Figure 8. Immune activation in the presence of virus-specific antibodies is Usp18 dependent.

Lymphocytic choriomeningitis virus (LCMV)-specific antibodies were injected into Usp18^−/− mice and littermate control mice. Non-specific antibodies were injected into littermate control mice to form a control group. Mice were challenged with LCMV-Docile. (A) Immunohistochemical analysis of spleen showing LCMV nucleoprotein (red), marginal zone macrophages (CD169, green), and follicular B cells (B220, blue) after 1 day of infection with 2 × 10⁶ plaque-forming units (PFU) of LCMV-Docile (n = 3). Scale bar, 200 μm. (B–E) Mice were infected with 2 × 10⁴ PFU of LCMV-Docile and were evaluated for various parameters after 10 days of infection. (B) Total number of LCMV-specific T cells in the spleen that were positive for the MHC class I tetramer of the glycoprotein of LCMV (Tet-GP33⁺) and for CD8 (CD8⁺) (n = 5–8). (C) Total number of interferon (IFN)-γ⁺ CD8⁺ T cells in the spleen was determined after in vitro stimulation with or without LCMV GP33 peptide for 5 hours (n = 5–8). (D) Total number of IFN-γ producing CD4⁺ T cells after in vitro stimulation with or without LCMV GP64 peptide for 5 hours in spleen (n = 5–8). (E) Viral titers from spleen, inguinal lymph nodes (LN), liver, kidneys, and lungs (n = 7–8). Data are shown as mean ± SEM and are pooled from 2 or 3 independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001 (Student’s t-test).