 "T. pallidum"'s outer membrane has the most contact with host cells and contains few transmembrane proteins, limiting antigenicity while its cytoplasmic membrane is covered in lipoproteins.The outer membrane's treponemal ligands main function is attachment to host cells, with functional and antigenic relatedness between ligands.The genus "Treponema" has ribbons of cytoskeletal cytoplasmic filaments that run the length of the cell just underneath the cytoplasmic membrane.