Antigenic Structure and Variation of Herpes Simplex Virus Glycoproteins.

Abstract

The antigenic structure and variability of two major herpes simplex virus type 1 glycoprotein antigens, gB and gC, were examined using virus-neutralizing monoclonal antibodies and a series of antigenic variants selected for resistance to neutralization with monoclonal antibodies. After immunoselection, neutralization-resistant variants were isolated which: (1) failed to express the relevant glycoprotein, (2) expressed reduced amounts of the glycoprotein, (3) secreted truncated forms of the normally membrane-bound glycoprotein, or (4) expressed an antigenically altered, but otherwise normal glycoprotein (monoclonal antibody resistant, mar mutants). Epitopes on gB and gC were operationally defined, and grouped into antigenic sites by evaluating the patterns of reactivity of the mar mutants with panels of monoclonal antibodies. Five nonoverlapping epitopes were identified on gB. The mutation affecting one of these epitopes was mapped to the gB structural gene by marker rescue analysis. Nine epitopes on gC were identified which were clustered in two distinct, complex antigenic sites composed of multiple overlapping epitopes. These two sites were sequentially and topographically separate as shown by competitive binding assays and reactivity of monoclonal antibodies with polypeptide fragments. Antigenic variants with multiple epitope changes in gB and which were gC('-) were constructed by recombination and sequential antibody selection. These variants did not exhibit decreased reactivity with polyclonal antisera. Antigenic variation in gB, which is essential for virus growth, was associated with defects in gB processing and function. Variation in either of two distinct epitopes on gB resulted in partial temperature-sensitive defects in the glycosylation of gB without affecting the function of the glycoprotein. Antigenic variation in both epitopes produced a total defect however, and a loss of function as detected by lack of virus growth at elevated temperature. These two epitopes were conserved between the two serotypes of the virus. These data suggest that the two epitopes lie within functionally essential domains of glycoprotein gB, and that antigenic variation in these epitopes may be constrained since it would compromise virus growth.