Direct Microbicidal Activity of Cytotoxic T-Lymphocytes
Figure 1
Killing of extracellular and intracellular microbes by CTL. (A) CTL bind to an extracellular microbe (grey) via an unknown receptor (?) independently of MHC (panel A1). Binding triggers CTL to release granulysin (blue) which binds to and kills the microbe (panel A2). By contrast, CTL killing of intracellular microbes involves MHC-restricted antigen-specific recognition of infected host cells. (B) CTL-host cell interactions induce the release of perforin (green) and granulysin (panel B1). Perforin-generated pores in the host cell membrane facilitate the influx of extracellular which induces endocytosis of the membrane region damaged by perforin, along with nearby granulysin (panels B2–B4). Granulysin-containing endosomes fuse with intracellular compartments containing the microbe allowing granulysin to bind to and kill the microbe (panel B5). (C) Alternatively, CTL induce lysis of an infected host cell causing the release of intracellular microbes which are then killed by other nearby CTL (panels C1–C3).
