The 120 kDa outer membrane protein of Ehrlichia chaffeensis: preferential expression on dense-core cells and gene expression in Escherichia coli associated with attachment and entry.

The immunodominant 120 kDa protein (p120) of Ehrlichia chaffeensis was demonstrated to be exposed on the surface of purified whole ehrlichial cells examined by immunoelectron microscopy with a rabbit antibody against a portion of the domain containing tandem repeat units. In the intracellular location, the 120 kDa protein was detected by immunoelectron microscopy in the outer membrane of the cell wall of dense-core forms of the ehrlichiae in infected canine macrophage-like cells and as a component of the intramorular fibrillary matrix. No 120 kDa protein was detected in the cell wall of ehrlichial reticulate cells. Recombinant Escherichia coli with a plasmid containing the entire 120 kDa protein gene, but no bacteria with non-recombinant plasmid, attached to the surface of HeLa cells as visualized by electron microscopy. Some of the recombinant 120 kDa protein expressing E. coli invaded the HeLa cells as determined by gentamicin protection assays and by intravacuolar localization ultrastructurally.