An extract of the fern Polypodium leucotomos (Difur) modulates Th1/Th2 cytokines balance in vitro and appears to exhibit anti-angiogenic activities in vivo: pathogenic relationships and therapeutic implications.

In the present study we show the capacity of an extract of the fern Polypodium leucotomos (PLE) to partially inhibit the production of cytokines showing a Th1 pattern (IL-2, IFN-gamma and TNF-alpha) in human PHA-stimulated peripheral blood mononuclear cells. The percentage of inhibition was 24% for IL-2, 72% for INF-gamma and 53% for TNF-alpha. With regard to Th2 cytokines, the addition of PLE resulted in a significant increase (33%) in IL-10 production. Surprisingly, the production of the inflammatory cytokine IL-6 was completely abolished (100% inhibition) by PLE at all doses tested. In a second experiment in vivo we show that, the topical application of PLE to the skin of hairless albino mice (Skh-1) significantly diminished the mast cell infiltrate as well as the number of blood vessels triggered by chronic ultraviolet B (UVB) irradiation. These data show that PLE moderately inhibits the immunological Th1 responses, thus explaining the immunosuppressive as well as the anti-inflammatory and antioxidant activities reported in other studies carried out with PLE. The clear inhibitory effect on TFN-alpha and IL-6 production strongly suggest that this may be the mechanism by which PLE: (a) inhibits angiogenesis in vivo in the mouse model described here, and (b) prevents Langerhans' cells depletion caused by solar irradiation in humans. Taken together, these data suggest that PLE works through the induction of suppressive/anti-inflammatory cytokines such as IL-10 and/or TGF-beta which in turn appear to allow the partial deactivation of macrophages or other accessory cells. These features suggest that PLE could be useful in the treatment of autoaggressive/inflammatory conditions due to an exacerbation of Th1 responses.