The exact mechanism by how the V-antigen exerts it virulence is not completely known. There are reports showing that Vantigen is secreted into the growth medium and the secretion is important for virulence [24, 25] . The secretion of V-antigen in the medium has been described to be dependent on contact with the host cell, and could also be directed into the host cell by a Yersinia outer proteins (Yops) dependent secretion (Ysc) type III system (TTSS) [26] [27] [28] . It also has been suggested that free V-antigen may enter the cell by endocytosis besides being injected into the cell by the Ysc TTSS [29] . Once inside the host-cell, we do not know exactly what host proteins interact with the intracellular Vantigen [29] . Nevertheless, there is some evidence that anti-V antibodies enhance phagocytosis through possibly the Fc receptor, and thereby block Yop delivery into the host cell, and thus preventing Ysc dependent TTSS injection of V-antigen into the host cell [30, 31] .