HNF4G and selective IgA deficiency disease: These CLAs play a role in modulating a specific subset of CD4+ intraepithelial lymphocytes in the small intestine by influencing the transcription factor HNF4γ.421 IgA plays an important role in mucosal biology, and the relatively mild symptoms of most patients with selective IgA deficiency (SIgAD) have been a clinical challenge.