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Antigenic variation (mar mutations) in herpes simplex virus glycoprotein B can induce temperature-dependent
Abstract:
Monoclonal antibody-resistant (mar) mutants altered in the antigenic structure of glycoprotein B (gB) of herpes simplex virus type 1, strain KOS-321, were selected by neutralization with each of six independently derived gB-specific monoclonal antibodies. Analysis of the reactivity patterns of these mar mutants with a panel of 16 virus-neutralizing monoclonal antibodies identified at least five nonoverlapping epitopes on this antigen, designated groups I through V. Multiple mar mutations were also introduced into the gB structural gene by recombination and sequential antibody selection to produce a set of mar mutants with double, triple, and quadruple epitope alterations. Group II (B2) and group III (B4) antibodies were used to select the corresponding mutants, mar B2.1 and mar B4.1, which in addition to carrying the mar phenotype were temperature sensitive (ts) for processing of the major partially glycosylated precursor of gB, pgB (Mr = 107,000), to mature gB (Mr = 126,000) and showed reduced levels of gB on the cell surface at high temperature (39 degrees C). These mutants were not, however, ts for production of infectious progeny. A recombinant virus, mar B2/4.1, carrying both of these alterations was ts for virus production and failed to produce and transport any detectable mature gB to the cell surface at 39 degrees C. Rather, pgB accumulated in the infected cell. Revertants of the ts phenotype, isolated from virus plaques at 39 degrees C, regained the B2 but not the B4 epitope and were phenotypically indistinguishable from the mar B4.1 parent. Finally, it was shown that group II (B5) and group III (B4) antibodies failed to immunoprecipitate pgB (39 degrees C) produced by ts gB mutants of herpes simplex virus type 1 which were not selected with monoclonal antibodies. Taken together, our findings indicate that (i) mar mutations can alter antigenic as well as other functional domains of gB, namely, the domain(s) involved in processing and infectivity, and (ii) group II and group III epitopes lie within an essential functional domain of gB which is a target for ts gB mutations.
Insights
Monoclonal antibody-resistant mutants reveal new functional domains on herpes simplex virus type 1 glycoprotein B. These findings show that mutations affecting viral antigenicity also impact glycoprotein B processing and infectivity.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is crucial for viral entry and is a target for neutralizing antibodies.
- Monoclonal antibodies (mAbs) are valuable tools for dissecting viral protein structure and function.
Purpose of the Study:
- To characterize monoclonal antibody-resistant (mar) mutants of HSV-1 gB.
- To identify distinct antigenic epitopes on gB.
- To investigate the functional consequences of mutations within these epitopes, particularly concerning gB processing and infectivity.
Main Methods:
- Selection of mar mutants using gB-specific mAbs.
- Analysis of mutant reactivity with a panel of neutralizing mAbs to map epitopes.
- Introduction of multiple mar mutations via recombination and sequential selection.
- Assessment of temperature sensitivity (ts) for gB processing and cell surface expression.
- Analysis of viral infectivity and progeny production.
Main Results:
- At least five nonoverlapping epitopes (groups I-V) were identified on HSV-1 gB.
- Mutants with alterations in group II and group III epitopes exhibited temperature-sensitive defects in gB precursor processing and reduced cell surface gB levels at high temperatures.
- A double mutant (mar B2/4.1) showed a severe defect in gB transport and processing, leading to temperature-sensitive viral production.
- Revertants regained specific epitopes, indicating the genetic basis of the observed phenotypes.
Conclusions:
- Monoclonal antibody resistance mutations can alter not only antigenic sites but also functional domains of gB involved in processing and infectivity.
- Epitopes targeted by group II and group III antibodies are located within essential functional regions of gB.
- These regions are susceptible to mutations that confer temperature sensitivity, impacting gB maturation and cell surface transport.