PRIMARY SENSITIZATION OF HUMAN T-LYMPHOCYTES BY CYTOKINE-CULTURED, PERIPHERAL-BLOOD MONOCYTES

Langerhans cells are bone marrow-derived, antigen-presenting cells cha racterized by expression of amongst others, CD1a and HLA-DR. Recently, interest has focused on Langerhans precursor cells circulating in the peripheral blood. We have isolated monocytes from human, peripheral b lood mononuclear cells by removal of CD3(+), CD19(+) and CD56(+) cells using immunomagnetic beads. After culture of the monocytes for 3 and 5 days with either 10 to 200 ng/ml granulocyte-macrophage colony-stimu lating factor (GM-CSF) or 100 ng/ml GM-CSF and 100 U/ml interleukin-4 (IL-4), respectively, a varying fraction of the cells developed a dend ritic morphology and there was a distinct formation of clusters. CD1a as well as HLA-DR were upregulated. Functionally, the alloactivating a nd antigen-presenting capacity of the cytokine-cultured cells, as asse ssed in 7-day-cultures with either allogeneic T lymphocytes or autolog ous T lymphocytes and tetanus toroid, reproducibly and substantially e xceeded that of control monocytes from the same donor cultured for 3 o r 5 days without exogenous cytokines, while there was no difference be tween the two types of cytokine culture. Attempts at demonstrating pri mary sensitization in vitro were conducted by repeated addition of tri nitrophenyl-haptenized, either cytokine-cultured or freshly isolated m onocytes to autologous T lymphocytes. The GM-CSF cultured cells induce d a significant T lymphocyte proliferation exceeding that seen in cell s cultured with GM-CSF and IL-4, whereas there was a weak response wit h only some of the freshly isolated monocytes. These results lend supp ort to the hypothesis that the culture of human, peripheral blood mono cytes with the cytokines GM-CSF and IL-4 might induce the maturation o f Langerhans precursor cells, resulting in enhanced antigen-presenting capacity.