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:1, CD62L, CD44, Streptavidin (BD Biosciences), Gr-1 (in house), and a conjugate of NP to phycoerythrein, made as described (28), were used to identify leukocyte subsets by flow cytometry, with absolute cell numbers determined by live cell count in 0.
Category: