Expression of major histocompatibility antigens in human chronic pancreatitis.

T-lymphocytic infiltration of the exocrine pancreas and liver in patients with chronic pancreatitis has suggested that cell mediated immune mechanisms may play a part in the pathogenesis of this disease. As expression of major histocompatibility (MHC) antigens is a prerequisite for organ specific autoimmunity, the expression of HLA class I (beta 2-microglobulin) and class II (HLA-DR) determinants have been analysed, together with the presence of T-lymphocytes, in 93 patients (64 men and 29 women, mean age 40.6 years) having an operation for chronic pancreatitis. Ethanol (63 patients), recurrent acute pancreatitis (12), congenital lesions (2), and unknown (16) were suggested to be the causes of the disease. Immunohistochemical staining of formalin fixed and paraffin wax embedded tissue sections used conventional immunohistochemical techniques with specific anti-serum samples. No MHC expression was identified in 10 histologically normal pancreatic control specimens or in four cases of chronic pancreatitis secondary to obstruction by neuroendocrine tumours within the head of the pancreas. beta 2-microglobulin expression by pancreatic exocrine epithelial cells was seen in 76 chronic pancreatitis specimens (82%) while HLA-DR was present in 61 (66%). Simultaneous expression of both class I and II determinants was seen in 53 (57%) of cases. MHC determinant expression was not found in 10 cases (11%) of chronic pancreatitis. In the positive specimens, expression was confined to ductal and ductular (interlobular and intralobular) epithelium with no staining of acinar cells. Staining was not related to the suspected cause of the disease or age. T-lymphocytes were more prominent in chronic pancreatitis mean (SEM) (131 (15) cells per high powered field) than controls (5 (1), p < 0.01). Aberrant MHC expression by exocrine pancreatic epithelial cells occurring in the presence of an appreciable T-cell infiltration confirmed that the appropriate cellular conditions were present for cell mediated cytotoxicity to contribute to the pathogenesis of chronic pancreatitis.