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:Resistance to TB involves macrophages [2,4], dendritic cells (DC) [17,18], and T cells [18], and multiple studies in humans and mice have shown that maintenance of TB latency requires a Th1 T cell immune response and IFN-c, which is a signature cytokine of this response.
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