We also detected a slight cross-reactivity with S100A12, S100A9 *, and S100A9 on the NP20 spectra after eluting S100A8 (the sequence homologies of the S100A8, S100A9, and S100A12 proteins are around 40%) (32).
Lastly, a comparison within the rheumatic inflammatory disease groups revealed that the S100 proteins weakly distinguished PsA and AS patients, whereas the S100A12 protein was the only variable that significantly distinguished RA patients from PsA patients.
S100 protein peaks were not correlated in PsA or AS patient groups with the CRP, SAA, or log MMP-3 (except for S100A12 in the PsA group) serum concentration, or with clinical variables, including the number of swollen or tender joints and the BASDAI (data not shown).
In this study, we used the SELDI-TOF MS approach to detect S100A8, S100A9, an S100A9 variant (S100A9 *), S100A12, SAA, SAA-R, and SAA-RS, and we identified these proteins by WB, immunodepletion, and nano-LC-MS/MS.
Furthermore, the peak intensities of S100A8, S100A9, S100A9 *, and S100A12, as well as the calprotectin concentration, are correlated with variables that reflect the biological and clinical activity of RA, such as the [DAS.
The recent identification via SELDI-TOF analysis of several truncated forms of S100A8 and S100A12 in cystic fibrosis patients suggests that C-terminal truncations affect protein function (34).