rhC5a modulates FcγR expression on AMs in vivo. (a) BAL-AM cells were isolated from C57BL/6 WT and C5aR–/– mice 4 hours after intratracheal application of 200 ng of rhC5a in 40 μl of PBS (black bars, +rhC5a) or PBS alone (white bars, –rhC5a). TaqMan RT-PCR analysis reveals significantly increased FcγRIII and reduced FcγRII mRNA levels in BAL-AMs from WT mice but not C5aR–/– mice on rhC5a treatment. Data are represented as means ± SEM (n = 6 mice for each group, *P < 0.05). (b) BAL-AM cells (2 × 104) of the indicated mice were stained with PE anti-FcγRII/III 2.4G2 mAb and analyzed on a FACScan (representative results from individual mice are shown). Different FcγRII/III staining patterns are specifically observed in FcγRII–/– and FcγRIII–/– mice after intratracheal injection of rhC5a (solid line, +rhC5a) as compared with PBS (dashed line, –rhC5a), demonstrating inverse regulation of AM surface expression of inhibitory FcγRII (reduced) and activating FcγRIII (increased) by rhC5a.