Generation of a recombinant collagen type II peptide library. (A) Amino acid sequences of the inserted collagen type II (CII) sequences into the GPP-Foldon scaffold and the corresponding peptide numbers (1 to 71). Underlined letters correspond to known B-cell and T-cell epitopes followed with their names in brackets. The control peptide (rCII-71) lacks the CII insert but includes the Foldon trimerization domain and GPP10. (B) Sodium dodecyl sulfate polyacrylamide gel electrophoresis showing protein bands at 25 kDa for all 71 rCII peptides. (C) Enzyme-linked immunosorbent assay confirming monoclonal antibody recognition to four of the immunodominant rCII peptides (122:41 specific for rCII-13, CIIC1 specific for rCII-28, the UL1 antibody specific for rCII-37, M2139 recognizing rCII-41) and testing of the monoclonal antibody mix to the control peptide rCII-71. (D) Monoclonal antibody CIIC1 binds to triple-helical but not heat-denatured rCII-28 peptides and rat CII. rCII, recombinant collagen type II.