alcohol, tumor necrosis factor, and tuberculosis

0145-6008/95/1901-0017$03.00/0 ALCOHOLISM: CLINICAL AND EXPERIMENTAL RESEARCH

Vol. 19, NO. 1 February 1995

Alcohol, Tumor Necrosis Factor, and Tuberculosis Steve Nelson, Carol Mason, Greg Bagby, and Warren Summer

Alcohol exerts potent suppressive effects on the immune system that significanty increase host susceptibility to a variety of infections, particularly pneumonia. Historically, tuberculosis has been strongly associated with alcohol abuse. Although the relationship between alcohol abuse and tuberculosis is widely appreciated, the basic mechanisms by which alcohol immunosuppresses the host remain to be clarified. A major obstacle in furthering our understanding of this association has been the difficulty in distinguishing between the effects of alcohol per se and the other frequent sequelae of alcoholism such as nutritional deficiencies, liver disease, cigarette smoking, hygienic factors, and lifestyle. This article focuses on the role of tumor necrosis factor-alpha (TNF) in host defense and how alcohol modulates the activity of this important cytokine. While TNF’s role in mediating the lethal consequences of infection has been the subject of much conjecture, this review focuses on the emerging evidence that TNF is an essential factor in the normal immune response to numerous infections, including tuberculosis.

Key Words: Tuberculosis, Tumor Necrosis Factor, Cytokine, Pneu- monia, Infection.

T LEAST one-half of the adult population in the A United States consumes alcohol.‘ Among these con- sumers, -15 million abuse or depend on alcohol, making alcoholism the leading form of drug abuse in the United States.’ Because alcohol can exert potent suppressive effects on the immune system, the susceptibility of alcohol users to a wide spectrum of infections is significant and poses an important public health p r~b lem.~” Among these, pulmonary infections have the strongest and best-docu- mented association with alcohol

One of the earliest reports to link alcohol consumption and lung infections was published in 1785 by Benjamin Rush. InAn Inquiry into the Effects ofArdent Spirits upon the Human Body and Mind, Rush listed tuberculosis and pneumonia as infectious sequelae of alcoh~lism.~ Sir William Osler, in his principles and Practice of Medicine, stated that “alcoholism was perhaps the most potent predisposing factor” to pneumonia.8 Indeed, the frequency and severity of pulmonary infections are so pronounced among alcohol abusers that physicians have historically been convinced that the alcohol-consuming patient is, in fact, an immuno- compromised host. However, whereas the relationship between alcohol consumption and pulmonary infection has

From the Departments of PulmonarylCritical Care Medicine and Physi- ology, Louisiana State University Medical Center, New Orleans, Louisiana.

This study was suppofied by the National Institute on Alcohol Abuse and Alcoholism Grants A-07710 and AA-09803.

Reprint requests: Steve Nelson, M.D., PulmonarylCritical Care Medicine, Louisiana State University Medical Center, Suite 3205, MEB, 1901 Perdido Street, New Orleans, LA 70112.

Copyright 0 1995 by The Research Society on Alcoholism.

Alcohol Clin Erp Res, Vol19, No 1, 1995: pp 17-24

been widely appreciated, an understanding of the basic mechanisms by which alcohol suppresses the immune system of the host remains unclear and continues to ev01ve.~ Despite advances in medical technology and antimicrobial development, there has been little decline in the mortality of pneumonia in alcoholic patients. Further progress in reducing disease and death among alcohol abusers who contract these infections will depend on an increased understanding of the means by which alcohol depresses host defenses against invading microorganisms and developing new counteractive treatment strategies.

