A comparative evaluation of recombinant Mycobacterium tuberculosis ESAT6-CFP10 and PPD as the antigen ci reagents for skin test in guinea pigs

Abstract

Objective To comparatively evaluate the effects of a recombinant Mtb protein ESAT 6-CFP10 （ rESAT6-CFP10 ） and a purified protein derivative （ PPD ） as skin test reagents in guinea pigs . Methods Guinea pigs were sensitized with different Mycobacteria species .After sensitization , all guinea pigs were intradermally injected with rESAT6-CFP10 and PPD.At 48 h after the injection, the size of ery-thema at injection sites was measured by using a double-blind method .For guinea pigs sensitized with viable Mtb, the size of erythema at injection sites were measured at 24 h after the injection .The positive conversion rates of skin test with rESAT 6-CFP10 and PPD were calculated .Results The results of PPD skin test were positive in all guinea pigs sensitized with viable Mtb , killed Mtb and BCG with erythema diameters of （11.4 ±0.9） mm, （11.8±1.1） mm and （13.2±0.8） mm, respectively.Positive skin test with rESAT6-CFP10 was only observed in guinea pigs infected by viable Mtb-showing erythema diameters of （13.7±5.7） mm. The skin test with rESAT6-CFP10 was negative in guinea pigs sensitized by killed Mtb-and vaccinated by BCG.The skin tests by using rESAT6-CFP10 and PPD were performed on randomly selected guinea pigs at ninth day after infection by Mycobacterium tuberculosis H37Rv.At the 2nd week, totally 24 selected guinea pigs showed positive skin test results with rESAT6-CFP10 （24/24） with erythema diameters of （19.9± 3.0） mm, while only 15 out of 24 had positive PPD skin test with erythema diameters of （6.1±5.5） mm. At the 4th week, all guinea pigs showed positive PPD skin test （3/3） with erythema diameters of （12.7± 2.5） mm.Conclusion The skin test by using recombinant ESAT 6-CFP10 protein can effectively distin-guish viable Mtb infection from BCG vaccination and killed Mtb sensitization , which is a more suitable anti-gen than PPD for the early diagnosis of Mtb infection . Key words: Recombinant protein; Mycobacterium tuberculosis; Guinea pig; Skin test