单选题
The belief that the mind plays an important role in physical illness goes back to the earliest days of medicine. From the time of the ancient Greeks to the beginning of the 20th century, it was generally accepted by both physician and patient that the mind can affect the course of illness, and it seemed natural to apply this concept in medical treatments of disease. After the discovery of antibiotics, a new assumption arose that treatment of infectious or inflammatory disease requires only the elimination of the foreign organism or agent that triggers the illness. In the rush to discover antibiotics and drugs that cure specific infections and diseases, the fact that the body's own responses can influence susceptibility to disease and its course was largely ignored by medical researchers. It is ironic that research into infectious and inflammatory disease first led 20th-century medicine to reject the idea that the mind influences physical illness, and now research in the same field — including the work of our laboratories and of our collaborators at the National Institutes of Health — is proving the contrary. New molecular and pharmacological tools have made it possible for us to identify the intricate network that exists between the immune system and the brain, a network that allows the two systems to signal each other continuously and rapidly. Chemicals produced by immune cells signal the brain, and the brain in turn sends chemical signals to restrain the immune system. These same chemical signals also affect behavior and the response to stress. Disruption of this communication network in any way, whether inherited or through drugs, toxic substances or surgery, exacerbates the diseases that these systems guard against: infectious, inflammatory, autoimmune, and associated mood disorders. The clinical significance of these findings is likely to prove profound. They hold the promise of extending the range of therapeutic treatments available for various disorders, as drugs previously known to work primarily for nervous system problems are shown to be effective against immune maladies, and vice versa. They also help to substantiate the popularly held impression(still discounted in some medical circles)that our state of mind can influence how well we resist or recover from infectious or inflammatory diseases. The brain's stress response system is activated in threatening situations. The immune system responds automatically to pathogens and foreign molecules. These two response systems are the body's principal means for maintaining an internal steady state called homeostasis. A substantial proportion of human cellular machinery is dedicated to maintaining it. When homeostasis is disturbed or threatened, a repertoire of molecular, cellular and behavioral responses comes into play. These responses attempt to counteract the disturbing forces in order to reestablish a steady state. They can be specific to the foreign invader or a particular stress, or they can be generalized and nonspecific when the threat to homeostasis exceeds a certain threshold. The adaptive response may themselves turn into stressors capable of producing disease. We are just beginning to understand the interdependence of the brain and the immune system, how they help to regulate and counterregulate each other and how they themselves can malfunction and produce disease.
单选题
The passage supplies information to suggest that______.