Variations of cells populations and cytokines in bronchoalveolar lavage (BAL) from calves challenged with BRSV-Snk. Experimental challenge by inhalation of aerosolized BRSV passaged in gnotobiotic calves (BRSV-Snk) was performed in five calves with moderate levels of BRSV-specific maternal antibodies (MDA). Samples of the cells populating the lower airways were collected via BAL seven days after infection, and in addition, from three healthy uninfected calves (Control). Cells in BAL samples were analyzed by light microscopy (panel A), and expressed as group mean ×106 cells/ml. The concentrations of indicated inflammatory cytokines in BAL sample supernatants were measured using specific ELISAs, and are expressed in ng/ml: (panel B) interleukin (IL)-4; (panel C) IL-6; (panel D) IL-8; (panel E) interferon gamma (IFNγ); and (panel F) tumor necrosis factor alpha (TNFα). Individual data are indicated by rings and group means by horizontal lines. Probability (p) of statistically significant differences between groups is given in each panel, where p ≤ 0.05 was considered statistically significant.