Plasmacytoid dendritic cells are members of the innate immune system and are particularly important in anti-viral immunity since they are the most potent producers of type I interferons. This book describes the phenotype of knockout mice for Ly49Q, a cell surface receptor expressed on pDCs. In vivo, knockout mice with PGK-Neomycin insertion control early murine cytomegalovirus infection better, but no difference could be detected in mice with recombined LoxP sites. Thus, we observed a differential immune response dependent on the gene knockout strategy. In mice with PGK-Neomycin insertion, we found enhanced hematopoiesis of some populations of the myeloid lineage and lower activation of pDCs following treatment with particular Toll-like receptor ligands, which translates into diminished T cell stimulatory capacity. This suggests a role for Ly49Q in regulating hematopoiesis and pDC activation potential.