P146 Low CD4+ T cell count is related to specific anti-nuclear antibodies, IFNα protein positivity and disease activity in systemic lupus erythematosus pregnancy

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Objective Adverse pregnancy outcomes are more common among women with systemic lupus erythematosus (SLE) compared to healthy women, but there is limited understanding on how pregnancy affects the immune system and what specific immunopathological processes that precede these complications. Lymphopenia, autoantibodies and activation of the type I interferon (IFN) system are common features SLE. We aimed to investigate the impact of pregnancy on lymphocyte subset counts in SLE and their associations with autoantibody profiles and IFNα concentrations. Methods Repeated blood samples were collected from 80 pregnant women with SLE and 51 healthy controls (HC), with additional samples from 19 women with SLE postpartum. Flow cytometry was used to measure CD4+ and CD8+ T cells, B cells, and NK cells. Positivity for anti-nuclear antibodies (ANA) fine specificities and anti-phospholipid antibodies was assessed using multiplexed bead assay. IFNα concentration was quantified with Single molecule array (Simoa) immune assay. Clinical data were retrieved from medical records. Results Women with SLE had lower counts of all lymphocyte subsets compared to HC throughout pregnancy, but counts did not differ during pregnancy compared to postpartum. Principle component analysis revealed that low lymphocyte subset counts differentially related to autoantibody profiles, cluster one (anti-dsDNA/anti-Sm/anti-RNP/anti-Sm/RNP/anti-chormatin), cluster two (anti-SSA/anti-SSB) and cluster three (anti-CL/anti-β2GPI), IFNα protein levels and disease activity. CD4+ T cell counts were lower in women positive to all ANA fine specificities in cluster one compared to those who were negative, and B cell numbers were lower in women positive for anti-dsDNA and anti-Sm compared to negative women. Moreover, CD4+ T cell and B cell counts were lower in women with moderate/high compared to no/low disease activity, and CD4+ T cell count was lower in IFNα protein positive relative to negative women. Finally, CD4+ T cell count was unrelated to treatment. Conclusion Lymphocyte subset counts are lower in SLE compared to healthy pregnancies, which seems to be a feature of the disease per se and not affected by pregnancy. Our results also indicate that low lymphocyte subset counts relate differentially to autoantibody profiles, IFNα protein levels and disease activity, which could be due to divergent disease pathways.

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