Identification of fibroblast-derived CXCL10. The relative molecular mass (Mr) of reverse-phase-HPLC-purified CXCL10 was determined by electrospray ion trap mass spectrometry. Results show the (a) averaged and (b) averaged deconvoluted spectra of CXCL10 that eluted in between 26% and 28% acetonitrile from the C8 column (Figure 6). The amino acids cleaved off (one-letter code), explaining the differences between the CXCL10 isoforms, are indicated on top of the averaged deconvoluted spectrum. Both NH2-terminally truncated, COOH-terminally intact CXCL10(3–77), CXCL10(4–77), CXCL10(5–77), CXCL10(6–77), and NH2-terminally and COOH-terminally cleaved CXCL10(3–73), CXCL10(4–73), CXCL10(5–73) and CXCL10(6–73) were identified. The deviation between the theoretical and the experimentally determined average Mr for each amino acid is indicated below the one-letter code.