Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The antioxidant BHT accumulates predominantly in the lung and induces alveolar epithelial damage because of its action on AEC1 (21), which is followed by the proliferation of pulmonary parenchymal cells resembling human UIP (20,22).
Category: