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.
ABSTRACT
HEV is classified into H (human) group and Z (zoonosis) group according to its compatible host. H group contains genotype 1 and genotype 2 HEV isolates which infect human only; Z group contains genotype 3 and genotype 4 HEV isolates which infect both human and animals. After analysis of amino acid sequences between ORF2 aa368 and aa606, four group-conserved sites that were all located in the neutralization region of ORF2 were identified. They are aa483, aa492, aa497 and aa599. Mutation analysis and capture PCR were then performed on these sites with a group of monoclonal antibodies. Results showed that the difference of the aa497 between H and Z groups was responsible for the maintenance of their group-specific immunodominant epitopes, probably through confirmation-dependent epitope changes. Thus, aa497 and its related change on the surface structure of HEV may play important roles in host selection by H and Z groups of HEV.