Oligomeric procyanidins (OPCs) have been shown to have antiviral and immunostimulatory effects. OPCs isolated from non-ripe apple peel were tested for capacity to reduce dengue virus (DENV) titers. Similar to published accounts, OPCs exhibited direct antiviral activity. The possibility of enhanced innate immune protection was also tested by measuring and characterizing gene and protein expression induced by OPCs during DENV infection. Treatment of DENV-infected human PBMCs with OPCs decreased viral titers and affected the expression of critical innate antiviral immune products. OPCs enhanced expression of MXI and IFNB transcripts in high MOI DENV infected PBMC cultures, and phosphorylation of STAT2 in response to recombinant type I IFN (IFN I). During low MOI infection, addition of OPCs increased expression of STAT1 transcripts, MHC I and TNFalpha protein production. Thus, OPCs exhibited innate immune stimulation of cells in DENV-infected cultures and uninfected cells treated with IFN I. While OPCs from a number of sources are known to exhibit antiviral effects, their mechanisms are not precisely defined. The capacity of OPCs to increase sensitivity to IFN I could be broadly applicable to many viral infections and two separate antiviral mechanisms suggest that OPCs may represent a novel, robust antiviral therapy.
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