Differential expression of outer surface proteins A and C by individual Borrelia burgdorferi in different genospecies

Previous studies with different Borrelia burgdorferi sensu stricto (s.s.) s trains revealed that temperature as well as cocultivation with tick cells m odulates the expression of outer surface proteins (Osp) A and C. We investi gated the effects of temperature and of interaction with tick cells in cult ure on the expression of OspA and OspC of the B. afzelii clones cPKo97 and cPKo345 in comparison to the B. burgdorferi s.s. strain N40. To follow the dynamics of Osp expression of single borreliae we used indirect immunofluor escence microscopy with double staining of OspA and OspC. Clone PKo345 alwa ys showed expression of only OspA, regardless the conditions it was subject ed to. Sequencing of the ospC gene disclosed a insertion leading to a stop codon after base 222 and inability to produce OspC. In cPKo97 and N40 OspC is down-regulated at lower temperatures and up-regulated at higher temperat ures, which was especially pronounced on cocultivation with tick cells. Bor reliae adherent to tick cells showed greater OspA expression compared to th e nonadherent ones, an indication that OspA might play a role as adhesin fo r tick cells. Interestingly, cPKo97 and N40 displayed different patterns of Osp expression: cPKo97 simultaneously presents OspA and OspC on single bor reliae, while N40 has either OspA or OspC on single cells. Adaptation of Os pC expression in cPKo97 seems to occur by up- or down-regulation of this pr otein on single borreliae, as shown by alternating intensities of OspC expr ession at different temperatures. In contrast, N40 seem to consist of two s ubsets of borreliae one expressing only OspA and the other only OspC, and c hange in temperature results in growth benefit for one of these subtypes. O ur findings indicate that, regarding OspA and OspC expression, response to temperature and cocultivation with tick cells of B. afzelii is comparable t o B. burgodorferi s.s., but the mode of regulation seems phenotypically dif ferent. Further European isolates should be investigated for OspA and OspC regulation, especially in the face of vaccine development for the European situation.