those that are CD4+, CD25+, and FoxP3+ as opposed to Th17 cells.[34,35] The transcription factor Foxp3 seems to be a crucial marker because its presence and upregulated expression are required for Tregs development and function, preventing autoimmune diseases.[30] Previous studies have reported the occurrence of Tregs in various COPD materials.