The spirochaetal bacteria Borrelia burgdorferi (Bb) is the tick-horne causative agent of lyme disease, The major membrane immunogens of Bb are outer surface proteins. The lipid component of these lipoproteins is relevant For the immunogenicity of Bb-lipoproteins, To characterize the antigenic properties, the native Lipid component of lipoproteins was isolated and the detailed molecular structure was analyzed, The molecular structure of the lipoprotein-lipid component turned out to be S(propane-2',-3'diol)-3-thio-2-aminopropanic acid (S-glyceryl-cysteine) with one ester-linked fatty acid, one acetyl group, and one N-terminal amide-bound fatty acid. Fatty acid analysis of the lipid component indicated a heterogeneous composition comprising C16:0, C18:0, C18:1, C18:2, and C 20:0, The antigenicity was tested with in vitro bioassays using human blood-derived dendritic cells (DCs) as antigen-presenting cells and autologous Bb-specific T-cells, We found that human DCs present the lipid component of Bb-lipoproteins via MHC class II inducing an antigen-specific T-cell immune response in vitro.