RESUMO
<p><b>OBJECTIVE</b>To study the effect on anti-respiratory syncytial virus of an active compound (AP3) from a Chinese medicinal herb-Herba patriniae in vitro.</p><p><b>METHODS</b>Active component of herba patriniae (AP3) was extracted and its anti-respiratory syncytial virus (RSV) effect was tested. A water soluble substance (AP3) was isolated from a Chinese herb Herba patriniae, by hot water extraction, ethol precipitation and gel permeation column chromatography. The cytotoxicity of AP3 was tested by adding it to HeLa cells directly. Its effect against RSV was estimated by CPEI assay while ribavirin was used as positive control.</p><p><b>RESULTS</b>Chemical test showed that the nature of substance AP3 was polysaccharide. The median cytotoxic concentration (TC(50)) of AP3 was 11.45 mg/ml by morphological observation and the median effective concentration (50% effective concentration, EC(50)) of it against replication of the long strain of RSV in HeLa cells was 0.0986 mg/ml. The Therapeutic index (TI = TC(50)/EC(50)) of AP3 was 116.12, much higher than the TI of herba patriniae (AP1) (TI = 59.26) and ribavirin (TI = 53.45). Moreover, AP3 gave a dose-dependent response in inhibiting RSV. In the assay, the effect of AP3 against RSV growth was also tested. In addition, the effect of AP3 on virus growth, AP3 inhibited replication of RSV in HeLa cells, when added at 0 h, 2 h, 4 h after virus infection, were also tested.</p><p><b>CONCLUSION</b>This study suggested that the AP3 exerted an obvious inhibitory effect to RSV in HeLa cell culture. This study furnished a reliable evidence for development of a new antiviral drug.</p>