Platelet 3H-serotonin releasing immune complexes induced by Pseudomonas aeruginosa in cystic fibrosis

In vitro formation of immune complexes was studied by 3H-serotonin release from human platelets by P. aeruginosa antigens in the presence of serum from 22 cystic fibrosis patients, chronically infected with mucoid P. aeruginosa (CF + P) and with a pronounced antibody response against these bacteria, and in 24 patients without P. aeruginosa (CF-P). All CF + P patients responded with 3H-serotonin release (16-34%), whereas CF - P patients released less than 15%. In group of CF + P patients the number of P. aeruginosa precipitins was correlated to the serotonin titer. Time courses indicated that 3H-serotonin release was maximal between 2 and 5 min, and that no further release was observed up to 20 min. There was a gradual increase in 3H-serotonin release with higher platelet concentrations. The response was not changed by complement inactivation, and fractionation of serum demonstrated that the serotonin release was dependent on the presence of the immunoglobulin fraction. These experiments support the suggestion of a type III reaction being involved in the lung damage in CF + P patients and also suggest a possible involvement of serotonin in he inflammatory reaction during chronic P. aeruginosa lung infection.