Avidity of anti-P aeruginosa antibodies during chronic infection in patients with cystic fibrosis

Background-In order to study the impact on the lung function of patients wi th cystic fibrosis of the avidity of antipseudomonal antibodies, the avidit y of antibodies against the chromosomal beta-lactamase of Pseudomonas aerug inosa (a beta ab) and against the 60-65 kDa heat shock protein of P aerugin osa (anti-GroEL) were measured in serum samples collected longitudinally du ring chronic infection with P aeruginosa from a group of patients with poor and good lung function. Methods-The thiocyanate elution method in which the molarity of potassium t hiocyanate required to elute 50% bound antibody under conditions of antigen excess in ELISA was used to measure the relative avidity. Results-All patients developed increasing levels of a beta ab and anti-GroE L antibodies during the follow up period but no maturation of the avidity o f these antibodies was observed. In patients with good lung function the av idity of a beta ab was higher than in patients with poor lung function (p = 0.018). No significant difference in the acidity of the anti-GroEL antibod ies was observed between the two groups of patients. Conclusion-In patients with cystic fibrosis a high avidity of a beta ab cou ld contribute to a more efficient inhibition of the beta-lactamase by these antibodies, resulting in the better lung function seen in this group. The immunopathological implication of the failure in avidity maturation of anti bodies in chronic infection is discussed.