DETECTION OF DONOR-DERIVED LANGERHANS CELLS IN MHC CLASS-II IMMUNODEFICIENT PATIENTS AFTER ALLOGENEIC BONE-MARROW TRANSPLANTATION

T-cell dependent immune response is initiated by dendritic cells, whic h are the only leucocytes able to prime naive CD4-positive T cells, La ngerhans cells (LC) are dendritic cells characterized by their localiz ation within the epidermis, their dendritic shape, and their expressio n of specific markers such as major histocompatibility complex (MHC) c lass II molecules, CD1a and S100 protein. We retrospectively studied t he phenotype of LC in the skin of eight children with MHC class II def iciency (bare lymphocyte syndrome) after allogeneic bone marrow transp lantation (BMT). The presence of donor-derived MHC class II positive L C within the epidermis was studied by immunohistochemistry on skin bio psies performed for the determination of graft-versus-host disease, MH C class II positive LC were undetectable in the epidermis of a child w ho did not engraft and of three children 13-18 d after HLA-mismatched BMT. despite engraftment. However, donor-derived MHC class LT positive LC were detected in four children 9-43 d after HLA-identical BMT. Our results demonstrate that LC can differentiate or expand very quickly, as early as within 9 d after BMT.