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:Because MYCN is inversely correlated with MHC I (8–10), and MHC I is positively correlated with ERAP1 expression in human cell lines of various lineages (13, 14), we looked for expression patterns of MYCN, MHC I heavy chain, ERAP1, and ERAP2 by Western blotting (Fig.
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