BACKGROUND : Influenza infection is a major public health threat. The role of influenza A virus-induced inflammatory
response in severe cases of this disease is widely recognized. Drug resistance and side effects of chemical treatments
have been observed, resulting in increased interest in alternative use of herbal medications for prophylaxis against this
The South African medicinal plant, Rapanea melanophloeos (RM) (L.) Mez of the family Myrsinaceae was selected owing
to its traditional use for the treatment of several diseases such as respiratory ailments and also previous preliminary
studies of anti-influenza activity of its methanolic extract. The aim of this study was to investigate the immunomodulatory
properties of a glycoside flavone isolated from RM against influenza A virus.
METHODS : The non-cytotoxic concentration of the quercetin-3-O-α-L-rhamnopyranoside (Q3R) was determined by MTT
assay and tested for activity against influenza A virus (IAV) in simultaneous, pre-penetration and post-penetration
combination treatments over 1 h incubation on MDCK cells. The virus titer and viral load targeting NP and M2 viral
genes were determined using HA and qPCR, respectively. TNF-α and IL-27 as pro- and anti-inflammatory cytokines
were measured at RNA and protein levels by qPCR and ELISA, respectively.
RESULTS : Quercetin-3-O-α-L-rhamnopyranoside at 150 μg/ml decreased the viral titer by 6 logs (p < 0.01) in the
simultaneous procedure. The NP and M2 genes copy numbers as viral target genes, calculated based on the
Ct values and standard formula, significantly decreased in simultaneous treatment (p < 0.01). The expression of
cytokines was also considerably affected by the compound treatment.
CONCLUSIONS : This is the first report of quercetin-3-O-α-L-rhamnopyranoside from RM and its immunomodulatory
properties against influenza A virus. Further research will focus on detecting the specific mechanism of virus-host
Additional file 1: Figure S1. 1H NMR spectrum of quercetin-3-O-α-Lrhamnopyranoside
Additional file 2: Figure S2. 13C NMR spectrum of quercetin-3-O-α-Lrhamnopyranoside
Additional file 3: Figure S3. HSQC spectrum of quercetin-3-O-α-Lrhamnopyranoside
Additional file 4: Figure S4. HMBC spectrum of quercetin-3-O-α-Lrhamnopyranoside
Additional file 5: Figure S5. H:H COSY spectrum of quercetin-3-O-α-Lrhamnopyranoside