IGHG1 and Crohn disease: Immunoglobulin genes show active IgG class-switching with IGHG1 and IGHG3 that comprise the IgG1 and IgG3 isotypes, respectively, and they were up-regulated in both the mucosa and submucosa/wall, while IGHG2 of the IgG2 isotype was selectively up-regulated in the mucosa, which suggests differences in these microenvironments that may regulate the differentiation and function of B cells in Crohn’s disease [32].