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:These results confirmed previously reported observations that intestinal and dermal MHC IIhi F4/80hi macrophages originate from BM monocytes (Bain et al., 2014; Rivollier et al., 2012; Tamoutounour et al., 2013; Zigmond and Jung, 2013).
Category: