CHI3L1 and Osteoblastoma: In addition, we also tested the interaction of rAY with recombinant protein YKL-40 or YKL-40 secreted from tumour cells in an immunoblotting assay (e.g., an osteoblastoma line MG-63 and a brain tumour line U87) and we found that its specificity was identical to that observed in IHC (data not shown), confirming the high specificity of rAY.