S100A9 and cystic fibrosis: Second, since S100A8 and S100A9 act as potent leukocyte chemokines and their elevation at 20-days of age are the earliest reported signs of a lung inflammatory phenotype in CF mice, this elevation may be directly responsible for eliciting the massive neutrophil influx observed in 4–5 week old B6-CF lungs [26,27,42].