Use of immunoblot detection of serum antibodies in the diagnosis of chronic Pseudomonas aeruginosa lung infection in cystic fibrosis

Antibodies to Pseudomonas aeruginosa were investigated in serum from cystic fibrosis (CF) patients by immunoblotting (Western blotting). The results were compared with determinations of precipitating antibodies in serum by crossed immune electrophoresis (CIE). The number of CIE precipitins is a sensitive and specific indication of infection and is used, with sputum bacteriology, to distinguish between colonisation and invasive lung infection. Immunoblotting was considerably more sensitive than CIE for detecting antibodies to P. aeruginosa. Paired serum samples from 64 CF patients, taken before a diagnosis of P. aeruginosa lung infection and immediately afterwards, showed a marked increase in the number of serum antibodies with the onset of infection. The intensity of the reaction, as shown by the density of blotted bands, was also increased. Laser scanning densitometry of immunoblots, and of photographic negatives taken from them, was used to quantify the increases. Differences in the number and intensity of blotted bands were highly significant between the two groups. The reproducibility of the method was good. An immunoblot assay may be a sensitive and useful method for routine diagnosis of early P. aeruginosa lung infection in CF.