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

Abstract

Summary 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.

Toll-like receptor profiling of seven trophoblast cell lines warrants caution for translation to primary trophoblasts

“…The placenta contains different trophoblast types with specialized functions [3], and trophoblast cell lines can only partly reflect this complexity. Functional and phenotypic differences between trophoblast cell lines and primary trophoblasts have been extensively studied [38][39][40][41][42][43].…”

The role of the maternal immune system in the regulation of human birthweight

“…EVT in the decidua also express an unusual MHC profile: they lack class II expression and do not express the human leukocyte antigen-A (HLA-A) or -B molecules normally found on all somatic cells [25]. Instead EVT express classical HLA-C as well as non-classical molecules, HLA-E and -G. The latter two are essentially monomorphic in human populations so will not vary from pregnancy to pregnancy [25].…”

“…Instead EVT express classical HLA-C as well as non-classical molecules, HLA-E and -G. The latter two are essentially monomorphic in human populations so will not vary from pregnancy to pregnancy [25]. Since most T cells are restricted to recognize self-HLA-A or -B molecules in association with a non-self-peptide, the unusual MHC profile of EVT means that only HLA-C-restricted T cells are capable of directly recognizing EVT in the decidua.…”

“…Of these, our focus has been on those receptors that could be involved in specific recognition of paternal difference [5,16]. We have therefore studied NK receptors that can bind the MHC molecules expressed by EVT: HLA-C, -E and -G. The latter two are essentially monomorphic in human populations so will not vary from pregnancy to pregnancy [25]. Uterine NK cells express killer-cell immunoglobulin-like receptors (KIRs) that can recognize HLA-C, and invading trophoblast cells abundantly express both maternal and paternal HLA-C molecules [35].…”

Paternal MHC expression on mouse trophoblast affects uterine vascularization and fetal growth

“…An important mechanism may be provided by the distinctive MHC antigen expression profile on the surface of trophoblast. In humans, invasive extravillous trophoblast cells lack the highly polymorphic classical MHC class I (HLA-A and -B) and class II antigens but instead express a unique combination of classical HLA-C and nonclassical HLA-G and HLA-E molecules (8)(9)(10). Because nonclassical MHC class I molecules are invariant and HLA-G is expressed in the thymus, these antigens do not elicit prominent maternal immune responses (11,12).…”