Cells belonging to the innate immune system such as epithelial cells, NK, NKT cells and macrophages express the functional heterodimer IL-21R and respond to IL-21 [14], [18]–[20], [22], thus they are potential targets for IL-21 in the innate stages of a viral infection (day 1-3 p.i.). The gene discussed is IL21; the disease is viral infectious disease.