IL15 and celiac disease: Although retinaldehyde dehydrogenase (encoded by ALDH1A2) produces the normally immunosuppressive retinoic acid, which imprints gut homing on T cells [27] and switches the pro-inflammatory Th17 to a regulatory response [28], in active celiac disease the impact appears quite the opposite whereby elevated retinoic acid and IL-15 promotes Th1/17 responses in the gut mucosa [29].