C5AR1 and asthma: In addition, we found that RSV infection apparently enhanced the frequencies of Th1, Th2, and Th17 cells but decreased the Treg cells frequencies by stimulating C5a and C5aR1 production, and the above changes were alleviated by a C5aR antagonist (C5aRA) in an asthma mouse model (Hu et al., 2017).