Morphological changes in rat tracheal mucosa immediately after antigen challenge.

We have investigated the morphological effects of an intratracheal challenge with 50 micrograms ovalbumin (OA) on sensitized rat tracheas, in vivo. Female Sprague-Dawley rats were primed ten days before challenge with a single i.t. injection of 100 micrograms OA plus Bordetella pertussis (OA-BP). Two additional groups of animals served as controls: primed animals challenged with saline only and non-primed but OA-challenged animals. Sacrifices--and subsequent morphological studies--were performed prior to and 5, 15 and 60 min after challenge. At each time, the total numbers of epithelial nuclei, subepithelial mast cells (SEMC) and intraepithelial mast cells (IEMC) were scored in six non-adjacent cross sections per trachea. We found that: 1) priming with OA-BP alone did not induce any change in the tracheal mucosa with respect to morphological structure and mast cell counts; 2) no morphological change nor significant modification of the cell counts occurred at any time in tracheas from either of the control groups; 3) in contrast, a luminal heterogeneous exudate and a subepithelial oedema developed in 9 of the 15 tracheas of primed animals within 60 min of OA challenge. In those nine tracheas, the scores of intraepithelial nuclei, of IEMC and of SEMC were found to decrease significantly 15 min after challenge as compared with starting values (p less than 0.05 for each score). The decrease in the number of mucosal mast cells is probably related to the damages of the epithelial cells and to the difficulty with which depleted mast cells can be seen by toluidine blue staining.