Pseudomonas aeruginosa infection in cystic fibrosis. Relationship between mucoid strains of Pseudomonas aeruginosa and the humoral immune response.

The occurrence of Pseudomonas aeruginosa in the respiratory tract of 70 cystic fibrosis patients and the occurrence of precipitins against Ps. aeruginosa in sera from the same patients have been investigated during one year by means of monthly bacteriological examinations of tracheal secretions and by means of crossed Immunoelectrophoresis of a polyvalent Ps. aeruginosa antigen against sera from the patients. The one-year period prevalence rate of patients harbouring Ps. aeruginosa was 64 per cent. In newly colonized patients and in intermittently colonized patients non-mucoid strains were predominating, whereas mucoid strains were predominating in chronically colonized patients. The occurrence of mucoid strains, especially in chronically colonized patients, was associated with a significantly higher number of precipitins against Ps. aeruginosa than the occurrence of non-mucoid strains. Males chronically colonized with mucoid strains presented a significantly higher number of precipitins than females chronically colonized with mucoid strains and the number of precipitins was correlated with the duration of the chronic colonization with Ps. aeruginosa in males in contrast to females. The results are in accordance with the hypothesis that mucoid substance could be a virulence factor because it might inhibit the opsonizing effect of the precipitins on the mucoid cells and the complement dependent lysis of the cells hereby favouring mucoid strains at the expense of non-mucoid strains in the respiratory tract of cystic fibrosis patients.