Phenotypic analysis of outer surface protein C (OspC) of Borrelia burgdorferi sensu lato by monoclonal antibodies: relationship to genospecies and OspA serotype

Abstract

Molecular analyses of the genes encoding OspC, a major immunodominant protein of Borrelia burgdorferi sensu lato, revealed a considerable degree of heterogeneity. In the present study, we investigated whether a similar heterogeneity of the OspC phenotype can be shown by analysis with monoclonal antibodies (MAbs). Thirteen OspC-specific MAbs (L22 MAbs) were produced by immunizing mice with either different combinations of whole-cell antigens or recombinantly expressed OspCs cloned from strains belonging to different Borrelia spp. Ten of them differed in their reactivities with various strains. Western blot (immunoblot) analyses of 38 B. burgdorferi sensu lato strains resulted in 13 different reactivity patterns. These 13 different patterns were observed among only six different OspA serotypes, indicating that OspC is more heterogeneous than OspA. Patterns 1 to 4 were present only in B. burgdorferi sensu stricto, patterns 5 to 7 were present only in Borrelia afzelii, and patterns 9 to 13 were present only in Borrelia garinii. Pattern 8 was observed among B. afzelii and B. garinii strains but not among B. burgdorferi sensu stricto strains. One L22 MAb (2B8) recognized a common OspC-specific epitope of all 38 B. burgdorferi sensu lato strains analyzed, and another one (22C11) recognized a common epitope of OspC from both B. afzelii and B. garinii and was not reactive with OspC from B. burgdorferi sensu stricto. Western blot and sequence analysis of truncated OspCs located the 22C11 epitope as well as a species-specific sequence motif between amino acids 20 and 35. Other broadly reactive L22 MAbs were 10D3, 1F8, and 7G5. Some L22 MAbs (1C3, 1C3, 12E5, 1B11, 1F10, and 6C8) bound to epitopes present only in a few strains. Relapsing fever borreliae (Borrelia hermsii, Borrelia turicatae, and Borrelia duttoni) were nonreactive, with the following exception: three L22 MAbs (2B8, 6C4, and 10C5) recognized an abundantly expressed 20-kDa-range protein of B. turicatae. Because OspC is an immunodominant protein during the early immune response in Lyme borreliosis and has been shown to be effective as a vaccine in an animal model, our findings have important implications for the development of diagnostic reagents as well as vaccine research.