Pos0993 Elevated Intracellular Ifn Signaling by T and B Cells but Unaltered B Cell Distribution Is a Characteristic of Anti-Ssa Positive Asymptomatic Women at-Risk for Congenital Heart Block

Background: The presence of autoantibody Ro/SSA and a type I interferon (IFN) signature are risk factors for the development of autoimmune congenital heart block (CHB) (1,2). While the effects of anti-SSA antibodies have been extensively documented in women diagnosed with Sjögren's disease (pSS) or systemic lupus erythematosus (SLE), the implications for asymptomatic women who harbor these antibodies (at-risk) remain less understood. Thus, there exists a necessity for a deeper understanding of potential IFN consequences and B cell abnormalities among those at-risk women to stratify pregnancy monitoring and evaluate treatment strategies. Objectives: To characterize the IFN signaling pathway on peripheral T and B cells in asymptomatic SSA+ women at-risk for CHB in comparison to control cohorts of pSS patients and healthy individuals. Methods: Peripheral blood samples were obtained and permeabilized from anti-SSA+ healthy women (at-risk) (n=7, including two ongoing pregnancies with congenital heart block (CHB) and one with a prior CHB pregnancy), pSS patients (n=11) and age- (median: 35.1 years) and gender-matched healthy donors (HD) (n=21) for intracellular staining. T and B cell subsets were identified, together with an analysis of interferon (IFN) signaling pathway molecule expression, including Signal Transducers and Activators of Transcription 1 (STAT1), STAT2, pSTAT1, pSTAT2, Interferon Regulatory Factor 9 (IRF9) and IRF1 using flow cytometry. Statistical analyses were applied to examine the distribution of immune cell frequencies, their subsets and correlations among signaling molecules and clinical data. Results: The at-risk group exhibited a significantly higher IFN signature, as identified by Siglec-1 (CD169) expression on CD14+ monocytes, compared to healthy donors but similar to its expression found in pSS patients. Importantly, STAT1 expression among all B cell subsets including naïve (CD27-IgD+), pre-switched (CD27+ IgD+), switched-memory (CD27+IgD-), double negative (CD27- IgD-) B cells and in particular by plasmablasts (CD27++ CD38++) was elevated in the at-risk group compared to HD (Figure 1A). There was no difference of STAT1 expression among at-risk patients compared to patients with pSS. Furthermore, IRF9 was increased among DN B cell subsets in at-risk women. Interestingly, there was no difference for STAT2 or IRF1 expression in at-risk patients versus the other two cohorts. Similar results were found for T cell subsets. Here STAT1 and IRF9 expression were elevated in CD4+ and CD8+ T cells in at-risk women compared to healthy controls, but similar to those found among pSS patients. Noteworthy, at-risk women presented with similar T and B cell frequencies as HD, while pSS patients exhibited an increase in naïve B cells and a diminished memory B cell frequency. Finally, there was a correlation between STAT1 and with the type I IFN regulated Siglec-1 (CD169) expression, especially in plasmablasts, in the at-risk group. Conclusion: Our data suggest increased transcriptional activity of type I IFN signaling molecules in T and B cell subsets among at-risk women and pSS patients producing anti-SSA antibodies, likely entertaining the pro-inflammatory programming. The molecular similarities between the at-risk and pSS cohorts (IFN and anti-SS-A signature) but lack of overt disease manifestations in the at-risk group, underscore the necessity for additional mechanistic studies on how increased type I IFN and B cell abnormalities culminate in clinically evident disease. REFERENCES: [1] Lisney AR, Szelinski F, Reiter K, Burmester GR, Rose T, Dörner T. High maternal expression of SIGLEC1 on monocytes as a surrogate marker of a type I interferon signature is a risk factor for the development of autoimmune congenital heart block. Ann Rheum Dis. 2017;76(8):1476-80. [2] Brito-Zerón P, Izmirly PM, Ramos-Casals M, Buyon JP, Khamashta MA. The clinical spectrum of autoimmune congenital heart block. Nat Rev Rheumatol. 2015;11(5):301-12. Acknowledgements: NIL. Disclosure of Interests: None declared.