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:…with the unfolded protein response (UPR) (Hunter et al., 2002), consistent with the expression of a malfolded, endoplasmic reticulum (ER)–localized protein. o2 and o1 (Nelson et al., 1965) also show an increased UPR, but to a lesser extent than in De-B30, fl2, and Mc (Hunter et al., 2002).
Category: