Sustained TLR7 stimulation induces lymphopenia and increased neutrophil and monocyte numbers. (A-D) Mice were treated with the TLR7 ligand R848 in a daily fashion. After 7 days of treatment, blood was analyzed for the presence of leukocytes, lymphocytes, monocytes, neutrophils, and thrombocytes 1 hour after the last injection. (A) R848 treatment did not affect absolute numbers of circulating leukocytes. Left: 1 mg R848/kg per day; analysis by flow cytometry before and after treatment. Numbers signify percentage of viable leukocytes as determined by FSC/SSC characteristics. Arrowhead indicates monocytes and neutrophils (ie, large granular cells with high FSC/SSC properties). Right: analysis by hemocounter. (B) Total lymphocytes and all major lymphocytic cellular subsets (ie, B220⁺ B cells, CD4⁺, and CD8⁺ T cells) were massively decreased, whereas (C) monocyte and neutrophil numbers increased. Effects are dose and TLR7 dependent. Lymphocyte, monocytes, and neutrophils numbers were determined mechanically; absolute numbers of lymphocyte subpopulations were determined using BD truCOUNT technology. (D) Thrombocyte numbers were determined with hemocounter. (E) Similar analysis after 21 days of TLR7 stimulation. Error bars indicate standard error. Data of at least 3 individually measured animals are shown. pIC indicates polyI:C.