C5 and cystic fibrosis: To investigate whether the incapacity to cleave C5a exhibited by the isolates from chronic respiratory infections was associated to a low expression of aprA and lasB, the C5a-cleaving activity and the expression of aprA and lasB of a collection of 10 pairs of isolates, including the earliest (early) and the latest (late) isolate recovered from 10 chronically infected CF patients (see Table S1 in the supplementary material), was determined.