**6. Conclusion**

Superoxide's are the critical molecules produced by host cells to counter intracellular pathogens during infection. ROS is mainly produced within mitochondria of cells as byproducts of normal cell respiration. Defects in oxidative phosphorylation in cells could lead to an increase or decrease in ROS production by host cells. ROS-mediated destruction can directly affect the components of the electron transport system of host cells. Therefore, to reduce the ROS activity, host cells are evolved with three types of SODs such as NiSOD, Fe or MnSOD, and CuZnSOD to control the ROS activity produced by itself. More importantly, the immune cells of the host used ROS as defense molecules against various kinds of human pathogens during their infection.

Intracellular pathogens are also furnished with all types of SODs such as NiSOD, Fe or MnSOD, and CuZnSOD. Pathogens are using these SODs in neutralizing the free radicals produced by host cells during infection. SODs of intracellular pathogens can modulate the interaction with phagocytic cells at the onset of phagocytosis by altering the local concentrations of superoxide anion in parasitophorous vacuoles of host cells. SODs of these pathogens are also required to neutralized O2- generated by IFN-γactivated macrophages, but not necessary for survival in quiescent macrophages. However, the role of SOD in combating other infection does not solely depend on the phagocytic ability of macrophages. In conclusion, SODs of intracellular pathogens are the key determinants of their survival inside the host niche. Furthermore, it also plays a vital role in the severity of disease and virulence of these pathogens by protecting them from extracellular host-derived ROS activity.
