Human leucocyte antigen (HLA) expression of primary trophoblast cells and placental cell lines, determined using single antigen beads to characterize allotype specificities of anti‐HLA antibodies

TLDR

Human trophoblast cells display a unique HLA repertoire that is difficult to define because classical HLA‑I loci are highly homologous and polymorphic, making antibody reactivity against the thousands of allotypes hard to determine. Using commercially available single‑antigen beads coated with individual HLA‑I molecules, the authors tested nine monoclonal antibodies against 96 common allotypes, combined with donor genotyping, to map antibody binding and analyze HLA expression in primary trophoblasts, choriocarcinoma cells, and placental cell lines. The study shows that primary villous trophoblasts are HLA‑null, extravillous trophoblasts express HLA‑C, ‑G, and ‑E but not ‑A, ‑B or ‑DR, tumor‑derived JEG‑3 and JAR cells mimic extravillous and villous phenotypes respectively, yet placental cell lines do not recapitulate either phenotype, questioning their validity as immunological models.

Abstract

Human trophoblast cells express an unusual repertoire of human leucocyte antigen (HLA) molecules which has been difficult to define. Close homology between and extreme polymorphism at the classical HLA class-I (HLA-I) loci has made it difficult to generate locus-specific monoclonal antibodies (mAbs). The problem of defining an antibody's reactivity against the thousands of existing HLA-I allotypes has often made it impossible to determine the HLA bound by a mAb in biological samples from a normal outbred population. Here we have used commercially available beads coated with individual HLA-I to characterize experimentally the reactivity of nine mAb against 96 common HLA-I allotypes. In conjunction with donor HLA-I genotyping, we could then define the specific HLA molecules bound by these antibodies in normal individuals. We used this approach to analyse the HLA expression of primary trophoblast cells from normal pregnancies; the choriocarcinoma cells JEG-3 and JAR; and the placental cell lines HTR-8/SVneo, Swan-71 and TEV-1. We confirm that primary villous trophoblast cells are HLA null whereas extravillous trophoblast cells express HLA-C, HLA-G and HLA-E, but not HLA-A, HLA-B or HLA-DR molecules in normal pregnancy. Tumour-derived JEG-3 and JAR cells reflect extravillous and villous trophoblast HLA phenotypes, respectively, but the HLA repertoire of the in vitro derived placental cell lines is not representative of either in vivo trophoblast phenotype. This study raises questions regarding the validity of using the placental cell lines that are currently available as model systems for immunological interactions between fetal trophoblast and maternal leucocytes bearing receptors for HLA molecules.