Nude mice were infected with RSV and 14 days later received no cells, splenocytes from RSV-primed BALB/c mice enriched for CD4+ T cells (depleted of CD8+ and MHC class II+ cells including B cells, monocytes, macrophages, and dendritic cells [‘CD4s’]), or the same splenocytes additionally depleted of CD4+ T cells (‘Depleted CD4s’). Antibody responses against RSV or a purified RSV fusion protein (F) were analyzed by ELISAs 5 weeks after RSV infections.