Conditioned manipulation of natural killer (NK) cells in humans using a discriminative learning protocol

Psycho-Neuro-Endocrine-Immunological Basis of the Placebo Effect: Potential Applications beyond Pain Therapy

The placebo effect can be defined as the improvement of symptoms in a patient after the administration of an innocuous substance in a context that induces expectations regarding its effects. During recent years, it has been discovered that the placebo response not only has neurobiological functions on analgesia, but that it is also capable of generating effects on the immune and endocrine systems. The possible integration of changes in different systems of the organism could favor the well-being of the individuals and go hand in hand with conventional treatment for multiple diseases. In this sense, classic conditioning and setting expectations stand out as psychological mechanisms implicated in the placebo effect. Recent advances in neuroimaging studies suggest a relationship between the placebo response and the opioid, cannabinoid, and monoaminergic systems. Likewise, a possible immune response conditioned by the placebo effect has been reported. There is evidence of immune suppression conditioned through the insular cortex and the amygdala, with noradrenalin as the responsible neurotransmitter. Finally, a conditioned response in the secretion of different hormones has been determined in different studies; however, the molecular mechanisms involved are not entirely known. Beyond studies about its mechanism of action, the placebo effect has proved to be useful in the clinical setting with promising results in the management of neurological, psychiatric, and immunologic disorders. However, more research is needed to better characterize its potential use. This review integrates current knowledge about the psycho-neuro-endocrine-immune basis of the placebo effect and its possible clinical applications.

Effects of oxytocin administration and conditioned oxytocin on brain activity: An fMRI study

It has been demonstrated that secretion of several hormones can be classically conditioned, however, the underlying brain responses of such conditioning have never been investigated before. In this study we aimed to investigate how oxytocin administration and classically conditioned oxytocin influence brain responses. In total, 88 females were allocated to one of three groups: oxytocin administration, conditioned oxytocin, or placebo, and underwent an experiment consisting of three acquisition and three evocation days. Participants in the conditioned group received 24 IU of oxytocin together with a conditioned stimulus (CS) during three acquisition days and placebo with the CS on three evocation days. The oxytocin administration group received 24 IU of oxytocin and the placebo group received placebo during all days. On the last evocation day, fMRI scanning was performed for all participants during three tasks previously shown to be affected by oxytocin: presentation of emotional faces, crying baby sounds and heat pain. Region of interest analysis revealed that there was significantly lower activation in the right amygdala and in two clusters in the left superior temporal gyrus in the oxytocin administration group compared to the placebo group in response to observing fearful faces. The activation in the conditioned oxytocin group was in between the other two groups for these clusters but did not significantly differ from either group. No group differences were found in the other tasks. Preliminary evidence was found for brain activation of a conditioned oxytocin response; however, despite this trend in the expected direction, the conditioned group did not significantly differ from other groups. Future research should, therefore, investigate the optimal timing of conditioned endocrine responses and study whether the findings generalize to other hormones as well.

Pavlovian Conditioning of Immunological and Neuroendocrine Functions

The phenomenon of behaviorally conditioned immunological and neuroendocrine functions has been investigated for the past 100 yr. The observation that associative learning processes can modify peripheral immune functions was first reported and investigated by Ivan Petrovic Pavlov and his co-workers. Their work later fell into oblivion, also because so little was known about the immune system’s function and even less about the underlying mechanisms of how learning, a central nervous system activity, could affect peripheral immune responses. With the employment of a taste-avoidance paradigm in rats, this phenomenon was rediscovered 45 yr ago as one of the most fascinating examples of the reciprocal functional interaction between behavior, the brain, and peripheral immune functions, and it established psychoneuroimmunology as a new research field. Relying on growing knowledge about efferent and afferent communication pathways between the brain, neuroendocrine system, primary and secondary immune organs, and immunocompetent cells, experimental animal studies demonstrate that cellular and humoral immune and neuroendocrine functions can be modulated via associative learning protocols. These (from the classical perspective) learned immune responses are clinically relevant, since they affect the development and progression of immune-related diseases and, more importantly, are also inducible in humans. The increased knowledge about the neuropsychological machinery steering learning and memory processes together with recent insight into the mechanisms mediating placebo responses provide fascinating perspectives to exploit these learned immune and neuroendocrine responses as supportive therapies, the aim being to reduce the amount of medication required, diminishing unwanted drug side effects while maximizing the therapeutic effect for the patient’s benefit.

