ABSTRACT
Objective To determine the reactivity of occult HBV infection (OBI)-related S-gene mutations to various anti-HBs antibodies (Abs) and HBsAg detection reagents.Methods Nine representative S-gene mutations M1-M9 (including 5 novel mutations M1-M5) from 1 OBI patient and 3 OBI blood donors were investigated.S-gene recombinant plasmids harboring 9 mutants or wild-type sequences constructed before were transfected into Chinese hamster ovary (CHO) cells,respectively.HBsAg expression levels and reactivity with various anti-HBs Abs and regular HBsAg detection reagents of all the mutants were analyzed.Results Compared to wild-type strain,intracellular HBsAg levels of the 9 mutants were obviously reduced upon Roche quantitative Elecsys assay.In contrast,analysis of the same samples using anti-His-tag Ab showed that the levels of HBsAg-Histag fusion protein were significantly reduced only in mutants M1,M6,and M7.The results of reactivity of mutant HBsAg against 6 anti-HBs Abs (S/CO values) showed that poor reactivity was observed for most mutants.Specifically,M1-,M4-,M7-,and M9-produced HBsAg with Ab4,and M9-produced HBsAg with Ab6 had the worst reactivity (S/CO＜1) compared to the wild-type.The results of reactivity of mutant HBsAg with 6 commercial HBsAg detection reagents showed that the reactivity for most mutants was significantly lower than that of the wild-type (P＜0.05).The miss rates of ELISA reagents D,E,and F were 11.1％,22.2％,and 55.6％,respectively.Conclusions Lower-affinity of studied mutant HBsAg with anti-HBs is one of the major causes of OBI presentation.The regular HBsAg detection reagents used currently in clinic show a significant deficiency in detection of the mutant HBsAg and thus need to be improved.