Indirubin inhibits inflammatory reactions in delayed-type hypersensitivity

Abstract

Polygonum tinctorium Lour. ( P. tinctorium) is known to have the ability to suppress inflammation. We attempted to isolate the active compounds from P. tinctorium based on their inhibitory effects on the production of interferon-γ, which is a well-known inflammatory cytokine. We thus isolated indirubin, an isomer of indigo. Indirubin exerted its inhibitory effects not only on interferon-γ production by human myelomonocytic HBL-38 cells but also on interferon-γ and interleukin-6 production by murine splenocytes with no influence on the proliferation of either cells. Because of its inhibitory activity on interferon-γ production, we further investigated the effects of indirubin on 2,4,6-trinitro-l-chlorobenzene (TNCB)-induced delayed-type hypersensitivity as a representative inflammatory reaction. When injected intraperitoneally, indirubin significantly inhibited the ear swelling of TNCB-elicited mice. The amount of interferon-γ in the culture supernatants of elicited mouse lymphocytes was inhibited by indirubin treatment. These results suggest that indirubin is a compound with anti-inflammatory effects.