Pneumonia is the clinical manifestation of infection caused by multiple host and pathogen interactions involv- ing characteristics of the invading pathogen, immunological defenses, nutrition, metabolism, and environmental expo- sures. Because most patients with pneumonia do not have a clinically recognized genetic defect in their host-defense system, their disease is typically the end result of an acquired imbalance resulting from a failure of the immune system to destroy the offending micro~rganism.~

The alveolar macrophage (AM) is positioned as the pri- mary cell in responding to an infectious challenge within the lung.’-’’ It is the only intraalveolar phagocyte and represents the first line of cellular defense for the air spaces of the lower respiratory tract. Traditionally, the macrophage has been viewed primarily as a phagocytic cell. How- ever, macrophages are also active secretory cells and can profoundly influence almost every aspect of the immune and inflammatory responses.12 Prominent among these AM-derived secretory products are the cytokines that me- diate intercellular communication and modulate the host- defense response to infectious challenges. This class of mediators is represented by growth and differentiation, cytolytic, chemotactic, and immunoenhancing factors. Thus, the sequential release of AM-derived cytokines pro- vides a mechanism for the initiation and amplification of the host-defense response to an intrapulmonary challenge and its eventual resolution.

TUMOR NECROSIS FACTOR (TNF) AND INFECTION

TNF-a is one of these proinflammatory mediators derived primarily from mononuclear phagocytes that elicits a myriad of responses in the host.13 When TNF was first identified as a mediator during infection-like states, it was thought to be primarily responsible for many of the dele- terious effects associated with overwhelming infections leading to shock and death. However, the protective effects

17

18 NELSON ET AL.

of TNF and its role in normal immune mechanisms that have led to its preservation throughout mammalian evolu- tion remain to be clarified. Accumulating evidence indi- cates that, in fact, the TNF response is a critical component of the immune response to invading pathogens.

TNF is detectable in the systemic circulation of approxi- mately one-third of critically ill patients and is frequently elevated in proportion to the severity of the underlying infection. Waage et al.14 reported higher serum TNF activity in patients who subsequently succumbed to meningococcal men- ingitis than in those individuals who survived. Since then, other investigators have also found that high circulating levels of TNF seem to correlate with the severity of the underlying illness, but this has not been uniformly observed.”-”

To speculate that higher TNF levels are causally related to the lethal consequences of infections is tempting, but this conclusion cannot be firmly drawn from elevated levels of TNF alone. A number of studies conducted in both patients and animals demonstrate that high TNF levels alone are not sufficient to produce the full complement of adverse symptoms seen during overwhelming infections. For exam- ple, in a study by Kiener et a1.,21 both toxic and nontoxic forms of the lipid-A component of lipopolysaccharide (LPS) produced similar increases in serum TNF. It is therefore likely that multiple factors, such as the duration of the TNF response, the presence of synergistic mediators, and/or endogenous modulators, the site of infection, and the intrinsic susceptibility of the host, are critical determinants of the host’s response to both endogenously released or exogenously administered TNF.

The site of infectious challenge has a substantial impact on the TNF response. Intravenous injections of bacterial endotoxins or live microorganisms yield large transient increases in circulating TNF levels that peak 1-2 hr after challenge, and return to nearly undetectable levels after 3-4 hr.22-24 Under these conditions, we reported that TNF remains nondetectable in fluid lavaged from the lungs of intravenously challenged animals throughout the study period (Table l).23 This observation has just recently been confirmed in humans.25 Likewise, administering LPS or bacteria directly into the lung results in a substantial increase of TNF in bronchoalveolar lavage fluid (BALF), whereas serum levels of TNF remain n~ndetectable .~~ The selective increase in TNF activity, after either intravenous or intrapulmonary infectious challenges, may be essential in compartmentalizing the host’s inflammatory response. Clearly, it would not be advantageous to either nonspecifi- cally or systemically activate the inflammatory cascade dur-

Table 1. TNF Response in Serum and BALF is Dependent on Route of LPS Administration

Peak serum TNF Peak BALF TNF LPS (1.5 hr) (2.5 hr)

None ND

Intravenous High lntratracheal NU

NU

NU

High

ND, nondetectable. Data from Nelson S, et al., J Infect Dis 159:189-194, 1989.

ing a localized infection, because this may inadvertently injure the host. Furthermore, this mechanism may serve to localize the immune response at a specific site or within a selected compartment. In our laboratory, we have shown that a lethal intravenous dose of TNF when administered directly into the lung, is not injurious, but in fact, enhances the antibacterial defenses of the lung.26

Although TNF alone or in combination with other cytokines or bacterial products can produce symptoms similar to those occurring during severe infections, other studies demonstrate that treatment of animals with TNF can po- tentiate the host-defense response to infectious challenges. Nakano and associates27 found that pretreating mice with a single dose of intraperitoneal TNF 6-12 hr before intraperitoneal challenge with Salmonella typhimunum enhanced bactericidal activity against this organism. More- over, the survival rate of infected mice was improved by pretreatment with TNF. Blanchard et al.” were able to protect mice from lethal Legionella pneumophil~a lung infections by locally instilling TNF and demonstrated that such treatments enhanced bacterial clearance of the pathogen from the lungs of infected mice. Havell” and Desiderio et aL3’ were able to protect mice from a lethal dose of Listeria monocytogenes by administering TNF to them 1-24 hr before the bacterial challenge. Pretreatment with TNF has also been shown to afford protection against lethal endotoxemia and peritonitis produced by cecal ligation and puncture.31 Hershman et al.32 found TNF treatment of mice reduced mortality from Klebsiella pneumoniae wound infection when given for 5 days before bacterial challenge, or starting 1 hr after initiating the infection, and continuing therapy for 7 days. Cross et al.33 conducted interesting experiments in C3H/HeJ mice. This murine strain is resistant to endotoxin-induced shock and death, because of the inability of its macrophages to produce TNF in direct response to LPS. However, these investigators found C3H/ HeJ mice to be 100-fold more sensitive to Escherichia coli-induced lethality. Furthermore, pretreatment of C3H/ HeJ mice with a combination of recombinant murine TNF and interleukin (1L)-1 protected mice from this otherwise lethal bacterial challenge.

The consequences of passive immunization with antibodies directed against TNF offer the best means presently available for determining the role TNF plays during infections. Pretreatment of animals with these antibodies protects them from lethal doses of LPS and certain kinds of bacterial and parasitic insults. Beutler et al.34 first demonstrated that passive immunization with anti-TNF serum rendered mice less sensitive to E. coli LPS. Other labora- tories, including our own, have substantiated this find- ing.”2,3s*36 Such data provide compelling evidence that TNF elicited by endotoxin administration participates in its lethal consequences. The detrimental role of TNF has been extended to lethal bacteremia by studies in baboons. Tracey et al.24 found that neutralizing monoclonal anti-TNF antibodies prevented death from a lethal intravenous challenge

TNF AND HOST DEFENSE 19

of live E. coli if administered 2 hr before the bacterial challenge. An anti-TNF antibody used by Hinshaw et al.37 was also effective when administered to baboons 30 min after initiating a 2-hr infusion of bacteria.

However, lethality after other types of infections is not uniformly prevented by using antibodies against TNF. A lack of efficacy with anti-TNF antibodies has been reported in animals subjected to bacterial peritonitis. Evans et al.35 were unable to prevent mortality from cecal ligation and puncture by pretreating mice with a monoclonal antibody directed against murine TNF. We have also attempted to reduce the mortality induced by bacterial peritonitis in an E. coli fecal inoculum model, without success.36 In contrast, the antibody did significantly improve survival in animals that were challenged with intravenous LPS or E. coli. Thus, significant differences exist between intravascular models of infection and localized infections, such as bacterial peritonitis. Whereas TNF plays an important role in the lethal consequences of vascular models of infection, its role during severe focal infections remains to be established. These studies underscore the fact that anti-TNF therapy is not uniformly efficacious in mitigating the adverse consequences of severe infections. Which model system more closely parallels the clinical scenario remains to be determined, but it is interesting to note that human trials of anti-TNF to date have not shown efficacy in septic patients?*

ALCOHOL AND TNF

If TNF plays an important role in the inflammatory cascade supporting host defense, then factors modulating its production and release become critically important in understanding the pathophysiological events leading to infection. Infection, particularly pneumonia, contributes sub- stantially to the morbidity and mortality among individuals abusing alcohol, suggesting that alcohol is a potent immunosuppressive factor that undermines the normal host-immune response. To investigate the effects of acute and chronic alcoholism on TNF activity, we initially examined the response of rats challenged with either intravenous or intratracheal LPS.39 Four groups of animals were studied: normal, acute alcohol intoxication, chronic alcoholic, and acute intoxication of chronic alcoholic rats. TNF activity in serum and BALF was determined over time. Total and differential cell counts in BALF and serum were quanti- tated, and histopathology of the lung examined.

As observed in previous studies, intravenous LPS produced large increases in serum TNF in normal animals. The response was transient, with peak levels occurring 90 min after LPS injection. By the third post-LPS hour, TNF levels had nearly returned to baseline levels. A similar time course was observed in chronic alcoholic rats, in which peak serum TNF levels did not differ from the levels seen in LPS-injected nonalcoholic rats. In contrast to these two groups, the LPS-induced increase in serum TNF levels was virtually abolished in nonalcoholic and chronic alcoholic

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Fig. 1. Effect of acute alcohol administration on LPS-induced TNF in serum (0) and lung (B) in chronic alcohol-fed rats.

rats given an acute injection of ethanol (Fig. 1). In these animals, blood ethanol levels were in the range of 300 mddl during the 4-hr observation period. In subsequent studies, we showed that ethanol suppressed LPS-induced TNF in a dose-dependent fashion.40

A similar response was observed in rats challenged in- tratracheally with LPS. Nonalcoholic and chronic alcohol rats given an intratracheal challenge with LPS had substantial levels of TNF in fluid lavaged from their lungs at 1 and 4 hr. In contrast, BALF TNF levels were markedly suppressed in both groups when they received an acute dose of alcohol before the LPS challenge (Fig. 1).

A different pattern emerged when TNF levels were as- sessed in A M s lavaged from the lungs of the four treatment groups. Whereas TNF is barely detectable in association with AMs obtained from rats not treated with LPS, cell- associated TNF was significantly increased after intratracheal LPS challenge. Unlike the attenuation observed in LPS-induced increases in BALF TNF with acute alcohol administration, the response of cell-associated TNF to in- stilled LPS was not dampened by acute alcohol intoxication. However, rats on the alcohol-containing diet did have significantly lower levels of cell-associated TNF. Recently, both membrane and cytoplasmic TNF have been demonstrated by immunohistochemical techniques in activated macro phage^.^^ It is known that alcohol markedly affects membrane fluidity and disrupts membrane str~cture.~’ Ad- ditionally, recent studies indicate that chronic alcohol consumption decreases the number of TNF cell-surface receptors on AMs (Drs. I. Deaciuc and N. D’Souza, personal communication). Perhaps these and other changes alter the distribution between cell-associated and secreted TNF from cells following appropriate stimulation. This would explain, in part, why some observers have reported increased levels of TNF following LPS challenge in rats on a chronic alcoholic diet.43

If TNF is an important factor in normal host defenses, then an impaired TNF response should be associated with an increased susceptibility to infections. These in vivo experiments demonstrate that acute alcohol intoxication markedly inhibits both the systemic and intrapulmonary

20 NELSON ET AL.

TNF response to E. coli LPS. Within the lung, this suppression of LPS-induced TNF was associated with a markedly impaired inflammatory response. Acute ethanol administration significantly suppressed (>90%) the number of polymorphonuclear leukocytes (PMNs) recruited into the bronchoalveolar space in response to intratracheal LPS. The additional phagocytic capacity afforded by the normal influx of PMNs into the lung in response to bacteria is known to contribute essential defense capabilities to lung host defense.” In subsequent studies, we showed that acute alcohol intoxication similarly suppresses lung TNF elicited in response to intrapulmonary challenges with Staphylococ- cus aureus and K p n e ~ m o n i a e . ~ ~ In these studies, the suppressed TNF response was associated with proliferation of the bacteria within the lung. To determine if alcohol-induced inhibition of TNF is an important mechanism con- tributing to the immunosuppressive effects of alcohol, we next studied the effect of an anti-TNF antibody on the antibacterial defenses of the lung in animals challenged with a gram-negative pathogen.45 These studies showed that treatment of rats with anti-TNF IgG before an aerosol inhalational challenge with Pseudomonas aeruginosa-suppressed PMN recruitment into the alveolar compartment by -8-fold and significantly suppressed intrapulmonary bactericidal activity. Thus, alcohol-induced suppression of TNF is a mechanism underlying ethanol’s reported delete- rious effects on PMN delivery to a site of infection and host defenses.

Recently, McClain and C ~ h e n ~ ~ reported that incubation of monocytes isolated from healthy individuals with ethanol suppressed LPS-stimulated TNF in vitro. Interestingly, monocytes from patients with alcoholic hepatitis had significantly increased spontaneous and LPS-stimulated TNF release compared with monocytes from healthy volunteers. These findings suggest the occurrence of in vivo activation of these cells in patients with alcoholic hepatitis. In contrast, monocytes from patients with cirrhosis have a depressed LPS-induced TNF response.47 These apparently discrepant findings may result from the degree of underlying endotoxemia in these patient groups. It is known that the majority of patients with cirrhosis have detectable endotoxemia that likely results from translocation of LPS from the gastrointestinal tract combined with diminished hepatic clearance.48 We have recently shown in an animal model that repeated doses of intravenous LPS leads to a failure of the animals to generate a subsequent systemic TNF resp0nse.4~ Perhaps these findings of altered TNF responses in patients relate to the development of oral tolerance, which follows the progressive loss of intestinal barrier function, resulting in a state of acquired immune deficiency.

ALCOHOL, TUBERCULOSIS, AND TNF

Tuberculosis is an infection caused by the organism My- cobactenum tuberculosi~.~~ It is acquired by inhaling infectious droplet nuclei that enter the lower respiratory tract.

Interestingly, of those individuals infected with M. tuberculosis, only 10% will develop clinically apparent disease. The United States is presently experiencing a resurgence of tuberculosis that has been linked to the acquired immunodeficiency syndrome (AIDS) pandemic and the emergence of antimicrobial-resistant tubercle bacilli. Since 1985, case rates of tuberculosis in this country have risen, ending three decades of decline.” From 1984 through 1991, -39,000 excess cases have been reported.52 This increase in the prevalence of tuberculosis is alarming for several reasons. First, it is one of the first infections associated with human immunodeficiency virus (HIV) infection that can be trans- mitted to normal hosts in the absence of direct contact and in spite of appropriate precautions, thus conveying a substantial risk for infection to the general population. Second, recently described strains of tuberculosis are resistant to multiple standard antituberculous regimens. When the organism is resistant to two or more of these agents, the case fatality rate of this disease approximates These strains pose an ominous threat to the health of patients, as well as those with whom they come into close contact, including health care providers. It is estimated that the financial impact of these excess cases of tuberculosis occurring since 1985 exceeds $600 million.53

The medical literature is replete with publications show- ing an association between alcoholism and tuberculous infections. Studies from the United States, Canada, Great Britain, Denmark, Yugoslavia, and Australia have demonstrated a significantly greater incidence of newly identified cases of pulmonary tuberculosis among alcoholics than in nonalcoholics or in the general p ~ p u l a t i o n . ~ ~ ” ~ However, a major problem in furthering our understanding of this association has been the difficulty in distinguishing between the effects of alcohol per se and the other frequent sequelae of alcoholism, such as nutritional deficiencies, alcoholic cirrhosis, cigarette smoking, hygienic factors, and lifestyle.

Jones et al.57 found a rate of active new cases of tuberculosis in homeless men with an alcoholism rate of 70% in a Minneapolis rehabilitation center of 22.2 cases/1000. This rate was 55.5 times the rate of tuberculosis among the general population, which was 0.4/1000 for the same time period of the survey. In a chest x-ray screening study of prisoners in Toronto, Olin and Grzyb~wsk i~~ found chest radiographic findings consistent with active or past tuberculosis in 16.8% of chronic alcoholics compared with a rate of 1.1% in other prisoners. The rate of positive tuberculin skin tests was 80.6% in the chronic alcoholics compared with 33.3% in the other inmates, At Grady Memorial Hos- pital in Atlanta, GA, Feingold6’ reported that 54% of patients diagnosed with tuberculosis in the outpatient clinic were alcoholic, compared with 5% in a random sample of the general clinic’s population. Similarly, patients diagnosed with tuberculosis in the emergency room of the hospital had a 69% rate of alcoholism, compared with an 18% rate in a general patient sample. A survey of patients with tuberculosis in Australia showed that the level of

21 TNF AND HOST DEFENSE

alcohol consumption was correlated with the risk of acquir- ing this infection.61 Light drinkers had only a slightly higher risk of tuberculosis than nondrinkers, whereas heavy drinkers were most prone to infection. Most recently, Carpenter and Huang62 reported the incidence of tuberculous pulmonary infections admitted to Parkland Memorial Hospital in Dallas, TX, a public municipal hospital. In this study, tuberculosis was again much more common in alcoholics than in nonalcoholics. Overall, 39% of all pulmonary infections in alcoholics were due to tuberculosis. Interestingly, the clinical and radiographic features of alcoholics with tuberculosis did not differ from those seen in nonalcoholics. Furthermore, the number of cases of tuberculosis in the present study was strikingly similar to those previously reported in the literature over 30 years ago.

As previously mentioned, it is debatable whether or not this increased incidence of tuberculosis is due to the mul- tifactorial immunological deficiency in alcoholics or to a lifestyle that permits increased exposure to other patients with tuberculosis. The greater susceptibility among alcoholics to tuberculosis has been attributed to crowded, dormi- tory-style living conditions. Such an environment would significantly increase the chances of an individual becoming infected and subsequently spreading the infection to others. Studies have been done that have analyzed factors in addition to alcohol that may have been directly or indirectly related to the development of tuberculosis in the alcoholic patient. Lewis and Chamberlai# were unable to show that any of the indirect factors examined, such as occupation, marital status, smoking habits, or race, were responsible for the increased rate of tuberculosis in the alcoholics studied. In a separate study, the role of smoking and drinking habits were examined in a series of patients with pulmonary tuberculosis, and alcohol, not tobacco, seemed to be inde- pendently linked with tubercul~sis .~~

In addition to being associated with a greater frequency of tuberculosis, alcohol abuse poses significant problems in effective therapy. These patients are difficult to convince that they should seek medical attention and hospitalization, they have greater difficulty adhering to hospital routines and rules, and they more frequently leave the hospital against medical advice. Once discharged from hospital, they are less compliant in taking their medications, more likely to miss scheduled outpatient clinic visits, and are more frequently lost to follow-up. All of these problems result in high relapse rates and the development of resistant organisms that are exceedingly more difficult to eradicate. In a study by Milne,6l he found that alcoholic patients had more extensive pulmonary disease, took longer to treat, had greater noncompliance in taking their medications, and had more complications from their chemotherapy. Kok- Jensed3 reported that only 36% of alcoholic patients com- pleted their recommended therapy, compared with 78% of the nonalcoholics. Consistent with the greater extent of disease when they first present with tuberculosis, alcoholics also have a higher risk of death during the initial hospitalization.@

The host-defense mechanisms underlying the increased susceptibility of alcoholics to tuberculosis remain unclear. Both in vitro and in vivo studies have shown that alcohol impairs various aspects of cell-mediated immune func- t i o n ~ ? , ~ ~ Immune defense mechanisms against M. tuberculosis involve cell-mediated immunity that is normally re- quired to mount a host granulomatous response to contain or eliminate these pathogen^.^',^^,^^ For the great majority of infected individuals, this immune response will contain the infection and prevent clinical manifestations of disease. The infection may, however, become reactivated later in life and cause disease. Various immunosuppressive agents, such as corticosteroids, cytotoxic drugs, and radiotherapy can increase the likelihood of a reactivation of tuberculosis. Certain illnesses such as cancer, HIV infection, renal failure, and nutritional deficiency also increase the likelihood of reactivation. To date, alcohol alone has not been specif- ically shown to induce reactivation of tuberculosis.

Cell-mediated immunity normally develops over several weeks, so that earlier host-defense mechanisms are also likely to play a critical role in the resistance of the host to mycobacteria. These early responses following exposure of the lower respiratory tract to mycobacterial pathogens probably occur on several fronts, including the interaction of the organism with alveolar lining fluid or surfactant component^,^^-^' the initial interaction of the pathogen with the AM,71-73 and the production of reactive oxygen74 and nitrogen intermediate^.^'-^^ AMs ingest and destroy (or inhibit) >90% of inhaled tubercle bacilli?' The tubercle bacilli not destroyed by the AM multiply intracellularly and are subsequently released when these macrophages die. Thus, the initial interaction of this pathogen with the AM plays a critical role in the eventual containment or development of this disease.

The mechanisms by which this intracellular pathogen evades the microbicidal effector functions of the AM are poorly understood. It is known that mycobacteria synthe- size and secrete large amounts of lipoarabinomannan (LAM).79 LAM is broadly related to LPS of Gram-negative bacteria. LAM contains two fatty acyl residues as part of the phospholipid end, a mannan core, and an antigenic arabinan end, and is clearly analogous to lipid A, the inner and outer core, and the 0-Ag regions of LPS. LAM exhibits immunoregulatory effects that favor mycobacterial survival, including suppression of T-cell proliferation," inhibition of macrophage activation,81'82 and neutralization of toxic oxygen-free radicals.83 It is known that LAM, like LPS, is also an inducer of macrophage-derived cytokines, including TNF, IL-1, IL-6, IL-8, IL-10, and granulocyte macrophage- colony-stimulating factor.79 Most interestingly, the capacity of LAMS from different mycobacteria to elicit TNF secretion from mononuclear cells seems to relate to the virulence of the strain. Chatterjee et aLg4 have recently reported that LAM from the avirulent H37Ra strain of M. tuberculosis is 100-fold more potent at inducing TNF secretion than LAM from the virulent Erdman strain. TNF is

22 NELSON ET AL.

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reported to have direct antimycobacterial properties and inhibits mycobacterial growth in ~ i t r o . ~ ~ TNF has been found to have a beneficial effect on survival when infused after pathogen inoculation in a murine model of M. tuber- cuZosis.86 Animal studies further suggest that TNF may inhibit the extent of mycobacterial infection by mediating granuloma formation in V ~ V O . ~ ~ Elevated concentrations of TNF have been found in the pleural fluid of patients with tuberculous pleuritis,” and cells secreting TNF have been demonstrated at the site of tuberculin-induced skin reac- tions in humans,” suggesting a role for TNF in the human immune response against mycobacteria. Therefore, the capacity for a given mycobacterial isolate to cause disease may directly relate to its ability to either elicit or avoid TNF-mediated mechanisms of resistance. Thus, the lesser potency of the LAM from the virulent Erdman strain to elicit a “sufficient” TNF response may be central to the ability of this particular organism to proliferate in an un- restrained fashion within infected host AMs before the generation of cell-mediated immunity.

Mendenhall et al.90 reported that chronic alcohol inges- tion in rats infected with bacillus Calmette-GuCrin (BCG) was associated with a 10-fold increase in colony-forming units compared with pair-fed controls. Interestingly, administration of an anti-TNF antibody in a similar model of BCG infection 1-2 weeks after BCG challenge interfered with the development of granulomas and subsequent elimination of these microorganism^.^^ Thus, the observed susceptibility of alcohol-consuming patients to tuberculosis may be, in part, related to alcohol-induced inhibition of TNF. Furthermore, .alcohol has been shown to abrogate TNF-induced mycobactericidal activity in isolated macrophages.’’ It is known that alcohol downregulates the expression of macrophage TNF receptors9’ and may affect cellular mechanisms of signal transduction:’ which would lead to varying degrees of cellular unresponsiveness to stirnulatory signals.

If the TNF response of the host following exposure to mycobacteria is important in the resistance of that host to infection, then it may be possible to augment immune defense mechanisms via the exogenous administration of cytokines. We have reported that interferon-? can attenu- ate alcohol-induced inhibition of TNF in vivo in both serum and lung (Fig. 2).93 We have also recently found that IFN can enhance the TNF response of Ah4s following intratracheal challenge with LAM in vivo (Fig. 3). Jaffe et al.94 have shown that recombinant interferon can be safely targeted to the lung in humans resulting in Ah4 activation. These findings suggest that such an approach may be of benefit in augment- ing host defenses in susceptible hosts with M. tuberculosis. Furthermore, such therapy may discourage the emergence of antibiotic-resistant strains of M. tuberculosis.

CONCLUSION

In summary, emerging data indicate that the alcohol- abusing patient is seriously undermined by profound dis-

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turbances in cytokine production and activity. These alter- ations may play a critical role in the development of their immunosuppressed status. Although a great deal of attention has been given to TNF‘s role in the lethal consequences of infection, we believe that the evidence suggesting a positive role for TNF in the host’s fight against invading pathogens, such as M. tuberculosis, is equally compelling and deserves further investigation. Hopefully, such information will provide the foundation for the development of strategies to reconstitute immunologically and re- store immune defenses in these compromised hosts that may prevent the development and mitigate the severity of their infectious complications.

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TNF AND HOST DEFENSE 23

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16. Calandra T, Baumgartner JD, Grau GE, Wu MM, Lambert PH, Schellekens J, Verhoef J, Glauser MP: Prognostic values of tumor necrosis factor/cachectin, interleukin- 1, interferon-alpha, and interferon-gamma in the serum of patients with septic shock. J Infect Dis 161:982-987, 1990

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21. Kiener PA, Marek F, Rodgers G, Lin PF, Warr G, Desiderio J: Induction of tumor necrosis factor, IFN-gamma, and acute lethality in mice by toxic and non-toxic forms of lipid A. J Immunol 141:870-874, 1988

22. Mathison JC, Wolfson E, Ulevitch RJ: Participation of tumor necrosis factor in the mediation of gram negative bacterial lipopolysaccharide-induced injury in rabbits. J Clin Invest 81:1925-1937, 1988

23. Nelson S, Bagby GJ, Bainton BG, Wilson LA, Thompson JJ, Sum- mer WR: Compartmentalization of intraalveolar and systemic lipopolysaccharide-induced tumor necrosis factor and the pulmonary inflammatory response. J Infect Dis 159:189-194, 1989

24. Tracey KJ, Fong Y, Hesse DG, Manogue KR, Lee AT, Kuo GC, Lowly SF, Cerami A Anti-cachectinA’NF monoclonal antibodies prevent septic shock during lethal bacteraemia. Nature 330:662-664, 1987

25. Boujoukos AJ, Martich GD, Supinski E, Suffredini AF: Compart- mentalization of the acute cytokine response in humans after intravenous endotoxin administration. J Appl Physiol 74:3027-3033, 1993

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End of Symposium

alcohol, tumor necrosis factor, and tuberculosis

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