One hypothesis is that HAEC may result from differing immune responses to microbial antigens in HD patients as has been found in patients with inflammatory bowel disease. Antibodies to the E. coli outer-membrane porin C (OmpC), the Pseudomonas fluorescens CD related protein (I2), anti CBiR1 (anti-flagellin), as well as Saccaromyces cerevisiae (ASCA) and autoantigens, perinuclear anti-neutrophil antibody (pANCA) are known to be elevated in the patients diagnosed with Crohn Disease (CD) and ulcerative colitis (UC). Established patterns of elevation of these antibodies serve as very important tools in establishing a diagnosis of IBD, as well as distinguishing patients with UC from those with CD.