The remodelled tracheal basement membrane zone of infant rhesus monkeys after 6 months of recovery

Background In previous studies, we showed that repeated exposure to (1) house dust mite allergen (HDMA) (Dermatophagoides farinae) caused thickening of the basement membrane zone (BMZ) and (2) HDMA+ozone (O-3) caused depletion of BMZ perlecan and atypical development of BMZ collagen (irregular thin areas < 2.0 μm in width). Objective The purpose of this study was to determine if these remodelling changes were reversible after 6 months of recovery. Methods Rhesus monkeys were exposed to a regimen of HDMA and or O-3 or filtered air (FA) for 6 months. After the exposure protocol was completed FA and O-3 groups were allowed to recover in FA for 6 months. The HDMA and HDMA+O-3 exposure groups recovered in a modified environment. They were re-exposed to HDMA aerosol for 2 h at monthly intervals during recovery in order to maintain sensitization for pulmonary function testing. To detect structural changes in the BMZ, collagen I and perlecan immunoreactivity were measured and compared to data from the previous papers. Results The remodelled HDMA group had a significantly thicker BMZ and after 6 months of recovery the width had not regressed. In the remodelled BMZ of the HDMA+O-3 group, perlecan had returned to the BMZ after 6 months of the recovery protocol, and the thin, irregular, collagen BMZ had been resolved. Conclusion In summary, this study has shown that: (1) The width of the remodelled HDMA BMZ did not regress during a recovery protocol that included a sensitizing dose of HDMA. (2) The atypical collagen BMZ in the HDMA+O-3 BMZ was resolved in the absence of O-3. (3) Depletion of perlecan from the BMZ by O-3 was reversed by recovery in the absence Of O-3.