Mouse type IIFN-producing cells are immature APCs with plasmacytoid morphology

dWe show here that mouse interferon-alpha (IFN-alpha)-producing cells (mIPC s) are a unique subset of immature antigen-presenting cells (APCs) that sec rete IFN-alpha upon stimulation with viruses.. mIPCs have a plasmacytoid mo rphology, can be stained with an antibody to Ly6G and Ly6C (anti-Ly6G/C) an d are Ly6C(+)B220(+)CDIIc(10)CD4(+); unlike other dendritic cell subsets, h owever, they do not express CD8 alpha or CDIIb. Although mIPCs undergo apop tosis in vitro, stimulation with viruses, IFN-alpha or CpG oligonucleotides enhanced their survival and T cell stimulatory activity. In vivo, mIPCs we re the main producers of IFN-alpha in cytomegalovirus-infected mice, as dep letion of Ly6G(+)/C+ cells abrogated IFN-alpha production. mIPCs produced i nterleukin 12 (IL-12) in response to viruses and CpG oligodeoxynucleotides, but not bacterial products. Although different pathogens can selectively e ngage various APC subsets for IL-12 production, IFN-alpha production is res tricted to mIPCs' response to viral infection.