Alcohol and the immune system.

Abstract

are program directors in the Division of Metabolism and Health Effects, National Institute on Alcohol Abuse and Alcoholism, Rockville, Maryland. Clinicians have long observed an association between excessive alcohol consumption and adverse immune-related health effects such as susceptibility to pneumonia. In recent decades, this association has been expanded to a greater likelihood of acute respiratory stress syndromes (ARDS), sepsis, alcoholic liver disease (ALD), and certain cancers; a higher incidence of postoperative complications; and slower and less complete recovery from infection and physical trauma, including poor wound healing. This issue of Alcohol Research: Current Reviews (ARCR) summarizes the evidence that alcohol disrupts immune pathways in complex and seemingly paradoxical ways. These disruptions can impair the body's ability to defend against infection, contribute to organ damage associated with alcohol consumption, and impede recovery from tissue injury. It is our hope that a greater understanding of the specific mechanisms through which alcohol exerts its effects on the immune system may lead to development of interventions to prevent, or at least mitigate, the negative health consequences of alcohol misuse. Contributors to this issue of ARCR lay the groundwork for understanding the multilayered interactions between alcohol and immune function by presenting an overview of the immune system (see the article by Spiering) and by reviewing current research on the effects of alcohol on innate immunity (see the article by Nagy) and on adaptive immunity (see the article by Pasala and colleagues). As reviewed by Szabo and Saha, alcohol's combined effects on both innate and adaptive immunity significantly weaken host defenses, predisposing chronic drinkers to a wide range of health problems, including infections and systemic inflammation. Alcohol's widespread effects on immune function also are underscored in the article by Gauthier, which examines how in utero alcohol exposure interferes with the developing immune system in the fetus. This exposure increases a new-born's risk of infection and disease; additional evidence suggests that alcohol's deleterious effects on immune development last into adulthood. The gastrointestinal (GI) system is typically the first point of contact for alcohol as it passes through the body and is where alcohol is absorbed into the bloodstream. One of the most significant immediate effects of alcohol is that it affects the structure and integrity of the GI tract. For example, alcohol alters the numbers and relative abundances of microbes in the gut microbiome (see the article by Engen and colleagues), an extensive community of microorganisms in the intestine that aid in normal gut function. These organisms affect the maturation and function of the immune system. Alcohol disrupts communication between these organisms and the intestinal immune system. Alcohol consumption also damages epithelial cells, T cells, and neutrophils in the GI system, disrupting gut barrier function and facilitating leakage of microbes into the circulation (see the article by Hammer and colleagues). These disruptions to the composition of the gut microbiota and to gut barrier function have important implications beyond the intestinal system.