Preparation and analysis of immunocompetence of recombinant fusion protein of the immunodominant region in chlamydial protease-like activity factor from Chlamydophila pneumoniae and its application in serodiagnosis

Toclonethegenecodingtheimmunodominantregioninthechlamydialprotease-likeactivityfactor(CPAF)fromChlamydophilapneumoniae,toanalyzeimmunocompetenceoftheexpressedprotein,andtoevaluateitsvalueinserodiagnosis,theCPAFimmunodominantregiongenewasamplified,ligatedintoapGEX6p-2vector,andthentheexpressedrecombinantproteinwaspurifiedwithglutathioneS-transferase(GST)agarosegelFFafterrenaturation,thenidentifiedbySDS-PAGEandWesternblot.AnewindirectELISAwasdevelopedwiththepurifiedproteinascoatingantigen.TheimmunogenicityoftherecombinantproteinwasevaluatedbyimmunizationtoNewZealandrabbits,anditsimmunoreactivitywasanalyzedbyreactingwithanti-C,pneumoniaeantibody.300clinicalserasampleswererespectivelyde-tectedbymicroimmunofluorescence(MIF)asreferencemethodandtheindirectELISA,andthediffer-encebetweenthetwomethodswasanalyzed.Cross-reactivityagainstChlamydiatrachomatiswasinvesti-gatedwiththeindirectELISAtodetectanti-C,trachomatispositiveantisera.Theresultsindicatedthata51.3kDarecombinantproteinwasobtained.Westernblotassayprovedthattherecombinantproteincouldmerelyspecificallyreactwithhumananti-C.pneumoniaeantisera.ThetitersofthespecificIgGan-tibodiesintheimmunizedNewZealandrabbitswereabove1:16000.Anti-C.pneumoniaeIgGpositiveandnegativereferencesereweredetectedwiththeindirectELISA,andtheconcordancerateofnegativeandpositiveresultswereboth100%(40/40).ThesensitivityandspecificityoftheindirectELISAincomparisonwithMIFwere93.8%(45/48)and100%(252/252)separatelybydetecting300clinicalserasamples,andtheconcordanceratebetweenthetwomethodswas99.0%.NocrossreactionagainstC.trachomatiswasfoundwiththeindirectELISAtodetectanti-C,trachomatispositiveantisera.Incon-clusion,thepreparedrecombinantproteinoftheCPAFimmunodominantregionshowsexcellentimmuno-competenceandcanbeusedtodevelopanewindirect