Could the IgA isotype provide additional information in systemic sclerosis patients? A retrospective study entailing IgA isotyping in a Mediterranean systemic sclerosis cohort.

Objectives: Anti-CENP-B (ACA), anti-topoisomerase I (ATA) and anti-RNA polymerase III (RP3) autoantibodies are included in the 2013 SSc-ACR/EULAR classification criteria. The detection of additional autoantibodies is of interest when those are negative. Additionally, we wonder if the IgA isotype might play a role in SSc. The aims of the study were to assess the prevalence of ACA, ATA, RP3, and Ro52 autoantibodies of IgG and IgA isotype and to describe their association with clinical manifestations in a cohort of patients with SSc.

Methods: Samples from 97 patients with SSc fulfilling the 2013 ACR/EULAR classification criteria, and 50 blood donors were included and tested for IgA and IgG isotypes of ACA, ATA, RP3, and Ro52 by FEIA.

Results: The prevalence of IgG+IgA isotypes for the same specificity was 62.5%, 82.6%, 80.0%, 36.8%, for ACA, ATA, RP3 and Ro52, respectively. Isolated IgG was present in 35.4%, 13.0%, 20.0% and 42.1% of patients for ACA, ATA, RP3 and Ro52, respectively. Only six patients were isolated IgA for a unique specificity. Clinically, ILD tended to be associated with ATA-IgG and ATA-IgG+IgA, telangiectasias with ACA-IgG+IgA and arthritis with ACA-IgA. Indeed, digital ulcers were more frequent in ATA-IgG patients.

Conclusions: Most of the patients presented ACA, ATA, or RP3 autoantibodies of IgA isotype in addition to IgG. Regarding clinical relevance, Ro52-IgG+IgA and ACA-IgG had a tendency towards sineSSc phenotype, while ACA-IgG+IgA to lcSSc phenotype. Thus, if confirmed, the determination of ACA-IgA could provide a tool to stratify patients according to the cutaneous phenotype.