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:Furthermore, MMP-2 and -9 are expressed and secreted by astrocytes (Gottschall et al., 1995; Muir et al., 2002) and induced in the presence of A (Deb and Gottschall, 1996; Deb et al., 2003).
Category: