CD28 and appendicitis: In the CD8+ T cell compartment, a trend towards a reduced CD28 expression on CD8+ Tem cells was observed in all layers of the appendix combined of children with complex compared to simple appendicitis (epithelium simple appendicitis median 81%, IQR 77-83% versus complex appendicitis median 71%, IQR 51-74%; lamina propria median 77%, IQR 66-77% versus median 66%, IQR 58-72%; muscular layer median 74%, IQR 64-78% versus median 52%, IQR 49-68%) (Figures 2D, F).