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:Ligation of SIRPα by CD47 is thought to promote the tyrosine phosphorylation of the cytoplasmic region of SIRPα.(20) We therefore propose that either cis or trans interaction of CD47 with SIRPα on cDCs promotes CD4 cDCs survival in secondary lymphoid organs by inducing the tyrosine phosphorylation of SIRPα.
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