Learned Placebo Effects in the Immune System

Associative learning processes are one of the major neuropsychological mechanisms steering the placebo response in different physiological systems and end organ functions. Learned placebo effects on immune functions are based on the bidirectional communication between the central nervous system (CNS) and the peripheral immune system. Based on this “hardware,” experimental evidence in animals and humans showed that humoral and cellular immune functions can be affected by behavioral conditioning processes. We will first highlight and summarize data documenting the variety of experimental approaches conditioning protocols employed, affecting different immunological functions by associative learning. Taking a well-established paradigm employing a conditioned taste aversion model in rats with the immunosuppressive drug cyclosporine A (CsA) as an unconditioned stimulus (US) as an example, we will then summarize the efferent and afferent communication pathways as well as central processes activated during a learned immunosuppression. In addition, the potential clinical relevance of learned placebo effects on the outcome of immune-related diseases has been demonstrated in a number of different clinical conditions in rodents. More importantly, the learned immunosuppression is not restricted to experimental animals but can be also induced in humans. These data so far show that (i) behavioral conditioned immunosuppression is not limited to a single event but can be reproduced over time, (ii) immunosuppression cannot be induced by mere expectation, (iii) psychological and biological variables can be identified as predictors for this learned immunosuppression. Together with experimental approaches employing a placebo-controlled dose reduction these data provide a basis for new therapeutic approaches to the treatment of diseases where a suppression of immune functions is required via modulation of nervous system-immune system communication by learned placebo effects.

Learned placebo responses in neuroendocrine and immune functions

The phenomenon of learned placebo responses in neuroendocrine and immune functions is a fascinating example of communication between the brain and both the endocrine and peripheral immune systems. In this chapter, we will give a short overview of afferent and efferent communication pathways, as well as the central mechanisms, which steer the behavioral conditioned immune response. Subsequently, we will focus on data that provides evidence for learned immune responses in experimental animals and learned neuroendocrine and immune placebo responses in humans. Finally, we will take a critical look at these learning protocols, to determine whether or not they can be considered a viable additional treatment option to pharmacological regimens in clinical routine. This is fundamental, since there are still a number of issues, which need to be solved, such as the potential reproducibility, predictability, and extinction of the learned neuroendocrine and immune responses. Together, these findings not only provide an excellent basis to increase our understanding of human biology but may also have far reaching clinical implications. They pave the way for the ultimate aim of employing associative learning protocols as supportive treatment strategies in pharmacological regimens. As a result, medication levels may be reduced, as well as their unwanted side effects, providing a maximized therapeutic outcome to the benefit of the patient.

The learned immune response: Pavlov and beyond

The ability to associate physiological changes with a specific flavor was most likely acquired during evolution as an adaptive strategy aimed at protecting the organism while preparing it for danger. The behaviorally conditioned or learned immune response is an exquisite example of the bidirectional communication between the central nervous system (CNS) and the peripheral immune system. How is it possible that specific immuno-modulating properties of a drug or substance (unconditioned stimulus) can be re-enlisted just by the mere re-exposure to a particular taste, odor or environment (conditioned stimulus)? To answer this key question, we review the neurobiological mechanism mediating this type of associative learning, as well as the pathways and mechanisms employed by the brain to harness the immune system during the execution of the conditioned immune response. Finally, we focus on the potential therapeutic relevance of such learned immune responses, and their re-conceptualization within the framework of "learned placebo effects".

Recent findings on the pathogenesis of bronchial asthma. Part II. The role of hormonal predisposition, environmental influences and conditioning leading to bronchial asthma

In this second part of the review on the pathogenesis of asthma the hormonal factors and adverse external events are shortly reviewed which skew the balance of Th1 vs. Th2 CD4+ lymphocytes towards the latter ones and this way increase the probability of atopic diseases. Among other the role of transplacental priming, insulin, insulin-like and other growth factors, lack of the usual microbial infections in the early childhood (the so-called hygiene hypothesis), gender, diminished testosterone production, gastroesophageal reflux, adverse effects during pregnancy are discussed. A separate chapter deals with the role of central nervous system in the etiology and finally the most common allergizing and airway tissue damaging agents are listed in tabulated form.

Expectations and associations that heal: Immunomodulatory placebo effects and its neurobiology

The use of placebo may have accompanied healing and medical practices since their origins (Plato; Charmides, 155-156). Recent experimental data indicate that we would be well advised to further consider placebo effects in future therapeutic strategies, with a better knowledge of their potency, psychological basis and underlying neurobiological mechanisms. Current research in the areas of pain, depression and Parkinson's disease has uncovered some of the potential neurobiological mechanisms of placebo effects. These data indicate that conscious expectation and unconscious behavioral conditioning processes appear to be the major neurobiological mechanisms capable of releasing endogenous neurotransmitters and/or neurohormones that mimic the expected or conditioned pharmacological effects. To date, research on placebo responses affecting immune-related diseases is scarce, but there are consistent indications that skin and mucosal inflammatory diseases, in particular, are strongly modulated by placebo treatments. However, the brain's capability to modulate peripheral immune reactivity has been impressively demonstrated by paradigms of behavioral conditioning in animal experiments and human studies. Thus, placebo effects can benefit end organ functioning and the overall health of the individual through positive expectations and behavioral conditioning processes.

