Dermal inflammation elicited by synthetic analogs of Treponema pallidum and Borrelia burgdorferi lipoproteins

The membrane lipoproteins of Treponema pallidum and Borrelia burgdorferi have potent immunostimulatory properties in vitro, implicating them as major inflammatory mediators in syphilis and Lyme disease. Recently, we reported that synthetic lipohexapeptide analogs (lipopeptides) of the lipoproteins could be used as surrogates for native spirochetal lipoproteins in immune cell activation studies in vitro. The present study was designed to evaluate the inflammatory properties of the lipopeptides in vivo and to correlate the cellular responses to these synthetic analogs with the histopathology of syphilis and Lyme disease. Lipopeptides corresponding to the 47-kDa major membrane lipoprotein of T. pallidum and the outer surface protein A of B. burgdorferi injected intradermally induced dose-dependent dermal inflammation in mice; the initial predominantly neutrophilic (mice) or heterophilic (rabbits) cellular infiltrates were followed by infiltrates consisting predominantly of mononuclear cells. The intradermal response of rabbits to the 47-kDa lipopeptide was strikingly similar to that observed for animals infected intradermally with T. pallidum. In all cases, lipopolysaccharide was substantially more potent as an inflammatory mediator than the spirochetal lipopeptides. In contrast to the lipopeptides, nonacylated hexapeptides elicited minimal or no dermal lesions in mice or rabbits, underscoring the importance of acyl modification to the inflammatory properties of the lipopeptides. This study provides the first in vivo evidence that the spirochetal lipoproteins/lipopeptides contribute to the immunopathogenesis of syphilis and Lyme disease.