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:(Ig)–like domains and whose cytoplasmic region contains immunoreceptor tyrosine-based inhibition motifs that mediate the binding and activation of the protein tyrosine phosphatases SHP-1 and SHP-2.(19,20) Tyrosine phosphorylation of SIRPα is triggered by various growth factors and cytokines as well as by integrin-mediated cell adhesion to extracellular matrix proteins.
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