Immune Response to Virus-Infected Cells

The immune response to virus infection protects the host against the pathogenic effects of the virus, limits dissemination of infection, and clears the infecting agent. Virus infection results in the expression of a number of different antigens, both structural (virion) and non-structural, which vary during different stages of the replicative cycle. Antibody responses are predominantly directed against structural antigens but some of these are also expressed on infected cells, which may then be lysed by complement or ADCC. Virus-specific T cells are probably the most important response against virus-infected cells. They recognize viral antigens in conjunction with MHC determinants, although the precise nature of this association is unknown. Cytotoxic T cells and T cells mediating delayed-type hypersensitivity have been shown to be directly protective but these require T helper and other cells for their generation. Lymphokines, such as interferon, released by antigen-specific T cells, may also be directly protective or act by enhancing the activity of non-specific effector cells such as macrophages and NK cells. However, antibody- and cell-mediated responses can be suppressed by viruses which directly infect immunocompetent cells and, in addition to its protective effects, the immune response can prove more damaging to the host than the infecting virus. Therefore, a detailed understanding of the many facets of the immune response to virus infection is required for the future development of effective preventative and therapeutic measures.