
<ArticleTitle>Presence of <prot>HLA-DR</prot> immunopositive cells in human fetal thymus.</ArticleTitle>
<AbstractText>Several kinds of thymic cells express MHC class II antigens, including <prot>human-leukocyte-associated antigen-DR</prot> (<prot>HLA-DR</prot>) during postnatal development. The present study was focused on the detection and analysis of <prot>HLA-DR</prot> immunoreactivity in human fetal thymuses (6-7th month of gestation). Using monoclonal antibodies, indirect immunoperoxidase staining (IIP), immunogold electron microscopy (IGEM), enzyme-linked immunosorbent assay (ELISA) and flow cytometry, <prot>HLA-DR</prot> immunopositive (IP) thymic cells were found in samples studied. IIP and IGEM demonstrated the presence of <prot>HLA-DR</prot> IP stromal cells (SCs): epithelial cells (ECs), dendritic-like cells (DCs) and macrophages (MCs) as well as <prot>HLA-DR</prot> IP lymphocytes (Lys) in all thymic regions. <prot>HLA-DR</prot> immunoreactivity was more prominent in the medullary ECs (mECs) than in the cortical ECs (cECs). Strong staining of Hassall's corpuscles and the adjacent mECs was seen. The differences in the intracellular distribution of <prot>HLA-DR</prot> molecules were detailed by IGEM as a first attempt to analyse <prot>HLA-DR</prot> IP cells at ultrastructural level. ELISA data and two-colour flow cytometric analysis revealed the presence of <prot>HLA-DR</prot> IP and <prot>HLA-DR</prot>/<prot>CD3</prot> double IP Lys in accordance with the immunocytochemical assays. The results presented enrich the information about <prot>HLA-DR</prot> IP components of the thymic microenvironment in developing human thymus and raise the question of their role during prenatal T cell differentiation and selection processes.</AbstractText>
