Interactions between Herpes Simplex Virus, intraepidermal nerves and epidermal Langerhans and dendritic cells within human skin

Herpes Simplex virus types 1 and 2 (HSV-1 and -2) are prevalent lifelong infections globally, causing serious complications and predisposing to HIV acquisition. HSV-1 infection of the skin/mucosa initiates a race between the immune response to control and clear the virus and HSV-1 reaching the intraepidermal nerves to infect sensory neurons in order to establish latent infection and evade immune clearance. The aims of this thesis are (1) determine the kinetics of HSV-1 spread to intraepidermal nerves fibres (IENF) as in initial infection and (2) investigate if HSV- 1 spreads from nerves to epidermal dendritic cells (DCs) as in recurrent infection. We examined the density of nerves within the epidermis of human skin and genital mucosa. IENF were identified by immunofluorescence using the marker PGP9.5. There was greater density of IENF in human foreskin and labia compared to abdomen, suggesting that access to nerves by HSV-1 may vary, depending on the site of initial infection. Nerves were found to extend superficially to the stratum corneum. Genital skin explants were used to study the kinetics of initial HSV-1 infection after topical application through microneedle patches. Individual viral particles were identified by DNAscope combined with PGP9.5 labelling. HSV was identified close to IENF and within papillary dermal nerves within 24 hours of infection. To examine the consequences of the intraepidermal nerve-LC interaction, we utilised a compartmentalized neuronal system which separates the cell body and axons of cultured rat dorsal root ganglion neurons and LCs and DCs isolated from epidermal rat skinto observe HSV-1 infected axons interacting directly with LCs and DCs and infection of these cells. Thus, these two experimental systems allowed 1. the study of the kinetics of HSV spread to intraepidermal nerves, and the spread of HSV along axons into LCs/DCs and subsequent functional consequences informing development of future HSV treatments and vaccines