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:and 5% HCF (Origen hybridoma cloning factor, TEBU, Frankfurt/M, Germany) in order to test the culture supernatants for antibody response in ELISA.(29) The culture supernatant from the C3H/J splenocytes used for RNA extraction indicated the presence of TF-binding antibodies, whereas the supernatants from the other mice were negative (data not shown).
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