43151 Keratinocyte Differentiation State is a Key Determinant of Viral Susceptibility

The epidermis, and keratinocytes (KC) in particular, are important for skin immunity. To identify which epidermal layer is most susceptible to viral infection, we utilized an immortalized KC line that differentiates in the presence of high calcium and a replication-competent, fluorescently-tagged herpes simplex virus (HSV)-1. Human KC were infected with HSV-1 at different stages of differentiation: undifferentiated (low calcium), at the initiation of differentiation (high calcium), and at 24-hour intervals post-differentiation (high calcium). Three days later, infection and replication were quantified via fluorescent imaging. Cytopathic effect was quantified by viral plaques and monolayer clearance. KC infected at the initiation of differentiation showed significantly (p<0.01) increased fluorescence (n=6) and monolayer clearance (n=7) relative to undifferentiated cells or cells differentiated for ≥ 24 hours. This suggests that KC are most susceptible to viral infection during the first 24 hours of differentiation, which is analogous to KC in the lower stratum spinosum. To determine if these findings held true in vivo, we evaluated the histopathology of 6 HSV and 12 varicella zoster virus (VZV) skin lesions. In sections where the edge of the viral immunoreactivity was visible, 100% of VZV (5/5) and 66% of HSV (4/6) cases had viral staining between the stratum basale and granulosum. Collectively, these data suggest that KC that have differentiated to the stratum spinosum level are particularly susceptible to viral infection. This result has implications for dermatological diseases (i.e. atopic dermatitis, Darier disease) with impaired skin barrier function where viral infections cause significant comorbidities.