Pavlovian conditioning of opioid and nonopioid pain inhibitory mechanisms in humans

Learning processes such as respondent or Pavlovian conditioning are believed to play an important role in the development of chronic pain, however, their influence on the inhibition of pain has so far not been assessed in humans. The purpose of this study was the demonstration of Pavlovian conditioning of stress-induced analgesia in humans and the determination of its opioid mediation. In a differential classical conditioning paradigm two different auditory stimuli served as conditioned stimuli and mental arithmetic plus white noise as unconditioned stimulus. Subsequent to four conditioning trials naloxone or placebo was applied in a double-blind fashion on two test days. Both pain threshold and pain tolerance showed conditioned stress-induced analgesia. Pain tolerance was affected by naloxone whereas pain threshold was not. The data of this study show that stress analgesia can be conditioned in humans and that it is at least partially mediated by the endogenous opioid system. Learning processes also influence pain inhibitory processes in humans and this effect might play a role in the development of chronic pain.

Conditioned inhibition of cyclophosphamide-induced taste aversion

Rats in an experimental group received trials during which 1 flavor (saccharin) was always followed by cyclophosphamide, an immunosuppressive drug, but another (vanilla) was not. An unconditioned stimulus-only group served as a control. Flavor-preference tests revealed that conditioned excitation and conditioned inhibition occurred in the conditioned group subjects but not in the control group subjects. This demonstration suggests that a conditioned inhibitor might be used to modify conditioned and unconditioned immune system functions, for example, natural killer-cell activity.

Psychological interventions and the immune system: a meta-analytic review and critique

This article reviews evidence for the hypothesis that psychological interventions can modulate the immune response in humans and presents a series of models depicting the psychobiological pathways through which this might occur. Although more than 85 trials have been conducted, meta-analyses reveal only modest evidence that interventions can reliably alter immune parameters. The most consistent evidence emerges from hypnosis and conditioning trials. Disclosure and stress management show scattered evidence of success. Relaxation demonstrates little capacity to elicit immune change. Although these data provide only modest evidence of successful immune modulation, it would be premature to conclude that the immune system is unresponsive to psychological interventions. This literature has important conceptual and methodological issues that need to be resolved before any definitive conclusions can be reached.

Pavlovian conditioning of immune function: animal investigation and the challenge of human application

Pavlovian conditioning of immune functions provided early impetus to the rapidly expanding knowledge of bi-directional communication among the immune, endocrine, and central nervous systems. Since these early investigations, the phenomenology of this response has been well characterized. However the neural mechanisms and biological relevance of conditioned immunomodulation remain unclear. To this end, we present here data from our laboratories that have: (1) revealed some of the neural mechanisms and biological relevance of an animal model of conditioned immunomodulation; (2) demonstrated the conditionability and potential mechanisms of conditioned immune responses in healthy humans, and (3) investigated conditioned immunomodulation in a clinical sample. Together, these data demonstrate that animal models provide a basis for investigating mechanisms whereby conditioned changes in immune function may modulate health status in a clinical realm.

Conditioned immune response to interferon-gamma in humans

We determined whether a classical conditioning paradigm may be used to condition immunologic responses in normal human subjects receiving an optimal immunostimulating dose of recombinant human interferon-gamma (rhIFN-gamma). We conducted a placebo-controlled, double-blind study of 31 normal volunteers in order to determine whether an initially immune-neutral stimulus, oral propylene glycol (PG), could eventually elicit an immune response as a consequence of its being paired with a known immunostimulatory dose and schedule of rhIFN-gamma. Subjects were randomly assigned to one of three groups: (A) rhIFN-gamma injections paired with PG; (B) normal saline injections paired with PG; (C) rhIFN-gamma injections alone. During the 4-week study, subjects received progressively fewer injections so that, by the final week of the study, no injections were given and groups A and B received only PG. The principal outcome measures were serum concentrations of quinolinic acid (QUIN) and neopterin, two nonspecific but sensitive markers of immune activation, and expression of Fc receptors (CD64) on peripheral blood mononuclear cells. RhIFN-gamma injections produced significant and predictable alterations in each of the measured immune parameters. No group B subject made an immune response. Mean serum QUIN levels were significantly higher at the end of week three for subjects in the experimental condition (group A) than for subjects receiving rhIFN-gamma alone (group C) despite receiving identical doses of rhIFN-gamma. Similarly, the predicted decay in mean serum neopterin levels from the end of week 1 to the end of week 2 was seen in group C but not in group A. The exposure of group A to PG blunted the decline of CD64 expression in week four. The data suggest that the pairing of an unconditioned stimulus (rhIFN-gamma) and a conditioned stimulus (PG) permits the conditioned stimulus alone to prolong a cytokine-induced response in normal humans.