FIGURE 1.

SP-A-modulated cell surface expression of complement receptors on alveolar macrophages. Alveolar macrophages were recovered by bronchoalveolar lavage, incubated with the indicated fluorescently labeled anti-complement receptor antibody, and analyzed by flow cytometry. Decreased surface expression of CR3 (panel A) and CR4 (panel B) was observed on alveolar macrophages from Sp-a^–/– (solid bar) compared with Sp-a^+/+ (hatched bar) mice in uninfected, GBS-infected, and H. influenzae (H FLU)-infected mice. CR3 expression on alveolar macrophages was assessed at intervals for 24 h following H. influenzae infection (10⁴ cfu). CR3 expression on alveolar macrophages fell slightly over the first 2 h post-infection and then increased through 6 h. CR3 expression on AM from Sp-a^–/– mice (circle) reached a plateau at 6–24 h, but was significantly less at every time point following H. influenzae infection compared with Sp-a^+/+ (triangle) mice (panel C). Total CR3 was similar for Sp-a^–/– (solid bar) and Sp-a^+/+ (hatched bar) alveolar macrophages and the internal pools of CR3 were increased in alveolar macrophages from Sp-a^–/– mice (panel D). Data are mean ± S.E. with n = 8 mice per group, *, p < 0.05 compared with Sp-a^+/+ mice for all panels.