Previous study revealed that a specific lignin-carbohydrate preparation, named as lignin-rich enzyme lignin (LREL) derived from plant husk, is a novel toll-like receptor 4 ligand and shows a potent immune-stimulatory activity against dendritic cells (DCs) in vitro. In this report, we investigated immune-stimulatory activity of LREL in vivo. Single intraperitoneal (i.p.) or oral treatment of LREL elicited activation of systemic and mucosal DCs, which were accompanied by significant elevation of cell surface activation markers and ratio of IL-12p40 producing cells. In addition, LREL-fed mice showed not only mucosal DCs activation but also significant increase of IFN-γ⁺ CD4⁺ T cells in mesenteric lymph node (MLN), respectively. We further examined the effect of LREL oral immunization in combination with ovalbumin (OVA) on the activation of acquired immune system. In LREL administered group, total mucosal IgA concentration was significantly increased, while antigen-specific immunoglobulin A (IgA) concentration was not changed between groups. On the other hand, both total and antigen-specific IgG concentrations in plasma were significantly increased in the LREL administered group. Taken together, oral treatment of LREL is able to affect mucosal and systemic antibodies induction and might be useful for effective immune-stimulatory functional foods and mucosal vaccine adjuvant.
Keywords: Toll-like receptor 4 (TLR4); dendritic cell; immunoglobulin A (IgA); innate immunity; lignin-carbohydrate; mucosal immunology; vaccine adjuvant.