VARIABLE MAJOR PROTEINS OF BORRELIA-HERMSII

B. hermsii, a relapsing fever agent, manifests antigenic variation in vivo and in vitro. Three mouse-passaged serotypes of strain HS1 (7, 14 and 21) and a HS1 derivative obtained after multiple in vitro passages (C serotype) were studied. All 4 serotypes had 2 major proteins in whole cell lysates fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. One major protein species (pH) had the same apparent subunit MW (.apprx. 3.9 .times. 104) in all the serotypes. The other abundant protein in lysates, pI, had a different apparent MW in each serotype. In 1 gel the MW of pIc, pI7, pI14 and pI21 were 1.9, 4.2, 4.1 and 4.0 .times. 104, respectively. Serotype-specific mouse antisera bound to both hemologous and heterologous pII, to homologous pI, but not to heterologous pI in Western blots. Hybridomas were raised from spleens of mice infected with B. hermsii. Monoclonal antibodies were identified by immunofluorescence assays using whole organisms. Monoclonal antibodies specific for serotype 7 (II1826) or for serotype 21 (II3326) bound only to pI7, or pI21, respectively, in Western blots. The surface location of the pI was suggested not only by the immunofluorescence studies, but also by the labeling of pI7 and pI21 when whole cells of serotypes 7 and 21 were incubated with 125I in the presence of iodogen. Under the same circumstances, pII was relatively poorly labeled. These studies have identified the variable pI proteins of B. hermsii as serotype-specific antigens. A change from one pI to another may be the basis of antigenic variation of Borrelia species during relapsing fever.