Immunologic Aspects of Organ Transplantation

Susan Smith MN, PhD


June 17, 2002

Other Mediators of Innate Immunity

Other mediators of innate immunity include null cells, natural killer (NK) cells, the IFNs, and acute phase proteins.[4,5] Null cells are also referred to as third population cells because, although they are thought to be lymphoid cells, their exact lineage is unknown. They are neither T cells, B cells, nor macrophages. Null cells kill antibody-coated target cells. NK cells are large (usually granular) non-B, non-T lymphocytes that do not have T-cell receptors (TcRs) or antibodies on their surfaces. NK cells account for about 3% of the differential WBC count. NK cells are activated by IFN to spontaneously kill tumor-or virus-infected cells. Prior sensitization is not necessary for activation of NK cells.[5] IFNs are a group of proteins produced by virally infected cells and lymphocytes. IFNs are produced very early in infection and induce a state of immunity in surrounding noninfected cells by interfering with viral replication. Acute phase proteins are a group of proteins that proliferate in the serum during acute infection. Acute phase proteins promote complement binding and opsonization.