Expression of Gr-1 on lymphocytes recovered from the lungs of influenza virus-infected mice. (A) Binding of fluorescent-labelled RB6-8C5 to NK1.1+ lymphocytes, CD4+ or CD8+ T lymphocytes and B cells (B220+ lymphocytes) from lungs of uninfected mice (white histograms) or mice 3 days after infection with 105 PFU of HKx31 (grey histograms). Samples represent pooled lung cell suspensions from groups of 3–5 uninfected or virus-infected mice. (B) Cellularity of lung cell suspensions from IgG-treated and RB6-8C5-treated mice 5 days after infection with 105 PFU of HKx31. Mice treated with either IgG or RB6-8C5 (at days -1, +1 and +3, as described in Materials and Methods) were infected at day 0 with 105 PFU of HKx31 and lung cell suspensions were prepared from lung tissue at day 5 post-infection. Shown are the mean numbers (± SD) of total leukocytes (CD45+), NK cells (NK1.1+ lymphocytes), B cells (B220+ lymphocytes), CD4+ T cells and CD8+ T cells recovered from the lungs of IgG-treated or RB6-8C5-treated mice (n = 5 mice/group). Data are representative of at least 2 independent experiments. ** p = 0.015 for NK cells, p = 0.017 for CD8+ T cells.