Soon after the identification of CD4+Lin–CD11c–BDCA2/4+CD123+ plasmacytoid dendritic cells as the major IFNα-producing cell type in humans upon virus infection [15], [50], several groups reported the gradual decline of pDC in peripheral blood of HIV-1 patients [16], [18], [19]. The gene discussed is IFNA2; the disease is viral infectious disease.