Herpes simplex virus type 1 (HSV-1) is an important human pathogen which requires activation of
nuclear factor-kappa B (NFκB) during its replication cycle. The persistent nature of HSV-1
infection, and the emergence of
drug-resistant strains, highlights the importance of research to develop new
antiviral agents.
Toll-like receptors (TLRs) play a prominent role during the early
antiviral response by recognizing viral
nucleic acid and gene products, activating NFκB, and stimulating the production of inflammatory
cytokines. We demonstrate a significant effect on HSV-1 replication in ARPE-19 and Vero cells when
oligonucleotides designed to inhibit TLR9 are added 2h prior to
infection. A greater than 90% reduction in the yield of infectious virus was achieved at
oligonucleotide concentrations of 10-20 μM. TLR9 inhibitory
oligonucleotides prevented expression of essential immediate early herpes gene products as determined by immunofluorescence microscopy and Western blotting. TLR9
oligonucleotides also interfered with viral attachment and entry. A TLR9 inhibitory
oligonucleotide containing five adjacent
guanosine residues (G-ODN) exhibited virucidal activity and inhibited HSV-1 replication when added post-
infection. The
antiviral effect of the TLR9 inhibitory
oligonucleotides did not depend on the presence of
TLR9 protein, suggesting a mechanism of inhibition that is not TLR9 specific. TLR9 inhibitory
oligonucleotides also reduced NFκB activity in nuclear extracts. Studies using these TLR inhibitors in the context of
viral infection should be interpreted with caution.