P140 IgG Autoantibodies with Increased Affinity for Epithelial Cells in Severe Systemic Sclerosis

Abstract

Abstract Background/Aims In health IgG immunoglobulins form a network through interaction with cell surface proteins and controlled by regulatory cells, whereas in autoimmune diseases IgG responses become skewed towards higher affinity and potentially damaging responses against self-antigens. Moreover, recent studies have demonstrated activation of the epithelial layer of skin in systemic sclerosis (SSc), implicating keratinocytes as a target of the autoimmune process. We investigated the presence of plasma IgG autoantibodies directed against keratinocytes and sought correlation with clinical parameters in well-characterized patients. Methods Diffuse SSc (dcSSc), limited SSc (lcSSc) and healthy control (HC) plasma samples (each n = 30), were assayed in an anti-epithelial cell antibody assay (AEpCA), using fixed keratinocytes to evaluate binding of IgG . Clinical characteristics of patients with positive versus negative AEpCA were compared. The capacity for SSc IgG to activate epithelial cells was assessed using keratinocytes in vitro. Results Preliminary serial dilution assay of SSc and HC plasma (n = 10) showed enhanced affinity of SSc IgG for keratinocytes (ANOVA p < 0.001 for overall effect SSc vs HC IgG p < 0.0048 for dose effect)(Figure 1A). Dilution of 1/80 gave optimal differential binding in the AEpCA assay (corrected p < 0.027 for SSc vs HC at 1/80). Further HC, dcSSc, and lcSSc plasma samples (each n = 30) were screened, demonstrating increased AEpCA titre in SSc (Figure 1B) (Kruskall-Wallace test p < 0.014 for lcSSc vs HC, p < 0.041 for dcSSc vs HC). SSc patients with positive AEpCA had higher skin scores (mRSS) (AEPCA neg 5(0-24); AEpCA pos 9(0-40) p < 0.0032), higher frequency of ATA antibody (AEpCA neg ATA pos 6/30; AEpCA pos ATA pos 13/30, chi squared p = 0.052) more interstitial lung disease (AEPCA neg 7/30, AEpCA pos 13/30, p NS)(Figure 1C) and trend towards higher use of immunosuppression. SSc but not HC IgG activated keratinocytes in vitro, triggering IL-1α release. Conclusion In this study, we have shown evidence of IgG autoantibodies with increased affinity for keratinocytes in the plasma of SSc patients. Positive testing for the AEpCA was associated with more severe skin disease and lung involvement. The perturbed IgG network in such patients could be activating through common epithelial cells antigens in the skin and lung. Disclosure C. Moezinia: None. V. Wong: None. J. Watson: None. L. Nagib: None. S. Lopez Garces: None. H. Lopez: None. G. Martin: None. S. Zhang: None. B. Ahmed Abdi: None. C. Denton: None. D. Abraham: None. R.J. Stratton: None.