Serologic type conversion of a herpes simplex virus type 1 (HSV-1) to an HSV-2 epitope caused by a single amino acid substitution in glycoprotein C

Serologic and genotypic analysis of a series of herpes simplex virus type 1 isolates from two patients with genital herpes

Herpes simplex virus type 1 (HSV-1) has been reported increasingly as a cause of genital herpes, although HSV-1 is usually associated with oro-labial herpes. In the present study, serum specimens and materials for viral isolation were obtained serially from two patients with recrudescent HSV-1 genital infections to study serology and molecular epidemiology. Recurrent episodes, during which HSV-1 was isolated, were followed by an increase in the level of anti-HSV-1 antibody, suggesting a booster effect from re-exposure to viral antigens and the possible usefulness of the variation in the level of anti-HSV-1 antibody to diagnose recurrence. While genotypes of HSV-1 isolates obtained from one patient were different from those from the other patient, genotypes of sequential HSV-1 isolates obtained from the same patient were the same, implying that the recrudescent genital lesions of the two patients could be attributed to endogenous recurrence of a latent virus. Sera from one patient neutralized HSV-1 isolates obtained from the other patient as well as HSV-1 isolates obtained from the same patient. An HSV-1 isolate obtained during a later episode in one patient was neutralized by sera taken before/during the later episode of the same patient, as effectively as an HSV-1 isolate obtained during an earlier episode in the same patient; thus, in these two cases, HSV-1 was assumed to have multiplied during recurrence despite the presence of an anti-HSV-1 antibody that could neutralize experimentally HSV-1.

Type-specific reactivity of anti-glycoprotein G antibodies from herpes simplex virus-infected individuals is maintained by single or dual type-specific residues

Glycoprotein G-1 (gG-1) of herpes simplex virus type 1 (HSV-1) and gG-2 of HSV-2 are the only known HSV proteins that induce type-specific human antibody responses. Recently, it was shown that purified human anti-gG-1 and anti-gG-2 antibodies presented a type-specific reactivity to immunogenic stretches with high similarity between gG-1 and gG-2. In this study, the molecular basis for this type-specific recognition was investigated employing synthetic peptides covering the indicated regions, including substitutions of the type-specific residues. The results revealed that single or dual type-specific residues localized within regions of high similarity could induce significant structural differences, explaining the type-specific recognition of the human antibody response to the gG proteins.

Genetic analysis of type-specific antigenic determinants of herpes simplex virus glycoprotein C

Herpes simplex virus type 1 (HSV-1) glycoprotein C (gC-1) elicits a largely serotype-specific immune response directed against previously described determinants designated antigenic sites I and II. To more precisely define these two immunodominant antigenic regions of gC-1 and to determine whether the homologous HSV-2 glycoprotein (gC-2) has similarly situated antigenic determinants, viral recombinants containing gC chimeric genes which join site I and site II of the two serotypes were constructed. The antigenic structure of the hybrid proteins encoded by these chimeric genes was studied by using gC-1- and gC-2-specific monoclonal antibodies (MAbs) in radioimmunoprecipitation, neutralization, and flow cytometry assays. The results of these analyses showed that the reactivity patterns of the MAbs were consistent among the three assays, and on this basis, they could be categorized as recognizing type-specific epitopes within the C-terminal or N-terminal half of gC-1 or gC-2. All MAbs were able to bind to only one or the other of the two hybrid proteins, demonstrating that gC-2, like gC-1, contains at least two antigenic sites located in the two halves of the molecule and that the structures of the antigenic sites in both molecules are independent and rely on limited type-specific regions of the molecule to maintain epitope structure. To fine map amino acid residues which are recognized by site I type-specific MAbs, point mutations were introduced into site I of the gC-1 or gC-2 gene, which resulted in recombinant mutant glycoproteins containing one or several residues from the heterotypic serotype in an otherwise homotypic site I background. The recognition patterns of the MAbs for these mutant molecules demonstrated that (i) single amino acids are responsible for the type-specific nature of individual epitopes and (ii) epitopes are localized to regions of the molecule which contain both shared and unshared amino acids. Taken together, the data described herein established the existence of at least two distinct and structurally independent antigenic sites in gC-1 and gC-2 and identified subtle amino acid sequence differences which contribute to type specificity in antigenic site I of gC.