Antigenic variation of Borrelia turicatae Vsp surface lipoproteins occurs in vitro and generates novel serotypes

As a means of avoiding the host immune response, the tick-borne relapsing f ever spirochete Borrelia turicatae undergoes antigenic variation in its abu ndant surface lipoproteins. In this study, B. turicatae strain Oz1, serotyp e B, was subcultured in vitro and cloned by limited dilutions after 50 pass ages. Four different serotypes (serotypes A, B, E, and F) differing by thei r expressed Vsp lipoproteins were isolated. Using pulsed-field gel electrop horesis, we showed that the variability in surface-exposed proteins is corr elated with rearrangement between different linear plasmids, defining serot ype-specific plasmid profiles. Moreover we determined the nucleotide sequen ce of genes encoding the VspE and VspF lipoproteins, corresponding to the t wo novel serotypes E and F, respectively. Our results showed that antigenic variation in B. turicatae occurs spontaneously in vitro, in the absence of immune selection. (C) 2000 Editions scientifiques et medicales Elsevier SA S.