Physical interaction between Langerhans cells and T-lymphocytes during antigen presentation in vitro

Physical interaction between Langerhans cells and T cells is an essential requirement for antigen presentation. In this study we report the ultrastructural characteristics of the antigen-specific physical interactions that occur in vitro between murine Langerhans cells and T cells. Epidermal Langerhans cells enriched to 78% purity by a panning method were pulsed with 2,4-dinitrophenyl-Limulus polyphemus hemocyanin and co-incubated with syngeneic T lymphocytes primed in vivo with the same antigen. A substantial number of conjugates constituted by Langerhans cells surrounded by three or more lymphocytes were obtained after 60 min of incubation at 4 degrees C. Electron microscopy of the conjugates revealed that Langerhans cells and T lymphocytes interacted by two type of contacts. Type I was characterized by glycocalyx-glycocalyx interaction that occurred in relation to protrusions or microvilli of both cells. Type II was characterized by wide and tight areas of close apposition between Langerhans cells and T-lymphocyte plasma membranes. In these areas there were zones with intercellular bridges and small septilaminar junctions highly suggestive of gap junctions. An electron-immunogold procedure demonstrated the presence of DNP-LPH antigen on the type I contact. Our findings suggest that type I contact may represent the locus for antigen presentation whereas the type II contact may be involved in keeping adhesiveness between Langerhans cells and lymphocytes during antigen presentation.