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:These results are consistent with previous studies in microglia (Bianco et al. 2005), astrocytes (Bianco et al. 2009) and PC12 cells (Cocucci et al. 2007), where ATP stimulation induced the shedding of membrane vesicles of heterogeneous diameter.
Category: