S1698 High Sero-Reactivity to Food Antigens Correlates with Disease Severity in Crohn's Disease, But Not in Ulcerative Colitis Patients

Abstract

IFN-γ plays an important role in the generation and perpetuation of mucosal inflammation in IBD. TL1A, a TNF superfamily member, synergizes with IL-12 and IL-18 to augment IFN-γ production in human T cells. Enhanced TL1A expression is detected in IBD with a strong TL1A SNP association reported in Crohn's disease. We have previously shown TL1A expression is induced in peripheral monocytes and in-vitro derived dendritic cells (DC). The molecular mechanisms regulating TL1A expression during DC differentiation however, remain poorly defined. The human monocytic cell line, KG-1, provides a valuable model for dendritic cell differentiation. The round non-adherent KG1 cells develop a DC-like phenotype following activation by PMA/ionomycin. These cells become loosely adherent with long cytoplasmic projections. A concomitant induction of membrane TL1A and mRNA is observed with mRNA expression being detectable within 2 hours and peaking at 8 hours following stimulation. A strikingly similar kinetics of TL1A expression was likewise noted following PMA/ionomycin stimulation of peripheral monocytes. Further DC maturation of KG-1 cells following treatment with LPS results in additional enhancement of TL1A expression. Transient transfection of KG-1 with TL1A promoter-constructs up to 1.5 kb in length reveals up to 90-fold enhanced expression compared to cells transfected with the promoterless vector. EMSA analysis demonstrates PMA/ionomycin mediated upregulation of nucleo-protein binding to a putative TL1A NFκB binding site. Binding is competed by excess unlabeled wt TL1A NFκB, but not mutant oligonucleotide and is likewise attenuated following proteasomal inhibition by MG132. Our data suggests in the human monocytic KG-1 cell line, differentiation of immature cells towards a mature DC phenotype is associated with functional upregulation of surface TL1A expression and binding of NFκB to the TL1A promoter. These studies provide a molecular basis for future studies which may help elucidate the mechanism modulating TL1A expression during DC maturation.