Background-In order to study the impact on the lung function of patients with cystic fibrosis of the avidity of antipseudomonal antibodies, the avidity of antibodies against the chromosomal -lactamase of Pseudomonas aeruginosa (a ab) and against the 60-65 kDa heat shock protein of P aeruginosa (antiGroEL) were measured in serum samples collected longitudinally during chronic infection with P aeruginosa from a group of patients with poor and good lung function. Methods-Thethiocyanate elution method in which the molarity of potassium thiocyanate 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 ab and anti-GroEL antibodies during the follow up period but no maturation of the avidity of these antibodies was observed. In patients with good lung function the avidity of a ab was higher than in patients with poor lung function (p = 0.018). No significant diVerence in the avidity of the anti-GroEL antibodies was observed between the two groups of patients. Conclusion-In patients with cystic fibrosis a high avidity of a ab could contribute to a more eYcient inhibition of the -lactamase by these antibodies, resulting in the better lung function seen in this group. The immunopathological implication of the failure in avidity maturation of antibodies in chronic infection is discussed.

Background -Antibodies against chromo-

M., Hanson, L. 8. & Heriby, N. The clonal antibody response to Pseudomonas aeruginosa heat shock protein is highly diverse in cystic fibrosis patients. APMIS 105: 449456, 1997.The GroEL protein of Pseudoomonas aeruginosa belongs to the bacterial 60-65 kDa heat shock protein family. A strong antibody response to GroEL has been found in cystic fibrosis (CF) patients with chronic pulmonary infection caused by P. aeruginosu. Clonotypes of IgGl and IgG2 antibodies against GroEL were studied in 60 consecutive sera from 18 C F patients with chronic P. aeruginosa infection using isoelectric focusing in combination with affinity immunoblotting. The persistent antigenic stimulation in CF patients with chronic P. aeruginosa infection induced numerous IgGl and particularly IgG2 antibody clones against GroEL. The appearance of new clones with time reflected the long duration of the chronic infection. A striking addition of new clonotypes during the observation period occurred when a new unrelated bacterium (Burkholderia cepacia) had become established as a cause of the pulmonary infection, or when the P. aeruginosa infection became chronic.