In vitro studies of Rickettsia-host cell interactions: Confocal laser scanning microscopy of Rickettsia helvetica-infected eukaryotic cell lines

摘要

The pathogenicity of Rickettsia helvetica has not been investigated in depth to date. In humans, seroprevalences up to 12.5% against R. helvetica have been demonstrated with forest workers being predisposed to infection. However, fulminant clinical cases are rare indicating a rather low pathogenicity compared to other Rickettsia species. We therefore investigated growth characteristics of a R. helvetica tick isolate (AS819) in two different eukaryotic cell lines with focus on ultra-structural changes of host cells during infection as determined by confocal laser scanning microscopy. Further investigations included sequencing of rickA, sca4 and sca2 genes, which have been reported to encode proteins involved in cell-to-cell spread in some rickettsiae. In contrast to what is known from other rickettsiae, R. helvetica did not spread directly from cell to cell by actin-based motility presumably due to a deletion in the predicted Sca2 protein. As Sca2 is needed for virulence our results might indicate less virulence and pathogenicity of R. helvetica isolated from ixodid ticks in Germany.