Carbonic Anhydrase VI (CA VI) IgA Antibodies

Laboratory assay overview

Sjogren's syndrome (SS) is a systemic autoimmune disease in which loss of salivary gland and lachrymal gland function is associated with hypergammaglobulinemia, autoantibody production, mild kidney and lung disease and eventually lymphoma. SS involves dry eyes and dry mouth without systemic features that may be either primary or secondary to another autoimmune disease, such as SLE. Patients with SS and picked up at a late stage in their disease, after the salivary glands and lachrymal glands are already destroyed, because they are asymptomatic until that time. At this point, only symptomatic treatment can be offered for abnormal lachrymal and salivary gland function. The diagnosis for SS is currently at a crossroad with the American College of Rheumatology providing which requires characteristic autoantibodies (SS-A/SS-B) or minor salivary gland biopsy. Since lip biopsies are not frequently performed in clinical practice, there is increased emphasis placed on autoantibodies in diagnosis. The current Ro and La antibodies can delay the diagnosis by over 6 years.Recently novel antibodies identified to salivary gland protein 1 (SP-1), carbonic anhydrase 6 (CA6) and parotid secretory protein (PSP) using western blot methodology. Further studies have shown that the isotype differentiation of the markers adds to the sensitivity of diagnosis of SS. These autoantibodies occurred earlier in the course of the disease than antibodies to Ro or La. In addition antibodies to SP-1, CA-6 and PSP were found in patients meeting the criteria for SS who lacked antibodies to Ro or La. Furthermore, in patients with idiopathic xerostomia and xerophthalmia for less than 2 years, 76% had antibodies to SP-1 and/or CA6 while only 31% had antibodies to Ro or La. Antibodies to different isotypes (IgG, IgM & IgA of SP-1, CA6 and PSP are useful markers for identifying patients with SS at early stages of the disease or those that lack antibodies to either Ro or La.