Avian CD4(+)CD25(+) regulatory T cells: properties and therapeutic applications

Regulatory T cells (Tregs) are a subset of T cells that specialize in immune suppression. CD4(+)CD25(+)FoxP3(+) T cells have been characterized as Tregs and extensively studied in mammals. In the absence of a putative FoxP3 ortholog in avians, CD4(+)CD25(+) cells is characterized as Tregs in avians. Avian CD4(+)CD25(+) cells produce high amounts of IL-10, TGF-β, CTLA-4, and LAG-3 mRNA; lack IL-2 mRNA; and suppress T cell proliferation in vitro through both contact-dependent and -independent pathways. Depleting avian CD4(+)CD25(+) cells increases the proliferation of, IL-2 amount, and IFNγ mRNA amount of CD4(+)CD25(-) cells. Avian CD4(+)CD25(+) cells lose their suppressive properties immediately after inflammation and acquire supersuppressive properties once inflammation subsides. Although Treg activity could be beneficial to the host, Tregs simultaneously inhibit host immunity and cause persistent infections of certain pathogens. Therapy targeted toward alleviating Treg mediated immune suppression can improve host immunity against those persistent pathogens and benefit poultry production.