Dendritic cells (DCs) play a decisive role in the innate and adaptive immune response, as they produce cytokines in response to antigen stimulation and activated T cells. Monocytes were isolated from human Peripheral Blood Mononuclear Cells (PBMCs) and were treated with GM-CSF and IL-4 to derive to MDDCs. Because OspA is known to trigger TLR2-based receptors we stimulated MDDCs with purified proteins in order to access the effect of the naked protein (wildtype OspA ( wt OspA) versus a OspA mutant lacking the leader peptide ( mut OspA)), on cytokine induction. We co-cultured MDDCs with 2.5 mg/ml of purified wt OspA or mut OspA during 48 h and the production of pro-inflammatory cytokines TNFa, IL-12, IFNc, and antiinflammatory cytokine IL-10 was quantified by ELISA (Fig. 5A , 5B, 5C and 5D, respectively). wt OspA induced TNFa and IL-10 production (Fig 5A and 5D ) but it did not induce neither IL-12 nor IFNc ( Fig. 5B and 5C ). Compared to wt OspA, the OspA mutant lacking the leader peptide, mut OspA, showed a 10 fold-decrease in the TNFa production (Fig. 5A ) and a 2 fold-decrease in the IL-10 production (Fig. 5D ). Similarly to wt OspA, mut OspA did not induce neither IL-12 nor IFNc cytokine production ( Fig. 5B and 5C ). Differences between wt OspA and mut OspA are statistically significant (*p,0.001 and **p,0.05).