# Marek’s disease virus replication in chicken skin reconstructed in vitro: evidence for viral particles in corneocytes

## TL;DR

Researchers created an in vitro model of chicken skin to study Marek’s disease virus replication and observed viral particles in the outermost skin layer for the first time.

## Contribution

This study introduces a novel in vitro model using chicken skin equivalents to replicate Marek’s disease virus infection and shedding.

## Key findings

- MDV replicates in chicken skin equivalents and localizes to the upper epidermal layers.
- Viral particles were observed in cornified keratinocytes, suggesting possible environmental release.
- Fluorescent vaccine strains of MDV can infect and replicate in the model.

## Abstract

Marek’s disease (MD) is a lethal lymphoma of chickens, which is caused by MD virus (MDV), an alphaherpesvirus. MDV infects epithelial cells of the skin appendages, notably feather follicles, replicates in these cells and is shed into the environment exclusively from these tissues. Here, we tested whether chicken skin equivalents (SEs) can be used to model MDV infection. Primary chicken keratinocytes were seeded on a suspension of fibroblasts in collagen and induced to terminally differentiate at the air-liquid interface. A recombinant MDV expressing the Katushka fluorescent protein (MDV-KAT) was introduced into SEs by seeding primary keratinocytes together with MDV-KAT-infected keratinocytes of the K8 cell line. KAT-mediated fluorescence increased during the culture of infected SEs, indicating virus infection and replication, while the expression of keratinocyte differentiation markers was not significantly altered by MDV infection. MDV did not spread to the dermal compartment of SEs but localized to the upper layers of the epidermis. Viral particles were readily observed by electron microscopy in living keratinocytes and for the first time in cornified keratinocytes of the outermost layer of infected SEs, suggesting that viral elements can be released into the environment. Finally, we demonstrated that two fluorescent vaccine strains of MDV, Rispens and herpesvirus of turkey, can infect and replicate in SEs. Taken together, this study establishes chicken SEs as an in vitro model for essential steps of MDV infection.