CD4+ Trm cells (CCR7-CD45RA-CD69+) were decreased in all layers of the appendix combined in children with complex compared to simple appendicitis (epithelium simple appendicitis median 44%, IQR 37-51% versus complex appendicitis median 17%, IQR 8-36%; lamina propria median 58%, IQR 47-61% versus median 15%, IQR 7-33%; muscular layer median 42%, IQR 32-50% versus median 5%, IQR 2-16%) (Figures 3A, B). This evidence concerns the gene CCR7 and appendicitis.