IFN-α/β plays a critical role in the induction of lymphopenia. (Ai) BL/6 and IFNAR–/– mice were intravenously infected with 2 × 106 PFU VSV. Blood samples were taken at the indicated time points and stained for CD3ϵ and B220. For FACS analysis, data equivalent to approximately 5 μL blood were acquired. Representative results of 1 of 2 similar experiments are shown. (Aii) Twenty-four hours after VSV inoculation, blood samples were stained for CD69 and B220 and subjected to FACS analysis. Representative data of 1 of 4 animals tested are depicted. (Aiii) Serum samples of mice infected with 2 × 106 PFU VSV were taken at the indicated time points and analyzed for IFN-α by ELISA. Results are expressed as mean ± SD (n = 2). (B) Poly(I:C)– and R-848–induced lymphopenia are dependent on IFNAR signaling. BL/6 and IFNAR–/– mice were intraperitoneally treated with poly(I:C), R-848, or PBS, and blood lymphocyte counts were determined. Representative data from 1 of 2 similar experiments are shown. (C) Poly(I:C) induces IFNAR-dependent up-regulation of CD69 in spleen. Splenocytes of PBS or poly(I:C)–treated mice were stained for CD69 and B220 and subjected to FACS analysis. Representative data of 3 similar experiments are depicted. (Di) IFN-α treatment induces lymphopenia. BL/6 mice were treated subcutaneously with 2 × 105 IU IFN-α or PBS, and blood lymphocyte counts were determined. Results are expressed as mean ± SD for 4 mice per group. (Dii) CD69 expression on B and T cells in splenocyte cultures stimulated with graded concentrations of IFN-β was determined by FACS analysis. (E) Poly(I:C)–induced lymphopenia is reversible. Syngeneic CFSE-labeled splenocytes were adoptively transferred to WT recipients. Mice were given injections of poly(I:C) or PBS, and labeled cells in blood were counted. Results are expressed as mean ± SD (n = 3) and are representative of 2 similar experiments.
