of Y. pestis to evade immune system cells. In macrophages, YopH has been shown to dephosphorylate p130Cas, Fyb (FYN binding protein) SKAP-HOM and Pyk, a tyrosine kinase homologous to FAK. YopH also binds the p85 subunit of phosphoinositide 3-kinase, the Gab1, the Gab2 adapter proteins, and the Vav guanine nucleotide exchange factor. YopE functions as a GTPase-activating protein for members of the Rho family of GTPases such as RAC1. YopT is a cysteine protease that inhibits RhoA by removing the isoprenyl group, which is important for localizing the protein to the cell membrane. YopE and YopT has been proposed to function to limit YopB/D-induced cytolysis. This might limit the function of YopB/D to create the pores used for Yop insertion into host cells and prevent YopB/D-induced rupture of host cells and release of cell contents that would attract and stimulate immune system responses. YopJ is an acetyltransferase that binds to a conserved α-helix of MAPK kinases. YopJ acetylates MAPK kinases at serines and threonines that are normally phosphorylated during activation of the MAP kinase cascade. YopJ is activated in eukaryotic cells by interaction with target cell phytic acid (IP6). This disruption of host cell protein kinase activity causes apoptosis of macrophages, and this is proposed to be important for the establishment of infection and for evasion of the host immune response. YopO is a protein kinase also known as Yersinia protein kinase A (YpkA). YopO is a potent inducer of human macrophage apoptosis. It has also been suggested that a bacteriophage – Ypφ – may have been responsible for increasing the virulence of this organism. Depending on which form of the plague infects the individual, the plague develops a different illness; however, the plague overall affects the host cell's ability to communicate with the immune system, hindering the body bringing phagocytic cells to the area of infection. Y. pestis is a versatile killer. In addition to rodents and humans, it is known to have killed camels, chickens, and pigs. Domestic dogs and cats are susceptible to plague, as well, but cats are more likely to develop illness when infected. In either, the symptoms are similar to those experienced by humans, and can be deadly to the animal. People can be exposed by coming into contact with an infected animal (dead or alive), or inhaling infectious droplets that a sick dog or cat has coughed into the air. Immunity A formalin-inactivated