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:Unlike Bcl-2, which is highly expressed in naïve and memory T cells and rapidly downregulated after T cell activation, Mcl-1 expression is strongly induced after TCR stimulation (Dunkle et al., 2011; Opferman et al., 2003).
Category: