The subpopulation of CD4+ T lymphocytes that co-express the transcription factor Foxp3
plays a unique role as regulatory T lymphocytes (Tregs) that modulate many aspects of the
immune response. Multiple mechanisms have been proposed for the suppressor function of
CD4+ Foxp3+ T cells based on in vitro studies, but much less is known about how Tregs
suppress immune responses in vivo. Both polyclonal Tregs and antigen-specific Tregs are
capable of exerting potent suppressive effects in vivo, and it is likely that they mediate their …