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:This transmembrane protein is mainly concentrated in tricellular tight junctions (tTJ) in the epithelial cells of all tissues, including cochlear supporting cells, hair cells and marginal cells of stria vascularis, and also weakly present in bicellular tight junctions (bTJ) [5, 6].
Category: