Alcohol and the immune system

Alcohol Health & Research World, Wntr, 1992 by Gary A. Roselle

Research demonstrating alcohol's adverse effects on functions of the immune system supports clinical evidence of an increased incidence of infections among alcoholics.

Scientist have long debated the effects of alcohol on immune function. Laboratory evidence indicates that alcohol can directly suppress various immune responses, and clinical studies have found alcohol abuse to be associated with an increased incidence in a number of infectious diseases. Still, the linkage between alcohol consumption, altered host immune responses, and infection remains controversial and incompletely understood.

Clinical evidence supports a correlation between excessive alcohol consumption and certain bacterial infections. For example, alcoholics who have developed cirrhosis of the liver are predisposed to spontaneous bacterial peritonitis. Phagocytes are an important defense against infection in this part of the body--and defects in phagocytic cell function, observed in many alcoholics, may predispose these individual to peritoneal infection. In addition, infections caused by intracellular bacteria such as Mycobacterium tuberculosis (tuberculosis) and Listeria monocytogenes (meningitis) often are seen in patients who abuse alcohol (see the article by Jacobson, pp. 39-45). These infections may result in part from defects in B- and T-cell functions caused by excess alcohol use. Alcoholics are susceptible to pneumonia caused by a variety of aerobic (oxygen-dependent) and anaerobic (oxygen-independent) microorganisms. Chronic alcohol abuse may cause abnormalities in the functions of alveolar phagocytes, and may decrease the quantity of lung surfactant(1), changes that may interfere with clearance of bacteria from the lungs (see the article by Nelson et al., pp. 73-80).

But it is important to realize that other factors, unrelated or indirectly related to immune function, contribute to alcohol-associated predisposition for infection (see Table 1). For example, intoxication to the point of reduced consciousness may lead to inadvertent aspiration into the lung of bacteria found in the upper respiratory airways, increasing the risk for contracting pneumonia. Among the many alcoholics whose socioeconomic status is poor, overcrowded living conditions and limited access to health care may increase the likelihood of contracting and spreading disease. In addition, many alcoholics suffer from malnutrition and liver disease, conditions that may themselves compromise the immune system's capacity to resist infection (see the articles by Mendenhall, pp. 23-28, and Rosman, pp. 48-56).

The complex nature of the problem has led researchers to develop and utilize in vitro systems and animal models--in laboratory experiments that allow better control for environmental, nutritional, and other factors associated with alcoholism in humans. Research advances describing the cells and mechanisms that confer resistance from disease have facilitated efforts to understood alcohol's effects on the immune system. Improved laboratory techniques to investigate functions of the immune system have helped to delineate immunologic abnormalities in persons who abuse alcohol and in animal models of alcohol use. The main focus of this article is on research describing alcohol's influence on various components and functions of the immune response.

EFFECTS ON LYMPHOID ORGANS AND LYMPHOCYTE DISTRIBUTION

Early studies of alcohol's influence on immune responses examined whether alcohol alters the numbers or ratios of lymphocytes and lymphocyte subpopulations found in the blood. These studies consistently showed a decrease in the numbers of lymphocytes isolated from the blood of alcoholic humans or from laboratory animals that had consumed alcohol over a period of several weeks. These lymphocytes also responded abnormally to in vitro stimulation by mitogens or antigens, suggesting an adverse effect on their capacity to react appropriately to infection (Grossman et al. 1988; Roselle et al. 1990).

Improved technology for characterizing and isolating different types of lymphocytes (B-cells, T-cells, and various T-cell subpopulations) have allowed investigators to determine alcohol's effects on the numbers and functions of lymphocyte populations. One group of researchers has found numbers of circulating helper T-cells and cytotoxic or suppressor T-cells to be reduced in alcoholics (Roselle et al. 1988). The same study observed that T-cell deficits were temporary and at least partially reversible following abstinence from alcohol (Roselle et al. 1988). Alterations in circulating lymphocyte numbers could contribute to increased susceptibility to infection.

In contrast, other investigators have found no abnormalities in the numbers of lymphocytes within particular subpopulations or in relative proportions (ratios) of various T-cell subpopulations isolated from the blood of alcoholics (Jovanovic et al. 1986; Ishimaru and Matsuda 1990). Differences between these reports and those of Roselle and co-workers remain to be explained.