Anti-Ro/SSA and anti-La/SSB autoantibodies in the tear fluid of patients with Sjögren's syndrome

Sjögren's syndrome (SS) is considered to be the second most common disorder among the group of chronic systemic rheumatic diseases, exceeded only by rheumatoid arthritis. Exocrine glands are the principal target organs, but several non-exocrine organs may be affected as well. The immunopathological lesion of SS is characterised by mononuclear cell infiltrates around ductal and acinar epithelial cells of lacrimal and salivary glands, fibrosis, and gradual destruction of tissue architecture leading to severe dryness of eyes and mouth.

Autoantibodies to nuclear antigens occur in patients with multisystem autoimmune disease such as systemic lupus erythematosus, rheumatoid arthritis, and SS. Although heterogeneous, there are two major groups-autoantibodies to DNA and autoantibodies to non-DNA antigens-the latter including antinuclear antibodies to the soluble or "extractable nuclear antigens". Extractable nuclear antigens are ribonucleoproteins (RNPs) consisting of small ribonucleic acid (RNA) molecules attached to non-histone proteins and have three main categories: the U group comprising U1-U6 small nuclear RNAs, the Ro group and the La group. The Ro/SSA antigen is a small nucleocytoplasmic RNA protein complex. It consists of a 60 kDa protein which is associated with one of four human cytoplasmic RNAs (hY1, hY3, hY4, hY5). ^{1- 3} Antibodies to a 52-kDa protein (anti-52-kDa Ro) are found in some sera with anti-60-kd Ro ⁴ and association of this protein to the Ro RNP particle (60-kDa Ro plus hY RNA) remains a subject of controversy. ^{5, 6} The functions of 60-kDa Ro and 52-kDa Ro are not completely known, although 60-kDa Ro may be involved in the ribosomal RNA discard pathway. ⁷ The La/SSB antigen consists of a 48-kDa protein ⁸ and serves as a termination factor for RNA polymerase III. ^{9, 10}

Presence of anti-Ro/SSA or anti-La/SSB autoantibodies is one of the classification criteria suggested by the European Community Study Group on diagnostic criteria for SS. ¹¹ Anti-Ro/SSA antibodies are present in sera of 50-70% of SS patients, while anti-La/SSB antibodies, which are more specific for SS can be detected 45-60%. ¹²

Anti-Ro/SSA and anti-La/SSB antibodies have been demonstrated previously in the saliva of SS patients. ^{13- 15} In addition, anti-Ro/SSA and anti-La/SSB antibody producing cells were found in the labial salivary glands of SS patients. ^{16, 17} However, the presence of these autoantibodies has not been studied in...