Enhanced dendritic cell maturation by the B-chain of Korean mistletoe lectin (KML-B), a novel TLR4 agonist

Korean mistletoe lectin (KML) is composed of A and B sub-chains. The B-chain binds to cell surfaces, whereas the A-chain hinders translation because it is a RIP (ribosome inactivating protein) inducing apoptosis. Although KML has various biological and immunological activities, its potential use in cancer therapy or as an adjuvant therapy is limited by its toxicity to normal cells. This study was conducted to determine whether the B-chain of KML (KML-B) has immunoadjuvant activity and cytotoxicity activity. To evaluate the immunomodulatory activities of B chain KML, in vitro experiments employing bone marrow-derived dendritic cells (BMDCs) were performed. Dendritic cells (DCs) are a unique group of white blood cells that are able to capture and process antigens for presentation to T cells, which constitute primary immune response. In the present study, KML-B was found to be non-cytotoxic to BMDCs. Furthermore, the expressions of co-stimulatory molecules (CD40, CD80, CD86, and MHC II) and the secretions of cytokines (IL-1β, IL-6, IL-12p70, and TNF-α) were increased in BMDCs by KML-B. In addition, other indicators (antigen-uptake and CCR7 expression) of BMDC maturation were changed by KML-B, and the ability of KML-B to enhance various functions by BMDCs was found to be dependent on TLR4 expression. Moreover, BMDCs matured by KML-B induced naive CD4(+) T cell differentiation toward Th1 cells directly and indirectly. These experiments confirm that KML-B exhibits potent immunomodulatory properties and suggest that KML-B be considered a potential dendritic cell-based cancer therapy and immunoadjuvant.