IgG4 in the gut: Gastrointestinal IgG4-related disease or a new subtype of inflammatory bowel disease.

IgG4-related disease (IgG4-RD) is a chronic inflammatory condition characterized by tissue infiltration with IgG4-positive plasma cells, leading to fibrosis and organ dysfunction. While primarily affecting the pancreas, bile ducts, and salivary glands, IgG4-RD can also involve the gastrointestinal tract, raising questions about its relationship with inflammatory bowel disease (IBD). Recent studies suggest that patients with IBD may exhibit histological and serological features consistent with IgG4-RD, such as a dense lymphoplasmacytic infiltration, a storiform-type of fibrosis and a prominent IgG4 immune response. This overlap represents a diagnostic challenge, as differentiating between primary IBD and IgG4-RD involving the gut is crucial for appropriate treatment. Further research is essential to delineate the prevalence of tissue and serum IgG4 expression in patients with IBD. This approach could classify subtypes of IBD, enabling advancements in non-invasive diagnosis and monitoring as well as personalized therapies. The purpose of this review is to summarize the available evidence regarding intestinal involvement in IgG4-RD and the role of both serum and tissue IgG4 in inflammatory bowel diseases IBD.