Alpha and gamma interferons inhibit herpes simplex virus type 1 infection and spread in epidermal cells after axonal transmission

Abstract

The ability of alpha interferon (IFN-alpha) and IFN-gamma to inhibit transmission of herpes simplex virus type 1 (HSV-1) from neuronal axon to epidermal cells (ECs), and subsequent spread in these cells was investigated in an in vitro dual-chamber model consisting of human fetal dorsal root ganglia (DRG) innervating autologous skin explants and compared with direct HSV-1 infection of epidermal explants. After axonal transmission from HSV-1-infected DRG neurons, both the number and size of viral cytopathic plaques in ECs was significantly reduced by addition of recombinant IFN-gamma and IFN-alpha to ECs in the outer chamber in a concentration-dependent fashion. Inhibition was maximal when IFNs were added at the same time as the DRG were infected with HSV-1. The mean numbers of plaques were reduced by 52% by IFN-alpha, 36% by IFN-gamma, and by 62% when IFN-alpha and IFN-gamma were combined, and the mean plaque size was reduced by 64, 43, and 72%, respectively. Similar but less-inhibitory effects of both IFNs were observed after direct infection of EC explants, being maximal when IFNs were added simultaneously or 6 h before HSV-1 infection. These results show that both IFN-alpha and IFN-gamma can interfere with HSV-1 infection after axonal transmission and subsequent spread of HSV-1 in ECs by a direct antiviral effect. Therefore, both IFN-alpha and -gamma could contribute to the control of HSV-1 spread and shedding in a similar fashion in recurrent herpetic lesions.

FIG. 1

Diagram of the two-chamber DRG-EC model.

FIG. 2

(a) Effects of increasing concentrations of IFN-α or IFN-γ on inhibition of direct infection of ECs with HSV-1 (MOI = 0.1 TCID₅₀/cell). (b) Effects of different combinations of concentrations of IFN-α and -γ on inhibition of HSV-1 infection of ECs (MOI = 0.1 TCID₅₀/cell). IFNs were added 1 h before HSV-1 infection. IFN-α was used at 500 IU/ml and IFN-γ was used at 300 IU/ml whether alone or in combination. Panels a and b show the results of representative experiments with ECs from a single donor, with each experiment done in triplicate. Similar results were obtained for another five experiments with ECs from five different donors.

FIG. 3

Effect of IFN-γ pretreatment on HSV-1 plaques following direct infection of ECs. (A) Two moderate-sized cytopathic plaques (arrowheads) produced by HSV-1 infection in ECs that were not treated with IFN-γ. Magnification, ×194. (B) Small cytopathic plaque (arrowhead) in ECs treated with IFN-α and -γ. Magnification, ×194.

FIG. 4

(a) Effects of IFN-α, IFN-γ, and control cytokines on the size of cytopathic plaques induced by HSV-1 in ECs after axonal transmission in the DRG-EC model (MOI for HSV inoculum = 0.1 TCID₅₀/neuron). Experimental data presented here are from one experiment with ECs from one donor. (b) Effects of IFN-α, IFN-γ, and control cytokines on the number of cytopathic plaques induced by HSV-1 in ECs after axonal transmission in the DRG-EC model (MOI for HSV-1 inoculum = 0.1 TCID₅₀/neuron). Experimental data presented here are from one experiment with ECs from one donor. The results shown here are representative of those observed for five other experiments with ECs from this donor and two other donors. IFN-a+IFN-g, IFN-α plus IFN-γ.

FIG. 5

(a) Effects of IFN-α, IFN-γ, and control cytokines on the size of cytopathic plaques induced by HSV-1 in ECs after direct infection of the EC monolayers (MOI for HSV-1 inoculum = 0.1 TCID₅₀/EC). Experimental data presented here are from one experiment with ECs from one donor. (b) Effects of IFN-α, IFN-γ, and control cytokines on the number of cytopathic plaques induced by HSV-1 in ECs after direct infection of the EC monolayers (MOI for HSV-1 inoculum = 0.1 TCID₅₀/EC). Experimental data presented here are from one experiment with ECs from one donor. The results shown here are representative of those observed for five other experiments with ECs from this donor and two other donors. IFN-a+IFN-g, IFN-α plus IFN-γ.