[CD4+CD25+Foxp3+ T lymphocytes: naturally occuring regulatory T cells].

The mechanism that plays an essential role in immunosuppression and regulation is the presence of naturally occurring regulatory T cells (Tregs), which comprise 5-10% of peripheral CD4+ lymphocytes. They are characterized by the constant and high expression of the α subunit of IL-2 receptor (CD25), which makes them different from conventional, CD4+ and CD8+ lymphocytes, which express this molecule at lower level only during the activation state. The function of regulatory T cells is to inhibit proliferation as well as cytokine production by effector CD4+CD25- lymphocytes. They are also able to suppress CD8+ T cells, monocytes, NK cells, dendritic cells and B cells. The transcription factor Foxp3 is the key regulatory gene for the development and function of regulatory T lymphocytes. Its expression is limited to CD4+CD25high T cells at both mRNA and protein levels. Foxp3 is a specific indicator of suppressive activity of Tregs and it acts as repressor as well as activator of transcription.