Journal of Autoimmunity (1999) 13, 429–434 Article No. jaut.1999.0333, available online at http://www.idealibrary.com on Autoantibodies to La/SSB in Patients with Primary Sjo ¨ gren’s Syndrome (pSS) are Associated with Upregulation of La/SSB mRNA in Minor Salivary Gland Biopsies (MSGs) Athanasios G. Tzioufas, Ioanna Hantoumi, Mary Polihronis, Georgia Xanthou and Haralampos M. Moutsopoulos Department of Pathophysiology, Medical School, National University of Athens, Athens, Greece Received 12 March 1999 Accepted 3 September 1999 Recent studies have shown that minor salivary glands (MSGs) of patients with primary Sjo ¨gren’s syndrome (pSS) are sites of anti-La/SSB autoantibody production. The aim of this study was to investigate the expression of La/SSB mRNA in MSGs of patients with pSS. La/SSB mRNA expression was studied by in situ hybridization in six biopsies of pSS patients with anti-La/SSB antibodies, nine pSS patients without anti-La/SSB and 10 patients with non-specific sialadenitis. Oligonucleotide probes corresponding to c-DNA encoding four linear epitopes of La/SSB (bp 423–471, bp 861–909, bp 903–954 and bp 1048–1092) were utilized. cDNA encoding linear epitopes of Ro52 (bp 786–837), Ro60 (bp 654–702) and the housekeeping genes of Sm and GAPDH were used as controls. The results were expressed as percent of positive cells by image analysis. Serum levels of anti-La/SSB autoantibodies were correlated with the presence and the intensity of La/SSB mRNA labeling. All pSS patients with anti-La/SSB antibodies in their serum expressed mRNA transcripts of epitopes 301–318 aa and 349–364 aa (encoded by the cDNA probes bp 903–954 and bp 1048–1092 respectively), predominantly in acinar and mononuclear cells of MSGs. These epitopes are the major targets of anti-La/SSB antibodies. Serum levels of anti-La/SSB antibodies were correlated with the number of positively stained cells in MSGs. Two of the nine pSS patients without anti-La/SSB autoantibodies and 2/10 non-pSS patients expressed the mRNA of the La/SSB molecule. The probes of RO52 and Ro60 epitopes did not react, while mRNA encoding the housekeeping genes of Sm and GAPDH was positive in all samples. In conclusion, pSS patients with anti-La/SSB anti- bodies showed upregulation of La/SSB mRNA in acinar and mononuclear cells of MSGs. Thus, active synthesis of La/SSB in MSGs of pSS seems to play an important role in the autoimmune response of the affected tissues. © 1999 Academic Press Key words: Sjo ¨ gren’s syndrome, La/SSB, B cell epitopes, antigen presentation, La/SSBmRNA Introduction Autoantibodies to the ribonucleoprotein complex La/SSB are primarily found in sera from patients with pSS. The La protein, which is the target of the autoantibodies, has a molecular weight of approximately 48 Kda and it is transiently associated with almost all RNA polymerase III transcripts as well as a diverse spectrum of leader RNAs of different viruses. Thus, La/SSB is actively involved in transcription termination of RNA polymerase III transcripts [1]. A large body of knowledge mounted over the past several years suggests that the autoantibody response is antigen-driven, since B cell epitope mapping studies of La polypeptides indicate the autoimmune response is polyclonal [2], disease-specific [3], class switched, involving species specific epitopes [4], capable of inducing experimental intra- and intermolecular epitope spreading [5]. Despite the fact that the origin of anti-La/SSB autoantibodies is presently unclear, the site of their production seems to be located in the affected exocrine glands. Indeed, B cells in the immu- nopathologic lesion of SS are activated [6]; anti-La/ SSB antibodies have been demonstrated in the Correspondence to: Dr A. G. Tzioufas, Department of Pathophysi- ology, Medical School, 75 M. Asias Street, 11527 Athens, Greece. Tel: +301 7771095, Fax: +301 7703876. 429 0896–8411/99/080429+06 $30.00/0 © 1999 Academic Press