Monocyte chemotactic factor in rheumatoid arthritis synovial tissue - Probably a cross-linked derivative of S19 ribosomal protein

The extracts of rheumatoid arthritis synovial lesions from seven patients possessed a strong chemotactic activity for monocytes and a negligible one for polymorphonuclear leukocytes. These results are consistent with a prominent histological feature of the synovial lesion, the mononuclear cell predominant infiltration. The major monocyte chemotactic factor in the synovial tissue extracts was purified to a single protein peak in reverse phase high performance liquid chromatography with a C4 column. NH2-terminal amino acid analysis of the initial 20 residues yielded a single sequence. Surprisingly, this sequence was completely identical to that of S19 ribosomal protein. The purified sample demonstrated two protein bands in SDS-polyacrylamide gel electrophoresis with apparent molecular masses of 34 and 68 kDa. These sizes were 2 and 4 times that of S19 ribosomal protein, suggesting that the chemotactic factor would be a dimer or tetramer of S19 ribosomal protein cross-linked by factor XIIIa. A recombinant human S19 ribosomal protein was prepared as a fusion protein with a maltose binding protein in Escherichia coli. After treatment with factor XIIIa, cross-linked recombinant S19 ribosomal protein exhibited the monocyte chemotactic activity, although the untreated recombinant protein did not.