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:Phosphorylation of S339CXCR4 correlates with CXCR4 internalization and signaling.(18,40,41) Interestingly, ligation of TCR significantly increased phosphorylation of S339-CXCR4 (Figure 2L-M).
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