Changes in Natural Foxp3⁺Treg but Not Mucosally-Imprinted CD62L^negCD38⁺Foxp3⁺Treg in the Circulation of Celiac Disease Patients

<div><p>Background</p><p>Celiac disease (CD) is an intestinal inflammation driven by gluten-reactive CD4⁺ T cells. Due to lack of selective markers it has not been determined whether defects in inducible regulatory T cell (Treg) differentiation are associated with CD. This is of importance as changes in numbers of induced Treg could be indicative of defects in mucosal tolerance development in CD. Recently, we have shown that, after encounter of retinoic acid during differentiation, circulating gut-imprinted T cells express CD62L^negCD38⁺. Using this new phenotype, we now determined whether alterations occur in the frequency of natural CD62L⁺Foxp3⁺ Treg or mucosally-imprinted CD62L^negCD38⁺Foxp3⁺ Treg in peripheral blood of CD patients. In particular, we compared pediatric CD, aiming to select for disease at onset, with adult CD.</p><p>Methods</p><p>Cell surface markers, intracellular Foxp3 and Helios were determined by flow cytometry. Foxp3 expression was also detected by immunohistochemistry in duodenal tissue of CD patients.</p><p>Results</p><p>In children, the percentages of peripheral blood CD4⁺Foxp3⁺ Treg were comparable between CD patients and healthy age-matched controls. Differentiation between natural and mucosally-imprinted Treg on the basis of CD62L and CD38 did not uncover differences in Foxp3. In adult patients on gluten-free diet and in refractory CD increased percentages of circulating natural CD62L⁺Foxp3⁺ Treg, but normal mucosally-imprinted CD62L^negCD38⁺Foxp3⁺ Treg frequencies were observed.</p><p>Conclusions</p><p>Our data exclude that significant numeric deficiency of mucosally-imprinted or natural Foxp3⁺ Treg explains exuberant effector responses in CD. Changes in natural Foxp3⁺ Treg occur in a subset of adult patients on a gluten-free diet and in refractory CD patients.</p>