Migration of Treponema pallidum through a keratinocyte layer.
Treponema pallidum is the causative agent of the sexually transmitted disease, syphilis. The organism can not be cultured in vitro, which has inhibited the understanding of the pathogenesis of syphilis. There has been no evidence of a treponemal toxin but adherence of large numbers of treponemes is able to destroy cell monolayers of different cell types (Fitzgerald et al, 1982). Non-pathogenic treponemes failed to adhere to cultured cells and this suggests that adherence is associated with virulence of T. pallidum (Fitzgerald et al, 1977). In this study we explored the interaction of T. pallidum with HaCaT cells which are immortalized human keratinocytes with characteristics equivalent to their natural counterpart. The adhesion assay confirmed binding of the organism to HaCaT cell monolayers. Migration assays and electron microscopy revealed that T. pallidum migrates through a confluent keratinocyte layer and western blotting experiments that differentiate between soluble and insoluble occludin confirmed that T. pallidum does not loosen the tight junctions. It is concluded that T. pallidum passes through the keratinocyte layer by trans-cellular rather than inter-cellular migration.