Plasmacytoid monocytes migrate to inflamed lymph nodes and produce large amounts of type I interferon

We have identified two cell subsets in human blood based on the lack of lin eage markers (lin(-)) and the differential expression of immunoglobulin-lik e transcript receptor 1 (ILT1) and ILT3. One subset (lin(-)/ILT3(+)/ILT1(+) ) is related to myeloid dendritic cells. The other subset (lin(-)/ILi3(+)/I LT1(-)) corresponds to 'plasmacytoid monocytes'. These cells are found in i nflamed lymph nodes in and around the high endothelial venules. They expres s CD62L and CXCR3, and produce extremely large amounts of type I interferon after stimulation with influenza virus or CD40L. These results, with the d istinct cell phenotype, indicate that plasmacytoid monocytes represent a sp ecialized cell lineage that enters inflamed lymph nodes at high endothelial venules, where it produces type I interferon. Plasmacytoid monocytes may p rotect other cells from viral infections and promote survival of antigen-ac tivated T cells.