RESUMEN
Objective To screen out specific aldosterone(ALD)antibodies using phage display technology and recom-binant antibody technology,providing raw materials for the research and development of ALD diagnostic kits.Methods Five healthy and clean New Zealand white rabbits were selected and immunized for the first time against the diluted ALD-keyhole limpet hemocyanin antigen(2 mg·L-1)using a multi-point injection method on the back,with a dose of 1 mg per rabbit.Immunization was administered again every 2 weeks,with a 50％reduction in dose.Starting from the third immunization,the ear vein blood of the rabbits was collected one week after each immunization.A chemiluminescent plate coated with 0.25 mg·L-1 ALD-bovine serum albumin antigen was used to measure serum titers via indirect and competitive methods.After the 5th immunization,the rabbit with high serum titers and good specificity was selected,and its spleen and bone marrow were removed.The spleen tissue was grinded,and RNA was extracted using TRIzol reagent in one step to obtain gene sequences in the variable region of light chain(VL)and the variable region of heavy chain(VH).The single-chain variable fragment(ScFv)was connected through the linker and constructed into the bacteriophage vector Pcomb3xss;then,it was carried to Escherichia coli TG1 through electrotransformation,and the ALD ScFv phage display library was constructed accordingly.Three to five rounds of enrichment screening were performed against the library.Monoclonal clones,identified by enzyme-linked immunosorbent assay(ELISA)competitive method,were selected for phage supernatant preparation,and a highly competitive clone sequence was obtained.The screened clone sequence was inserted into the pCMV3 expression vector,and the HEK293 cell was transfected using the transient transfection method after the plasmid was extracted.One week later,the supernatant was collected,and its purity and expression were identified by affinity chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE).Results After the 5th immunization,the serum titers of 5 rabbits were indirectly tested,and the results showed that the serum titers of 4# and 5# white rabbits were still greater than 10,000 after being diluted by 32,000 times.The test results based on the competitive method showed that the ratio of low to high values in the plasma sample of 5#white rabbit was 2∶1,superior to that of other white rabbits.The 5# white rabbit was selected for phage library construction.The VL and VH gene fragments were amplified by conventional polymerase chain reaction,and then bridged into ScFv(VL+VH).The agar gel electrophoresis analysis showed that the size of the band was about 750 bp,which was consistent with the size of the originally designed fragment.ScFv was cleaved and electroporated into Escherichia coli TG1 to construct a phage library with a storage capacity of 4.73 × 108 cfu·mL-1.After 3 rounds of washing,300 monoclonal clones were selected from the outbound petri dishes to prepare monoclonal bacteriophages.The ELISA results showed a positive rate of 100％among the 300 clones,and 42 clones were tested positive for calibration competition,with a screening rate of 14％.The 42 positive clones were further subjected to clinical sample competition testing,and 16 monoclonal strains that met the requirements were screened.The 16 strains were retested,and the results of the two tests were consistent.After sequencing,6 antibody sequences were selected for construction and expression.After purification,SDS-PAGE reduced gel electrophoresis results showed that there were bands at positions 50,000 on the heavy chain and 25,000 on the light chain.Six highly affinitive and competitive rabbit ALD monoclonal antibodies were obtained.Conclusion Six highly affinitive and competitive rabbit ALD antibodies are successfully screened using phage display technology,which provides a reference method for the discovery of small molecule antibodies.The screened AD1 85 and AD277 antibodies show a competitive advantage twice that of the positive control in the competition of calibration and clinical samples,providing a possibility for the development of raw materials for ALD detection kits.