Components of innate immunity that are active against viral cells includes:

Properties of natural killer cells  Large granular lymphocytes. Lack T-cell receptor, CD3 proteins, and surface IgM and IgD. Prior exposure does not increase the activity. Thymus is not required for development. Number remains normal in severe combined immunodeficiency disease.  Functions of natural killer cells  Kill virus-infected cells and tumor cells. Nonspecific killing of virus-infected cells and tumor cells. Killing is independent of antigen presentation by MHC proteins. Mechanism of killing is by perforins and granzymes, which cause apoptosis of target cell. Killing is activated by failure of a cell to present antigen with class I MHC or by reduction of class I MHC proteins on the cell surface. Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page:131