Biological activities of native and recombinant Borrelia burgdorferi outer surface protein A: dependence on lipid modification

Borrelia burgdorferi lipoproteins are 50- to 500-fold more active as cytokine inducers and B-cell mitogens than Escherichia coli lipoproteins and synthetic peptides containing the tripalmitoyl-S-glyceryl-cysteine moiety. To investigate the source of this unique potency, we compared native OspA from B. burgdorferi with recombinant lipidated OspA produced in E. coli. As little as 10 ng of either protein per ml stimulated B-cell proliferation and production of cytokines and nitric oxide by macrophages. The two proteins induced comparable antibody responses in mice. Nonlipidated OspA made in E. coli had no stimulatory activity. Thus, lipid modification is essential both in vivo and in vitro for the immunological properties of OspA. The lipid moiety appears equally active whether produced in B. burgdorferi or in E. coli.