FOXP3 and ankylosing spondylitis: Consistent with this hypothesis, in patients with ankylosing spondylitis, peripheral blood Treg was characterized by low Foxp3 expression, little STAT5 phosphorylation upon IL-2 stimulation, and more extensive methylation in the CNS2 region of the FOXP3 gene, confirming that functional defects of Treg are present in SpA [15].