Autoimmune pancreatitis is best described as:

Autoimmune pancreatitis is best characterized as an IgG4-related systemic disease, which involves an immune-mediated inflammatory process affecting the pancreas and often other organs. It is marked by elevated serum IgG4 levels and tissue infiltration by IgG4-positive plasma cells. Unlike infectious or hereditary causes, this condition responds well to corticosteroid therapy, highlighting its autoimmune nature. Recognizing it as an IgG4-related disease is essential for guiding appropriate medical treatment and avoiding unnecessary surgery. This systemic involvement and immune basis distinguish it from viral, diabetic, or hereditary pancreatic diseases.

Reference: Harrison's Principles of Internal Medicine, 20th Edition.