CA IV may be target antigen in autoimmune pancreatitis

Japanese researchers have uncovered a serum antibody that may prove to be a marker for disease affecting multiple exocrine glands—like autoimmune pancreatitis (AIP) and Sjögren’s syndrome (SS). The target antigen—carbonic anhydrase isozyme IV (CA IV)—is commonly found in exocrine gland epithelia.

The antibody was significantly more common among patients with definite (27%) or probable (43%) AIP and SS (45%) than among those with pancreatic cancer (14%) or alcoholic chronic pancreatitis (13%), when compared with healthy controls in an ELISA screen with truncated recombinant CA IV antigen. The same trend occurred in a parallel screen with a synthetic peptide of CA IV. Reactivity of in vivo CA IV—the entire protein in its native configuration—remains to be confirmed, as does its potential role in pathogenesis.

Fifteen patients had definite AIP and 14 probable AIP; 15 had alcoholic chronic pancreatitis and 14 pancreatic cancer; 20 patients had SS; and there were 30 controls.

AIP shows lesions in other organs that are redolent of other diseases—SS in salivary glands; extrahepatic sclerosing cholangitis; and, occasionally, ulcerative colitis—with epithelial inflammation as the common feature. This suggests an autoimmune reaction to a common antigen. Previous studies have shown serum antibodies to CA I and II in idiopathic chronic pancreatitis and SS, though these do not cross react. This study looked for another cross reacting target antigen—and checked for serum antibody to CAs IV, IX, and XII expressed in pancreatic duct epithelia.