HLA-DPA1 and inflammatory bowel disease: As an additional example, HLA-DPB1*02:01, HLA-DPB1*04:01, and HLA-DPB1*05:01 represent the alleles at the HLA-DPB1 locus, where the first two are positively correlated with HLA-DPA1*01:03, while the latter is negatively correlated with HLA-DPA1*01:03, which is the protective factor for IBD [30] (Figure 3).