Imaging using two-photon microscopy of encephalitogenic MOG35-55 specific T lymphocytes (blue, due to expression of cyanin fluorescent protein) in the spinal cord during experimental autoimmune encephalomyelitis, a model for multiple sclerosis. MOG specific T lymphocytes move rapidly within the CNS parenchyma searching for their target antigen. Some activated T cells create brief contacts with microglial cells (green, due to green fluorescent protein expression), while others establish more stable interactions with microglia. Because microglia function as antigen presenting cells in the central nervous system, these more stable interactions between T lymphocytes and microglia are considered to represent antigen recognition events. A rhodamine dextran labeled blood vessel appears red.