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:…by the release of SPEs and other antigens, which function as superantigens (Proft et al., 2003; Marrack and Kappler, 1990; Talkington et al., 1993; Baxter and McChesney, 2000; Eriksson et al., 1999; Darenberg et al., 2004; Norrby-Teglund et al., 2005; Zurawski et al., 1998; Ekelund et al., 2005).
Category: