Answer: As a survival mechanism, stress causes the sympathetic nervous system to release hormones. The hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) axis both generate these chemicals.
Explanation: What is immune system?
A network of biological processes called the immune system guards an organism against disease. It recognizes and reacts to a wide range of pathogens, separating them from the organism's own healthy tissue, including viruses, parasitic worms, cancer cells, and things like wood splinters. There are two main immune system subsystems seen in many species. The innate immune system responds to a variety of events and stimuli in a predetermined way. The adaptive immune system learns to recognize chemicals it has previously met and responds to each stimulus in a way that is specific to that stimulus. Both rely on molecules and cells to carry out their respective tasks.
Almost all living things have some sort of immune system. Bacteria have a simple immune system in the form of defense-inducing enzymes.