Clinical and serological study of 26 patients with anti-SL (Ki) autoantibodies

Background

Anti-SL (Ki) antibody was described in 1981 in patients affected by systemic lupus erythematosus (SLE) and sicca symptoms.

Objective

To evaluate clinical and serological profile associated with anti-SL antibodies

Methods

Twenty-six consecutive sera with anti-Sl antibodies, selected from our laboratory routine ENA detection, were studied. All sera were analyzed by counter immunoelectrophoresis (CIE) for anti-ENA detection, using rabbit thymus and human spleen extract as substrates. ANA (by IFI assay on HEp-2 cells), anti-dsDNA (by Farr assay), anti-ENA, anticardiolipin (aCL) and anti-beta2GPI (by ELISA) were detected at disease onset and during follow up. The patients (20 female and 6 male) had a mean age at onset of 39.4 years (SD: 18.3 years) and a mean follow-up of 10.7 years (SD: 7.3 years).

Results

All the patients were affected by autoimmune rheumatic diseases, but one with HCV-related cryoglobulinemia. SLE and primary Sjögren Syndrome (pSS) were the most frequent diagnoses achieved (in 13 and in 6 cases, respectively). Main clinical features were represented by skin involvement (65%), Raynaud's phenomenon (38%), xerophtalmia (54%), xerostomia (34%) and serositis (15%). Nevertheless, severe manifestations of disease were frequently observed: CNS involvement in three (11.5%) and renal disease in four cases (15%), while one patient with SLE had primary pulmonary hypertension. No cases of hemolytic anemia or severe cytopenia were recorded. ANA positivity was observed in all the sera. Anti-SL antibodies were detected as isolated antibody specificity in only five patients, while nine sera showed reactivity to anti-SL plus one antinuclear specificity (5 anti-dsDNA, 2 anti-Ro, one anti-RNP, one anti-Sm). Ten patients had anti-SL antibodies associated with two other ANA specificities: in five cases, anti-Ro and anti-dsDNA; in three, anti-Ro and anti-La; in two cases, anti-Sm and anti-dsDNA. Two patients showed multiple antinuclear specificities (anti-SL with anti-Ro, anti-La and anti-dsDNA in one case and anti-SL with anti-Ro, anti-Ku and anti-dsDNA in another). Anti-cardiolipin and anti-beta2GPI were detected in seven and four patients, respectively.

Conclusion

Anti-SL antibodies identify a group of patients mainly affected by SLE and pSS, presenting in approximately one third of patients a severe disease with pulmonary, CNS or kidney involvement. Twenty-one patients with anti-SL (81%) have multiple antinuclear specificities.