In shrimp, proPO was found to be required for defense against microbial pathogens. In Pacific white shrimp, Litopenaeus vannamei, proPO was shown to be involved in acutephase immune defense against Vibrio alginolyticus and was also found to be regulated by ecdysone, a hormone that promotes growth and controls molting, which suggests that it may participate in other physiological processes. Meanwhile, the expression of two different forms of proPO in L. vannamei was found to be inhibited by WSSV infection