The regulation and function of integrin alphaE (CD103) in human dendritic cells

Abstract

Retinoic acid (RA) is a master regulator of cellular signaling and function as well as an important mediator of immune development and maintenance. CD103 is a marker that is used to distinguish functional subsets of mucosal DCs. Despite the use of CD103 as a DC marker, the RA-induced pathway leading to CD103 expression is yet unknown. In addition, the function of DC CD103 has not been fully elucidated. In this dissertation research, we evaluated the regulation of CD103 expression on human DCs and investigated the function of DC CD103. We first found that CD103 expression is driven by RA and that CD103 is found in intracellular pockets in human DCs. However, the RA-induced increase of CD103 was abrogated upon stimulation of DCs with TLR ligands. To elucidate the RA-induced pathway of CD103 expression, we established the dependence on p38 MAPK signaling and NFAT through the use of specific inhibitors. Studies with RARalpha siRNA and the use of RAR-specific agonists show that CD103 expression is dependent on RARalpha signaling. To investigate further the intracellular CD103 expression, we demonstrated that CD103 was co-localized with endosomal markers and was actively internalized over time in DCs, suggesting CD103 undergoes endosomal recycling. Based upon imaging of gastric tissue showing CD103^+ DCs are most often within the gastric epithelial layer, we sought to understand the role of CD103 in DC adhesion. We investigated whether CD103 is involved in adhesion of DCs to the epithelium by co-culturing the DCs with HT-29 cells, which express E-cadherin on the entire cell surface. Interestingly, we found that CD103 was not a main driver of DC-epithelial adhesion, but that DC binding to the gastrointestinal epithelium was mediated by the interactions between DC E-cadherin and E-cadherin on the HT-29 cells. In summary, this research has contributed to the understanding of CD103 expression and function on human DCs. CD103 plays a minor role in the adhesion of DCs to the gastrointestinal mucosa, despite CD103^+ DCs close proximity to the gastric epithelium. RA drives the expression of CD103 on DCs mediated through RARalpha and p38 MAPK signaling and NFAT.