CCL2 and syphilis: At the moment the function of Tp15 is still unknown, while Tp17 is characterized as an eight-stranded β-barrel protein with a shallow “basin” at one end of the barrel and an α-helix stacked on the opposite end [23], which probably plays a role in either protein ligand binding, treponemal membrane architecture maintenance [24], or syphilis pathogenesis by activation of the expression of intercellular adhesion molecule 1 (ICAM-1), E-selectin, and monocyte chemoattractant protein-1 (MCP-1) genes in endothelial cells [25].