Development of an improved tracheal explant bioassay for the detection of the ciliary dyskinesia factor in cystic fibrosis serum

A tracheal ring explant system, when used with 25% cystic fibrosis (CF) serum, displayed obvious ciliostasis. Hamster, rabbit, and guinea pig explants all had measurable decreases in ciliary activity after 24 hr of incubation in the serum. The differential response to CF serum (relative to normal serum) was greatly increased by using explants which were maintained 24-72 hr in minimal essential medium (MEM) with 10% horse serum and which were selected on the basis of optimal ciliary activity and vigor. With such a bioassay system of guinea pig tracheal explants, incubation with 25% normal serum would produce essentially no change in relative ciliary activity (score of 242 of a possible 300), whereas CF serum resulted in an 86% decrease (score of 33). Scanning electron microscopic observation indicated that the explants displaying the CF-ciliostatic effect had significant accumulations of mucous over the ciliated epithelial surface. A biochemical viability assay (dehydrogenase activity) showed no cytonecrosis when CF serum-treated tissues were compared to standard explants (10% horse serum in MEM) or control explants (25% normal human serum).