COMPARISON OF THE RATE OF SEQUENCE VARIATION IN THE HYPERVARIABLE REGION OF E2 NS1 REGION OF HEPATITIS-C VIRUS IN NORMAL AND HYPOGAMMAGLOBULINEMIC PATIENTS/

The hypervariable region (HVR) of the E2/NS1 region of hepatitis C vir us (HCV) varies greatly between viral isolates with high rates of geno mic change reported during the course of chronic infection. The HVR is thought to encode a structurally unconstrained ent elope protein cont aining several linear B cell epitopes recognized by neutralizing antib ody. It has been postulated that amino acid changes in the HVR could r esult from humoral immune pressure leading to the selection of escape mutants. The aim of this study was to compare the rates of nucleotide and amino acid variation in the HVR of control patients to patients wi th common variable immunodeficiency (CVID) where the effect of the hum oral immune system is reduced, Five controls and four patients with CV ID were studied, Serum samples were taken over periods of between 1 an d 6 years, HCV was detected by polymerase chain reaction (PCR) with pr imers derived from conserved flanking regions of the HVR. PCR products were cloned into a plasmid vector and recombinant clones identified b y restriction enzyme digestion. Purified DNA from at least three indiv idual clones from each time point was sequenced by the dideoxynucleoti de chain-termination method. Consensus sequences were extracted from t he three clones, and the DNA and deduced protein sequences were compar ed. Control patients had a mean rate of nucleotide change of 6.954 nuc leotide substitutions per year, compared with patients with CVID with a rate of 0.415 nucleotide substitutions per year (P <.02), The corres ponding rates for amino acid variation were 3.868 amino acid substitut ions per year for the control patients compared with 0.185 amino acid substitutions per year for the patients with CVID. These findings sugg est that in the absence of humoral immune selective pressure, the freq uency of occurrence of genetic variation in the major viral species is reduced. The mutations occur, but in the absence of immune selection remain as minor species, The evolution of viral mutants capable of eva ding the host's immune system may contribute to the ability of HCV to establish chronic infection.