Carboanhydrase II-autoantibodies

The isoenzyme- and species-specific carbonic anhydrase autoantibodies may inhibit the activity of the enzyme. Some of the antibodies may be directed against the catalytically active epitope of the enzyme. In patients with systemic lupus erythematosus, antibodies against carbonic anhydrase I and II were found in a higher percentage in those patients who had concomitant anti-U1-snRNP and anti-SS-A / Ro.

Along with haemoglobin, carbonic anhydrase (Ec 4.2.1.1.; Mr 29 kDa) is a major protein component of erythrocytes. The enzyme occurs in at least 6 isoforms in the organism, of which carbonic anhydrase I (low activity) and carbonic anhydrase II (high activity) occur in erythrocytes. The zinc metallo enzyme catalyzes the reversible reaction CO2 + H2O > HCO3- + H+. Hereditary carbonic anhydrase II deficiency results in a syndrome of osteoporosis, renal tubular acidosis, and cerebral calcifications.

Due to the low disease specificity, the diagnostic significance of the autoantibodies is relatively low. The assumption that they are marker antibodies for patients with mitochondrial antibody negative primary biliary cirrhosis has not been confirmed. The frequency in healthy individuals is reported to be 2 - 12 %.

Occurrence Antibodies against carbonic anhydrase are found in:

• systemic lupus erythematosus (33 %),
• systemic scleroderma (12 %)
• polymyositis (12 %)
• dermatomyositis (25 %)
• primary Sjögren's syndrome (17 %).

Furthermore in

• endometriosis (35 - 69 %)
• primary biliary cirrhosis (35 %),
• autoimmune hepatitis (30 %)
• autoimmune pancreatitis (AIP),
• immunocoagulopathy
• Diabetes mellitus type 1