Comparison of BAFF and type I IFN activity in blood and placenta in SLE and healthy pregnancies

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OBJECTIVE: To examine B cell-activating factor (BAFF) and type I interferon (IFN) activity at the transcriptional and protein levels in blood and placental tissue in SLE compared with healthy pregnancies to assess their relationship and to determine whether BAFF levels are associated with pregnancy outcomes in SLE. METHODS: In the SLE-Placenta study, we followed women with SLE (n=83) and healthy controls (n=67) throughout pregnancy. Blood samples were collected in all trimesters and at delivery from peripheral blood, placental intervillous blood and cord blood. Postpartum blood samples were obtained from a subset of women with SLE. Bulk messenger RNA (mRNA) sequencing was performed on peripheral blood mononuclear cells (PBMCs) and placental tissue from a subgroup of women with SLE and healthy controls. BAFF concentrations were measured by ELISA and IFNα protein levels by single-molecule array (Simoa). RESULTS: ) and IFN-stimulated gene expression in PBMCs and placenta compared with controls. BAFF blood levels were consistently and significantly higher in SLE throughout pregnancy and inversely correlated with circulating B cell numbers. SLE pregnancies with IF-ANA or anti-dsDNA positivity displayed higher BAFF levels than antibody-negative pregnancies but BAFF showed no association with disease activity. Both BAFF and IFNα concentrations were higher in placental than peripheral blood in SLE, whereas only BAFF showed additional accumulation in cord blood. Finally, elevated BAFF levels were associated with shorter pregnancy duration in SLE but not in healthy pregnancy. CONCLUSIONS: Pregnant women with SLE exhibited persistently elevated BAFF levels, which were associated with lower B cell numbers, SLE-related autoantibody positivity and shorter pregnancy duration. Together with a disease-specific placental enrichment of IFNα, these findings support the presence of an inflammatory and potentially pathogenic IFN-BAFF signature in SLE pregnancy. Further studies are needed to determine the functional consequences of these immunological alterations on maternal-fetal health in SLE.

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