Maternal–Foetal HLA-DQB1 Incompatibility Is Associated With Pregnancy-Induced Hypertensive Disorders in a Genetically Isolated Population

In pregnancy, semi-allogenic foetal trophoblasts express a specific HLA profile mediating maternal leukocyte contact, crucial for placentation. Paradoxically, maternal immunomodulation requires foetal antigen recognition, especially involving certain HLA molecules. Pre-eclampsia, a severe hypertensive complication, has been linked to antigenic similarity. Previously, we showed no selection for HLA (in)compatibility in uncomplicated naturally conceived pregnancies. However, pre-eclamptic pregnancies were associated with increased total maternal–foetal HLA and HLA-C matching. These associations suggest a role for HLA mismatches in immune regulation leading to an uncomplicated pregnancy. To better understand HLA homozygosity in human reproduction, we aimed to determine if there is a preferential selection for HLA compatibility in a genetically isolated population, and its relation to hypertensive complications. A nested case-control study, comprising 125 uncomplicated pregnancies and 50 with hypertensive complications (29 with pregnancy-induced hypertension, 21 with pre-eclampsia) was conducted in a genetically isolated Dutch population (F_ROH 1.3–3.1). Maternal and foetal HLA-A, -B, -C, -DRB1, -DQA1, -DQB1 and maternal killer-cell immunoglobulin-like receptor (KIR) genotyping were performed. Maternal–foetal HLA (mis)match counts were compared to expected values from randomisation of paternal HLA haplotypes over maternal haplotypes of the foetuses. Mismatched CD4⁺ T cell epitopes presented by maternal HLA class II were predicted using the PIRCHE-II algorithm. In uncomplicated pregnancies, no difference was found between observed and expected maternal–foetal HLA (mis)matches. However, pregnancies with hypertensive complications showed significantly higher observed HLA-DQB1 mismatches, reflected in PIRCHE-II scores. No significant differences were found in KIR/HLA-C frequencies. Interpretation is limited by the small sample size and the grouping of distinct hypertensive disorders. Nonetheless, maternal–foetal HLA-DQB1 mismatch seems to play a role in the aetiology of hypertensive complications during pregnancy in this population.