Altogether, the lack of C5a, ICAM-I and cytokine proteolytic activity exhibited by the lasR deficient variants might explain why the emergence of LasR deficient variants in the CF lung microbiome is associated to a poor prognostic and to the increased episodes of acute exacerbations which are typically characterized by an intense lung neutrophilia [31]. This evidence concerns the gene C5 and cystic fibrosis.