Introduction and Perspectives This volume is based on the proceedings of the 7th annual symposium on the topic Neuroimmune Circuits, Infectious Diseases and Drugs of Abuse, Bethesda, Maryland, Oc- ber 7-9, 1999. This symposium, as in the past, focused on newer knowledge concerning the relationship between the immune and nervous systems with regards to the effects of drugs of abuse and infections, including AIDS, caused by the immunodeficiency virus. Presentations discussed the brain-immune axis from the viewpoint of drugs of abuse rather than from the subject of the brain or immunity alone. The major aim of this series of conferences has been to clarify the consequences of immunomodulation induced by drugs of abuse in regards to susceptibility and pathogenesis of infectious diseases, both in man and in various animal model systems. The recreational use of drugs of abuse such as morphine, cocaine, and marijuana by large numbers of individuals in this country and around the world has continued to arouse serious concerns about the consequences of use of such drugs, especially on the normal physiological responses of an individual, including immune responses. Much of the recent data accumulated by investigators show that drugs of abuse, especially opioids and cannabinoids, markedly alter immune responses in human populations as well as in experimental animals, both in vivo and in vitro.

This volume is based on the Proceedings of the International Conference on "Microbial Infections: Role of Biological Response Modifiers" held in Tampa, FL, May 29-31, 1991. The major purpose of this conference was to bring together in one forum prominent investigators from around the world studying a variety of microbial pathogens, including bacteria, viruses, and fungi, and the effects of biological response modifiers (BRM) on the immune response to these microorganisms. BRM have been widely utilized in the area of antitumor resistance and include not only experimental tumor cell vaccines, but also biologically active substances such as cytokines, i. e., interferons, tumor necrosis factor, and interleukins, as well as products from bacteria which influence host resistance mechanisms. It is the belief of the organizers of this Conference that it was very timely to discuss in detail BRMs as they impact on microbial infections per se. It is now widely accepted that immunocompromised individuals, including those exposed to immunosuppressive substances such as antimetabolites used for chemothera py of malignancies, or infectious agents, such as the human immunodeficiency virus and other viruses which depress the immune response and, in turn, affect a host so as to become highly susceptible to opportunistic microorganisms, benefit from BRM stimulation of their immune system. A wide variety of immunomodulators are now being studied in terms of treating infectious diseases, as well as malignancy and autoimmune diseases."

This volume is based on the program of the International Conference on Drugs of Abuse, Immunity and Immunodeficiency held in Clearwater Beach, Florida. It was sponsored by the University of South Florida College of Medicine with the support of the National Institute on Drug Abuse. During the past few decades, drugs of abuse, including marijuana, cocaine, opiates and alcohol, have been studied by biomedical scientists in terms of the systemic effects of the drugs as well as alterations in neurophysiology and the psychology. More recently, the scope of such investigations has been broadened to include alterations within the immune system, and the influence of altered immunity on physiological and psychological consequences of drug abuse. In this regard, participants in the Clearwater Beach conference provided new information concern ing both basic and clinical aspects of drugs of abuse and immunity, especially immunodeficiency. Advances have been made in recent years in understanding the nature and mechanisms regulating the immune response and the mechanisms by which drugs may influence immune responses. In particular, the emergence of psychoneuroimmunology as a new discipline has heightened interest in immune responses influenced by psychoactive drugs. This has resulted in interdisciplinary investigations involving clinical and basic scientists including microbiologists, immu nologists, physiologists, psychiatrists, oncologists and others. The recreational use of the above mentioned drugs by large numbers of individuals has aroused serious concern about the consequences of this activity.

The use of recreational drugs of abuse by large numbers of individuals in this country and abroad has aroused serious concerns about the consequences of this activity. For example, it is recognized that marijuana is currently widely used as a recreational drug in the United States as well as other countries. Similarly, abuse of cocaine, especially crack cocaine, is considered to be an epidemic. "The war on drugs" by the US Government was directly aimed at the illicit use of cocaine, marijuana, and opiates as well as other drugs of abuse. Furthermore, alcohol is also considered a major problem of abuse in this country as well as in many other countries. It is estimated there are at least 10 million alcoholics in the United States alone. A signi?cant portion of those hospitalized with infectious diseases are alcoholics. Similarly, there have been many reports of association between marijuana use and increased susceptibility to infection as well as a re- tion between use of opiates and infections. The relationship between drug abuse and increased incidence of various infections has stimulated increased investi- tion of whether and how such drugs affect immune function, especially imp- tant for resistance against infectious agents. During the last decades, a wide variety of studies have shown that drugs of abuse, including marijuana, cocaine, or opiates, as well as alcohol, alter both neurophysiological as well as pathological responses of individuals.

The use of recreational drugs of abuse by large numbers of individuals in this country and abroad has aroused serious concerns about the consequences of this activity. For example, it is recognized that marijuana is currently widely used as a recreational drug in the United States as well as other countries. Similarly, abuse of cocaine, especially crack cocaine, is considered to be an epidemic. "The war on drugs" by the US Government was directly aimed at the illicit use of cocaine, marijuana, and opiates as well as other drugs of abuse. Furthermore, alcohol is also considered a major problem of abuse in this country as well as in many other countries. It is estimated there are at least 10 million alcoholics in the United States alone. A signi?cant portion of those hospitalized with infectious diseases are alcoholics. Similarly, there have been many reports of association between marijuana use and increased susceptibility to infection as well as a re- tion between use of opiates and infections. The relationship between drug abuse and increased incidence of various infections has stimulated increased investi- tion of whether and how such drugs affect immune function, especially imp- tant for resistance against infectious agents. During the last decades, a wide variety of studies have shown that drugs of abuse, including marijuana, cocaine, or opiates, as well as alcohol, alter both neurophysiological as well as pathological responses of individuals.

This volume focuses on the relationship between the nervous and the immune system with regard to the effects of drugs of abuse and infections, including infection caused by the immunodeficiency virus which causes AIDS, the number one health problem worldwide. Chapters focus on the brain-immune axis, detailing the effects of drugs of abuse. It is well known that recreational drugs of abuse such as morphine, cocaine, and marijuana, as well as other drugs, including the legal drugs alcohol and nicotine, are used by large numbers of individuals. Serious concerns have been raised about the consequences of using such drugs, especially in relation to their effects on normal physiological responses, including immune mechanisms. It is now widely recognized not only that many drugs of abuse have serious consequences on normal parameters of neurologic and neuroendocrine systems in general but also that effects on those systems, in turn, may affect indirectly immunity and also directly affect immune systems. Much data has now been accumulated showing that drugs of abuse markedly alter the immune response in human populations as well as in experimental animals, both in vivo and in vitro. Furthermore, studies on microbial infections have shown that many drugs of abuse are associated with increased susceptibility to infectious diseases, especially opportunistic intracellular microorganisms, including viruses such as HIV which causes AIDS. The mechanisms whereby drugs of abuse increase the likelihood of infections by opportunistic microorganisms in humans as well as in experimental animals are delineated. This volume will further the understanding of the impact of drugs of abuse on the brain-immuneaxis and its relationship to immunomodulation and infection, especially that caused by the AIDS virus.