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:Our observations, showing increased sIL2R levels during acute exercise, are supported by the results of others (Baum et al. 1994; Dufaux and Order 1989; Sprenger et al. 1992; Tilz et al. 1993); together these findings suggest that elevated receptor levels during exercise could bind IL-2, and hence down-regulate IL-2-dependent cell-mediated immune responses by reducing free circulating IL-2 levels and/or mitogen-stimulated cell proliferation.
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