IN-VITRO PRIMARY SENSITIZATION AND RESTIMULATION OF HAPTEN-SPECIFIC T-CELLS BY FRESH AND CULTURED HUMAN EPIDERMAL LANGERHANS CELLS

We examined the capacity of human Langerhans' cells (LC) to sensitize autologous T cells to the trinitrophenyl hapten (TNP) in vitro. Two-da y cultured Langerhans' cells, but not freshly prepared Langerhans' cel ls, can induce in vitro primary proliferative reactions to the TNP hap ten. Using a CD45RA+ naive T-cell subset, similar results were found, therefore making the possibility of a previous in vivo T-cell contact with the hapten unlikely. The primary in vitro response was strongly i nhibited by monoclonal antibodies to major histocompatibility complex (MHC) class I and II, CD4 antigens and ICAM-1 and LFA-3 adhesion molec ules. Furthermore, we found that fresh LC can prime T cells to TNP, as revealed by a significant secondary T-cell proliferation after restim ulation of the recovered T lymphocytes by fresh hapten-modified autolo gous LC. Nevertheless, the ability of these fresh LC to stimulate in v itro secondary hapten-specific T-cell proliferation was very limited i n comparison with that of 2-day incubated Langerhans' cells. After sec ondary stimulation with TNP-cultured LC, sensitized T cells could be n on-specifically expanded without losing hapten specificity. The TNP-sp ecific T-cell lines were mostly of the CD4+ phenotype. The present fin dings extend previous studies in the mouse, showing that cultured LC a re potent antigen-presenting cells (APC) in primary hapten-dependent p roliferation assays. Furthermore, this in vitro priming assay, using c ultured human Langerhans' cells as APC, might be useful to analyse the early steps of T-cell sensitization and subsequently to develop in vi tro predictive tests allowing detection of sensitizing compounds.