According to studies in psychoneuroimmunology, how does long-term stress affect immunity?

The effects of stress on the body can and is very extreme, especially on the immune system. Being in a stressful situation causes chemicals that are stress hormones to to be supplied to the body which is useful but too much can interfere with the functions of the immune system. This can cause a greater risk of tissue damage and infection but not only that it reduces the amount of white blood cells.