Selective IgA 2 deficiency in a patient with small intestinal Crohn’s disease

Abstract The human IgA response is composed of two structurally different subclasses termed IgA 1 and IgA 2 . Compared to IgA 1 , IgA 2 has a shorter hinge region, which makes it more resistant to bacterial proteases. IgA 1 is produced both systemically and in mucosal surfaces, whereas IgA 2 is mostly confined to the intestines. While the overall IgA response is known to be involved in intestinal homeostasis, the specific contribution of IgA 1 and IgA 2 remains largely unknown (Chen 2020). Selective IgA deficiency (SIgAD) is the most prevalent primary immune deficiency. About half of SIgAD cases are associated with heterogeneous but generally mild clinical manifestations. Anecdotal evidence of IgA 2 deficiency is available (van Loghem 1983, Ozawa 1986, Engström 1990), however no associations with clinical manifestations have been reported. Here, we describe the occurrence of a selective IgA 2 deficiency in a patient (CD068) with small intestinal Crohn’s disease (CD). The patient had undetectable IgA 2 + cells and secreted IgA 2 antibody in both intestine and circulation. Among other features, patient CD068 presented with duodenal and ileal inflammation. To our knowledge, this is the first case of IgA 2 deficiency with a potential link to IBD, which might shed new insights into potential IgA 2 -specific functions.