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:Mammalian Derlin-1 participates in the retrotranslocation of major histocompatibility complex class I protein [21,22], and Derlin-2 and Derlin3, two other human paralogs, have been implicated in ERAD [23].
Category: