Lipopolysaccharide-activated CD4+CD25+ T regulatory cells inhibit neutrophil function and promote their apoptosis and death.

CD4+CD25+ T regulatory (Treg) cells play a central role in the suppression of immune response and prevention of autoimmune reactions. Pathogen recognition receptors expressed by immune cells, such as TLRs, may provide a critical link between the innate and adaptive immune systems. There is also evidence that TLR ligands can directly modulate the suppressive capacity of Treg cells. Here, we showed that CD4+CD25+ Treg cells affect neutrophil function and survival and that the TLR4 ligand is involved in the regulation of the cell interactions. We found that LPS-activated Treg cells inhibit reactive oxygen intermediates and cytokine production by neutrophils. Moreover, Treg cells reverse LPS-induced survival of neutrophils and promote their apoptosis and death. We also found that TCR-activated Treg cells induce the same effects on polymorphonuclear neutrophils as those achieved by TLR4 stimulation. Importantly, the suppressive potential of CD4+CD25+ Treg cells induced by LPS seems to be partially IL-10 and TGF-beta dependent, whereas anti-CD3/CD28 stimulation is rather contact dependent. Together, these observations suggest that Treg cells have the ability to directly regulate neutrophil function and life span when both types of the cells are exposed to LPS.