Protein identification using mass spectrometry. (A) A representative MS spectrum (682.3332 m/z) of the peptide from the candidate spot in Figure 4C is shown, which was identified by nanoLC-MS/MS. (B) The deduced sequence is confirmed by MS/MS spectra of b and y ion series as CCL8 peptide (QGMSLCVDPTQK) corresponding to 682.3332 parent ion in panel A. Cysteine is carbamidomethylated in this peptide. (C) Verification of CCL8 as the 8972-Da peak by immunoSELDI is shown. The box highlights the elevation of CCL8 in the GVHD sample but not in the control sample.