Control of the differentiation state and function of human epidermal Langerhans cells by cytokines in vitro

Langerhans cells can originate in vitro from immature precursors stimulated with granulocyte macrophage-colony-stimulating factor (GM-CSF), tumour nec rosis factor (TNF)-alpha and stem cell factor (SCF). We asked whether these cytokines also control the differentiation state of Langerhans cells withi n the epidermis and upon leaving this tissue. We harvested sheets of human epidermis by controlled dispase hydrolysis of keratomes, cultured them in R PMI and 10% fetal calf serum for 48 h and analysed the sheets and the cells migrated spontaneously into the medium, most of which were Langerhans cell s containing Birbeck granules.' By flow cytometry, the intensity of CD1a ex pression was reduced quite evenly among Langerhans cells migrated from shee ts within 48 h. The cells in the sheets underwent loss of dendrites, with a significant reduction in the cell perimeter that was prevented by GM-CSF a nd TNF-alpha together. Either of these cytokines induced expression of CD18 by cells in the sheets and those in the medium. Moreover, TNF-alpha induce d expression of CD54 by cells in the medium, but not by those retained in t he sheets, whereas human SCF induced, dose dependently, expression of CD54 by cells in the sheets, but not from those in the medium.(2) The proliferat ion of allogeneic lymphocytes was much higher when stimulating Langerhans c ells were harvested from cultures with any cytokine, rather than from cultu res without cytokines. We conclude the following: (i) GM-CSF and TNF-alpha help to maintain full differentiation of Langerhans cells within the epider mis; (ii) cytokine influence on Langerhans cells adhesiveness is in part co ntext dependent; and (iii) pretreatment with cytokines influences positivel y the number or accessory activity of Langerhans cells on lymphocytes durin g subsequent mixed leucocyte reaction.