Production of lung eosinophilia in the mouse model of respiratory syncytial virus (RSV). Lung eosinophilia is linked to the inability of the major surface glycoprotein G of RSV (RSV G-protein) to stimulate T-helper (Th)1, or CD8+, cells to produce IFN-γ. Once activated, Th1 cells stimulate macrophages and dendritic cells to produce IL-12. This induces natural killer (NK) cells and Th1 cells to produce IFN-γ. In the presence of IFN-γ lung eosinophilia is inhibited; in its absence the Th2 response persists. Th2 cells produce IL-4 and IL-5, which causes lung eosinophilia. Adapted with permission from Openshaw et al. . rVV, recombinant vaccinia virus.