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:After shear exposure, cell lysates were obtained and ERK activation in the cell lysates (10 μg) was examined by Western blot analysis with the use of an antibody specific to the active, phosphorylated form of ERK (phospho-ERK) (New England Biolabs) as described previously (15).
Category: