Purpose

Specific Aim 1: Characterize the effects of vitamin D treatment on expression of α4β7 on B cells in patients with inflammatory bowel disease (IBD). Specific Aim 2: Determine the effects of vitamin D treatment on fecal immunoglobulins, percentage of Ig-coated gut bacteria, gut microbiome composition (global and bound by immunoglobulins) in patients with IBD and the association of these parameters with change in α4β7+ B cells . Specific Aim 3: Compare BCR repertoire (BCR clonotypes, immunoglobulin heavy chain gene (IGHV), and isotype usage) between α4β7+ and α4β7- B cells in patients with IBD and identify α4β7+ BCR clonotypes associated with Ig-bound gut bacteria .