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:…that were negative for both DAF and CD59 (a PNH phenotype), which are known as reliable indicators of a favourable response to IST in AA (Sugimori et al, 2006), were detectable by our flow cytometry 5 months after the first appearance of NKG2D ligand-expressing granulocytes in 2004…
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