Fig. 2.

Bystander killing: virus-specific CD8⁺ T cells migrating to the infected target tissues and exerting perforin and granzyme-mediated cytotoxicity. The CD4⁺ T cells contribute to this bystander killing by the release of proinflammatory cytokines and enhancing phagocytic activities of the macrophages. The free oxygen radicals and cytokines secreted from the activated macrophages result in bystander killing off the surrounding non-infected cells. Ineffective clearance of these killed cells exposes autoantigen to the antigen-presenting cells, resulting in the generation of autoreactive cells in the presence of the costimulatory molecules