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:Pneumolysin interaction with TLR4 on epithelial cells induces ERK-mediated production of MUC5A mucin, potentially enhancing trapping of bacteria in mucus and further enabling clearance [99].
Category: