To design effective vaccines, we need to understand immune response to virus infection. CD8 cells, Cytotoxic T Lymphocytes or CTL cells. The details of these responses will be familiar to you from elsewhere. Agammaglobulinaemic children are not especially at risk of viral infections such as measles. In contrast if they lack T cells then measles is fatal.
T cells are able to recognise virus infected cells early in the infection process.
I is present on all nucleated cells with the exception of neurons. I is present on antigen presenting cells such as macrophages T and B cells. Suggests that MHC I is more important in clearing viral infections. If the MHC I system is knocked out then animals can still clear virus infections but less quickly. They can clump viruses, coat them preventing infection, activate complement.