Preface: 13th International Workshop Reunion Island Reproductive Immunology, immunological tolerance and immunology of preeclampsia; 9-12 December 2024.

The preface to the 13th International Workshop on Reproductive Immunology, Immunological Tolerance, and Immunology of Preeclampsia (Reunion Island, 9-12 December 2024) pays tribute to the late Professor Chris Redman, a foundational figure in recognising preeclampsia as a heterogeneous syndrome, and reflects on the ongoing influence of his two-stage model. Presentations emphasised phenotypic distinctions and immunological mechanisms. Pierre-Yves Robillard, using a comprehensive Reunion Island perinatal database, delineated three subtypes of small-for-gestational-age infants, revealing that 77 % are constitutional while most pathological fetal growth restriction (with Doppler anomalies) occurs in normotensive mothers. His analyses further established primipaternity as a major risk factor in multiparous women, comparable to primigravidity and chronic hypertension, contrasting with the modest effects of birth interval. Gustaaf Dekker clarified that immune maladaptation primarily underlies early-onset preeclampsia, not the more common late-onset form driven by placental senescence. Gabor Than positioned early-onset preeclampsia within the great obstetrical syndromes linked to impaired deep placentation, advocating first-trimester screening and prevention strategies applicable across related disorders. Contributions from Oslo (Anne Cathrine Staff, Daniel Pitz Jacobsen) linked fetal microchimerism to placental dysfunction and maternal vascular features. Adelaide researchers (Sarah Robertson, Alison Care) highlighted regulatory T-cell deficits in spiral artery remodelling and pregnancy tolerance. Other talks explored immune intolerance in oocyte donation pregnancies (Michael Eikmans), personalised uterine immune profiling for IVF success (Nathalie Ledee), lymphocyte-driven autoantibodies and complement activation exacerbated by prior COVID-19 (Babette La Marca), endothelial glycocalyx disruption (Marco Scioscia), and ferroptosis inhibition as a novel therapeutic target via drug repurposing (Ofer Beharier). The workshop reinforced the necessity for precise clinical phenotyping-incorporating uterine artery Doppler, angiogenic biomarkers, fetal sex, birthweight centiles, and placental histology-alongside advanced immunological and genetic studies to advance understanding and management of this complex syndrome.