Antibody response of fibrocystic patients to homologous 0-typable and 0-defective isolates of Pseudomonas aeruginosa.

Antibody titres to Pseudomonas aeruginosa of sera from 60 adult fibrocystic patients were determined in an enzyme linked immunosorbent assay (ELISA) with whole cells of homologous isolates which had been classified according to 0-antigen state by their reactivity with 0-typing antisera. Patients who were continuously colonised with Ps aeruginosa gave the highest titres: range 1500-64000 (mean 11000) and 500-48000 (mean 9000) with homologous 0-typable and 0-defective isolates, respectively. Lower titres to both varieties of isolates were obtained with recently colonised patients, and non-colonised patients gave titres with reference laboratory strains marginally above those of healthy controls. Serum titres of patients with sequential isolates were strain dependent and did not correlate with the 0-antigen state of the strain. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot analysis of these sera and strains showed antibody binding primarily to high molecular weight 0-repeating units of lipopolysaccharide. It is concluded that the 0-antigen of the strain of Ps aeruginosa used in the ELISA test does not influence the titre obtained with fibrocystic sera, and it is recommended that serum titres should be assessed with a panel of homologous isolates from patients.