Cocaine facilitation of cryptosporidiosis by murine AIDS in male and female C57/BL/6 mice

Shooting up: the interface of microbial infections and drug abuse

Illicit drug control has been on the global agenda for more than a century. Infections have long been recognized as one of the most serious complications of drug abuse. Drug users are susceptible to pulmonary, endovascular, skin and soft tissue, bone and joint, and sexually transmitted infections caused by a wide range of bacterial, viral, fungal and protozoal pathogens. In addition, injection drug users are at increased risk for parenterally acquired infections such as human immunodeficiency virus, hepatitis B virus, hepatitis C virus, tetanus and malaria. Factors related to drug use, such as unsterile injection practices, contaminated drug paraphernalia and drug adulterants, increase the exposure to microbial pathogens. Illicit drugs also affect several components of the complex immune system and thus modulate host immunity. In addition, lifestyle practices such as multiple sexual partners, overcrowded housing arrangements and malnutrition serve as co-factors in increasing the risk of infection. In this review we present an overview of the unique aspects of microbial pathogenesis, immune modulation and common infections associated with drug use. We have restricted the definition of drug abuse to the use of illegal drugs (such as opiates, marijuana, cocaine, heroin and amphetamines), not including alcohol and nicotine.

Microbial infections, immunomodulation, and drugs of abuse

The use of recreational drugs of abuse has generated serious health concerns. There is a long-recognized relationship between addictive drugs and increased levels of infections. Studies of the mechanisms of actions of these drugs became more urgent with the advent of AIDS and its correlation with abused substances. The nature and mechanisms of immunomodulation by marijuana, opiates, cocaine, nicotine, and alcohol are described in this review. Recent studies of the effects of opiates or marijuana on the immune system have demonstrated that they are receptor mediated, occurring both directly via specific receptors on immune cells and indirectly through similar receptors on cells of the nervous system. Findings are also discussed that demonstrate that cocaine and nicotine have similar immunomodulatory effects, which are also apparently receptor mediated. Finally, the nature and mechanisms of immunomodulation by alcohol are described. Although no specific alcohol receptors have been identified, it is widely recognized that alcohol enhances susceptibility to opportunistic microbes. The review covers recent studies of the effects of these drugs on immunity and on increased susceptibility to infectious diseases, including AIDS.

Cofactors for HIV disease progression in a cohort of homosexual and bisexual men

To evaluate cofactors for progression of HIV infection, the authors identified 370 men with well-defined seroconversion dates and cofactor data among participants in the San Francisco City Clinic Cohort (SFCCC). Postseroconversion substance use, sexual behavior, and sexually transmitted diseases were assessed using multivariate proportional hazards models. Weekly use of hallucinogens strongly and independently predicted death (relative hazard [RH], 2.59; 95% confidence interval [CI], 1.56-4.28), as well as diagnosis of AIDS; weekly cocaine use also predicted mortality. Receptive anal intercourse with ejaculation was independently associated with mortality risk (RH, 1.45; 95% CI, 1.02-2.04) and AIDS. The associations of accelerated progression with weekly use of recreational drugs and unprotected receptive anal intercourse need to be confirmed in other prospective cohorts.

Cocaine inhibits human neutrophil phagocytosis and phagolysosomal acidification in vitro

Cocaine, used intravenously, increases the risk of infections, but its effects on neutrophil phagocytosis have not been examined in vitro. Human neutrophils were suspended in cocaine hydrochloride 0, 1, 10, 50, 100 or 200 microg/ml in Hank's balanced salt solution to which was added a phagocytic meal of killed Saccharomyces cerevisiae stained with the pH indicator dye bromcresol purple. Yeast per phagocytosing neutrophil and the percent neutrophils phagocytosing yeast were reduced in neutrophils treated with cocaine 100 and 200 microg/ml (P < 0.05). When examined for percent of yeast phagocytosed after 10 minutes, neutrophils treated with cocaine 1-200 microg/ml demonstrated a decrease (P < 0.05). However, at 60 minutes only neutrophils treated with cocaine 50 and 100 microg/ml still showed a decrease in percent of yeast phagocytosed. Phagolysosomal acidification was impaired in neutrophils treated with 50, 100 and 200 microg/ml cocaine. Thus, cocaine inhibits neutrophil phagocytosis and phagolysosomal acidification in vitro, offering a reason for cocaine users/abusers to have impaired host defense and to be potentially at higher risk for infections.

In vivo effects of cocaine on immune cell function

Cocaine use has been shown to increase the risk of HIV infection in humans, and this increased risk cannot be explained by i.v. drug use alone. It is thought that this increased susceptibility may be a result of decreased immune responsiveness in cocaine addicts. Scientists are now using animal models to study the effects of cocaine on immune function in vivo under controlled conditions. Many facets of the immune system are being examined, which include immune cell number and distribution, cellular- and humoral-mediated immunity, cytokine production, and immunocompetence to challenges such as infection and tumor growth. The effects of cocaine on many of these functions are not yet clear. Often there are variations in the response of the immune system to cocaine. Potential confounding factors include variations in dose, duration of treatment, and route of administration of cocaine, as well as variations in assay protocols. In addition, there appear to be species differences in immune responses to cocaine. Although it is clear that more research is necessary to resolve the discrepancies, a sufficient number of trends are starting to emerge. This review will systematically evaluate the reported effects of cocaine on immune cell function in vivo. In addition, the possible mechanisms that may be contributing to the immune modulation observed with cocaine in vivo will be addressed. Further, data will be presented describing the effects of cocaine on the autonomic nervous system and the neuroendocrine system suggesting that inhibition of serotonin uptake may be an important component of the overall effects of cocaine on the immune system.