Interestingly, these two immune pathways interact and antagonize one another. It's not completely clear if this is a form of adaptive regulation or an evolutionary constraint. However, when salicylic acid is induced, levels of jasmonic acid go down. Conversely, when jasmonic acid is induced, salicylic acid goes down. It may seem strange to have different immune response react adversely to each other, but in animals we see similar cross-talk happen in the immune system. Different arms of the mammalian immune system down-regulate each other as a means of regulation that keeps immune responses from spiraling out of control. A similar regulatory role between the different parts of plant immune responses may explain the the antagonism between Salicylic acid and Jasmonic acid.