CTLA4 and colitis: We also confirm for the first time that LRBA is required for surface expression of CTLA4 by Treg cells in the lamina propria of the LI, which has not been assessed in LRBA-deficient humans and was not observed in the oscar mutants of LRBA deficiency identified as part of an ENU mutagenesis screen for colitis susceptibility loci (13).