The high-resolution MS/MS spectrum (bottom panel) of the polypeptide indicative for GvHD (Table 3) with the molecular weight of 4.306 kDa. This polypeptide was up-regulated in GvHD samples compared with control samples (Table 1). SwissProt database matching indicated that this is a fragment of collagen α-1 (III) chain (319-366; Homo sapiens) with a calculated mass of 4.306 kDa and a sequence as indicated (top panel). The masses of b-ion fragments (red) and y-ion fragments (blue) are correlated with the obtained sequence using fragment numbers.^28,29