A human lymphocyte (pink pseudo-color) scans the surface of a dendritic cell (blue pseudo-color). The image was obtained using a field emission scanning electron microscope. Scale bar = 1µm.
Dendritic cells trigger an adaptive immune response by activating two major classes of T lymphocytes—cytotoxic T cells that can kill infected host cells, and helper T cells that direct the activities of other immune cells. Cytotoxic T cells recognize class I MHC receptors loaded with antigen, whereas helper T cells recognize class II MHC-peptide. Dendritic cells constitutively express high levels of both class I and class II MCH molecules, making them the most potent activators of T cells, capable of stimulating even ‘naive’ T cells that have never encountered antigen.
By Olivier Schwartz and the Electron Microscopy Core Facility, Institut Pasteur