Syner gistic cytokine production by murine dendritic cells in response to their simul-taneous activation with pairs of agonists of different innate immune receptors

The phenomenon of super-additive (synergistic) cytokine production by murine dendritic cells in response to their simultaneous activation with pairs of agonists of different innate immune receptors was studied. Paired combinations of TLR4, TLR9 and NOD2 agonists, each used in a wide range of concentrations (from 0.05 to 5 μg/ml), were examined. Synergistic production of cytokines was represented as a synergy factor (SF), calculated as the ratio of response induced by certain pair of agonists to a sum of response rates induced by each of these two agonists, used alone. According to production of IL-12 by dendritic cells, maximum SF were observed after activation with TLR4 + NOD2 (SF = 12.8), and TLR4 + TLR9 (SF = 7.1), and TLR9 + NOD2 (SF = 5.8) agonists combinations. In all, the synergism was mostly observed when low concentrations (0.05-0.5 μg/ml) of agonists were used. All pairs of agonists studied also gave considerable synergy in induction of MIP-1α, showing SF 4.5, 4.8 and 2.9 with TLR4 + NOD2, or TLR4 + TLR9, or TLR9 + NOD2 agonists combinations, respectively. A synergism was less prominent in production of TNF-α (SF = 1.3) and MCP-1 (SF = 2.8). Just additive, but not synergistic productions were observed as regards to RANTES and IL-1, when dendritic cells were activated using the pairs of TLR4, TLR9 and NOD2 agonists.