Chronic psychological stress impairs health and induces various diseases by causing an imbalance in the immune, neuropsychiatric and endocrine systems. The primary reason for the development of stress-induced disease is suppression of macrophage function, which plays a pivotal role in innate immunity. In fact, surgical stress has been shown to exacerbate opportunistic infections by significantly suppressing macrophage function. Conversely, administration of macrophage activating substances before surgery, such as tumor necrosis factor (TNF)-α or Picibanil (OK-432), has been shown to protect against macrophage suppression and the resulting exacerbation of infectious diseases, and against tumor metastasis in the lungs. Thus, if suppression of macrophage function by stress could be safely prevented by use of a macrophage activating substance, the detrimental side effects of stress could be reduced. Recently, we identified a lipopolysaccharide, IP-PA1, derived from Pantoea agglomerans, a symbiotic Gram-negative bacteria found in wheat and other food plants. Oral administration of IP-PA1 demonstrated macrophage activation (priming) and protective effects against infection, allergy and cancer, without any side-effects. In this review, the possibility of using IP-PA1 as a safe, macrophage activating substance for prevention of stress-induced impairments is discussed.