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:The CD4+ T cells stimulated with the weak or strong IL-2 protocol, described above, were left uninfected or were infected with 200 ng each of HIV1NL-E and HIV-1NLAD8-D per 1610 6 cells for 2 h, extensively washed, and cultivated in 48-well tissue culture plates (16106 per well) in 10% FBS-RPMI containing IL-2.
Category: