Abstract: This study is to improve the affinity of scFv-AK404R against VEGFR2. The secondary mutational library was constructed by hydrophilic shuffling in CDR3 region of the heavy chain. VEGFR2-specific screening was performed by phage display technology and the protein of mutants was expressed in periplasm of E.coli HB2151 and purified by affinity chromatography. The affinity constant of scFvs was measured by competitive ELISA, and the structure of scFvs was analyzed by bioinformatics. The result showed that a library with 6.4x10(5) scFv members was established by electro-transformation. Two mutated clones with high absorbance value were isolated after screening. After purification by affinity chromatography, electrophoretically pure scFv proteins were obtained. The competitive ELISA showed that the affinities of WZ01 and WZ02 were three times higher than that of the parental AK404R, and bioinformatics analysis showed that the enlarged contact surface and fitted closely with KDR3 surface may be the reasons for improved affinity. These results suggest that introducing hydrophilic amino acids to the heavy chain CDR3 region is an effective approach to improve the affinity of scFv.

BACKGROUND:With the development of modern pathological techniques, the misdiagnosis rate has been reduced remarkably, but special stains are still the most important method for pathological diagnosis. OBJECTIVE:To compare the advantages and disadvantages of different special stains used for observing the structure of human lumbar facet joints. METHODS:The specimens of facet joint cartilage at L4/5 level were collected from patients undergoing lumbar surgery, and then stained with hematoxylin-eosin, safranin O, toluidine blue, Masson, and saranin-O-fast green for structure observation. RESULTS AND CONCLUSION:The structure of the articular cartilage could be observed clearly through hematoxylin-eosin, toluidine blue, and saranin-O-fast green staining. The cartilage surface, tidemark, and subchondral bone were shown by the hematoxylin-eosin staining, with the presence of violet chondrocyte nuclei. Safranin-O-fast green staining showed the four layers of the cartilage clearly, including the shallow layer (cartilage surface), middle layer (spherical cells arranged in disorder), columnar cell layer (large and multinucleated chondrocytes arranged neatly), tidemark, subchondral bone layer; and the cartilage matrix was reddish uniformly, the subchondral bone was green, and the cartilage and bone tissue showed a striking contrast. The cartilage structure was unclear in toluidine blue staining, with clear nuclei and almost no coloring cytoplasm, but the matrix appeared with slight purplish blue. Safranin O staining showed that the cartilage was red, which had no obvious boundary with the cartilage matrix, and chondrocytes were stained lightly. Masson staining showed clear collagen fibers, but the structures of the cartilage and subchondral were obscure. To conclude, safranin-O-fast green staining can achieve the best results, followed by hematoxylin-eosin staining and Masson staining in turn.