HP and irritable bowel syndrome: The immunomodulatory hemoglobin-binding protein haptoglobin (HP) gene harbors a common polymorphism with two different alleles: HP1 and HP2; in human, allele HP2 (genotype HP22) has been shown to be overrepresented in different immune diseases, as well as in patients with IBD (ulcerative colitis—UC and Crohn’s disease—CD) [11,12,13,14], type-1-diabetes (T1D) and insulin resistance [15], irritable bowel syndrome (IBS) [16], necrotizing enterocolitis [17], and nonceliac gluten sensitivity [18], compared to healthy controls [19].