HSV 1 and 2 are important human viruses, producing primary and reactivation infections; the latter occurs despite intact immunity. This proposal addresses virus and immune interactions which help explain how HSV evades the immune response. HSV glycoproteins, gC, gE and possibly gI reduce the effectiveness of antibody- and complement (C')-mediated virus clearance; gC by binding C' component C3b, and gE/gI by binding the Fc end of IgG. Our goals are: 1) to examine the structural basis for interactions between gC and C3b. We will use linker insertion and site-directed mutagenesis, transfection assays, and biochemical approaches to define gC binding sites. In particular, region III on gC will be analyzed since it is involved in C3b binding, has similarities to human C' receptors such as CR1, and is conserved among gC homologs. Purified gCl and gC2 bind C3b, and protect cell free virus from C'-mediated neutralization. However, on infected cells, only gC1 binds C3b, inhibiting C' lysis. gCl/gC2 intertypic recombinant viruses, and chimeric gCl/gC2 proteins will be used to explore differences between gC1 and gC2. 2) We will evaluate biologic functions of gC in vivo. Mutant viruses which are unable to bind C3b, will be compared with wild type strains for virulence in guinea pigs. Severity of lesions, establishment of latency, and frequency of recurrences will be analyzed. Binding C3b to gC on infected cells triggers changes in cell morphology. We will explore the cellular events involved, and monitor for cell injury. In stably transfected cells, expression of gC1 leads to syncytia. We will determine if gC1 is a fusion protein, and analyze domains involved. 3) We will define the glycoproteins which comprise the HSV Fc receptor (FcR) and determine whether more than one FcR is present. Anti-HSV IgG binds to infected cells in a bipolar fashion; the Fab end binds to an antigenic target and the Fc end binds to the FcR. We will ask if bipolar binding modifies effector functions mediated by the Fc domain of IgG, including antibody-dependent cellular cytotoxicity and C' activation. We will examine cells from infected patients to determine if HSV 1 and 2 induce C3b and Fc receptors in vivo. Defining how HSV glycoproteins favor virus survival will help clarify the complex interactions between HSV and its host.
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