Figure 1

VLA-4 is the primary integrin for inflammatory monocyte derived macrophages. Analysis at day 7 p.i. showed (A) CD4⁺ and CD8⁺ T cells, Ly6G⁺ neutrophils (~6%, 7% and 3%, respectively, of all infiltrating leukocytes), and large numbers of Ly6C⁺ macrophages (~50% of infiltrating leukocytes, of which >90% were Ly6C^hi) infiltrating into the brain from day 5 p.i., and (B) lymphocyte function-associated antigen (LFA)-1 and very late antigen (VLA)-4 was expressed on Ly6C^lo and Ly6C^hi blood monocytes. (C) Immunohistochemical staining for intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1 performed on day 7 p.i. on the sham-infected and WNV-infected brains of C57BL/6 mice showed significant widespread upregulation of both molecules in WNV-infected mice and co-localized with CD31. Treatment with 100 μg anti-VLA-4 antibody from day 6 p.i. onwards resulted in reduced neutrophil and T cell recruitment into day 7 p.i. WNV-infected brains. A 66% reduction was seen in the CD45⁺/CD11b⁺/Ly6G⁻/Ly6C^hi macrophage compartment. (D) By contrast, LFA-1 blockade reduced Ly6C^hi macrophage infiltration by 33%. (E) VLA-4 blockade resulted in increased survival of 10 to 60%, depending on the inoculation dose (P < 0.001), whereas (F) LFA-1 blockade did not increase survival. (G) Viral titers in the brain at day 7 p.i. were similar in all treatment groups. Data are representative of at least three independent experiments with at least four mice per group. Antibody-mediated effects on the disease course were determined on four separate occasions with at least ten mice per group. Data shown are the mean ± standard deviation. Statistical analysis was conducted using one-way ANOVA with a Tukey-Kramer post hoc test. Statistical analysis of survival was conducted using the log-rank (Mantel-Cox) test. * P < 0.05; **P < 0.001; ***P < 0.001. The inoculation dose used was 6 × 10³ plaque-forming units, unless otherwise noted.