Varicella zoster virus (VSV) is, by virological standards, one of the most successful human herpesviruses. It infects the great majority of the population in childhood and remains latent in spinal ganglia to reappear as zoster in aging populations. While VZV spreads readily and efficiently in its human host, it is still, despite much effort on the part of virologists, difficult to handle in the laboratory. It is the first human herpesvirus for which a live-attenuated vaccine strain (Oka) has been licensed in the U.S., but the characteristics of Oka which make it suitable for use as a vaccine are not understood. In this proposal, we plan to address several aspects of VZV gene expression (particularly that of glycoproteins) in the context both of virus development (or lack of it) in the infected cell and of the host's immune responses to infection with wild-type and with vaccine virus. There are five specific aims. In the first of these, we expand on work carried out in the previous granting period, proposing to develop monoclonal antibodies against gpV as a means of mapping antigenic sites on this virus-neutralising polypeptide. In aim 2, we will clone glycoproteins gpII and gpIII into vaccinia expression systems. These, along with proteins already cloned (gpV, gpIV, gpI, major capsid protein, major immediate early protein) will be used in immunological assays (humoral and cell-mediated) as well as in protection studies using guinea pig models of VZV infection. Next, null mutants in those glycoproteins (gpV, gpIV, gpI) which we know or strongly suspect to be inessential for growth in cell culture will be constructed; animal model studies will then be pursued with both single and multiple variants. In the fourth aim, the reagents generated above will be used to investigate the nature and kinetics of association of gpV within infected cell membranes and its quaternary relationship to other VZV glycoproteins. Aim five focusses on our observation that the Oka strain of VZV is markedly deficient in the expression of gpV; we should like to define this lesion and attempt to correlate it to the relatively avirulent behavior of the Oka vaccine strain in vivo.