Interactions between the immune and nervous systems in human health

Immune Biopsychology

Interactions of the Human Immune System and Nervous System and their Implications on Biopsychology

This paper presents information obtained through a review of current knowledge and literature in the areas of immune system response and general nervous system functioning in the human body, and the interactions and influences that exist between these two systems. A general understanding of the immune system and some of its constituent arts its provided as necessary background information, as is a brief explanation of the nervous system and its functions in the body. A broad understanding of these systems and the mechanisms by which they function provides initial knowledge and a framework for examining the interactions that occur between these two systems and their effects on each other. These interactions are then discussed form a biopsychological perspective, noting the relationship that exists not only between mental and physiological health, but the physiological creation of (or at least influence of) mental health through such interactions.

Introduction

The human immune system is comprised of complex interactions of various cells, organs, and organ systems, coordinated through a variety of chemical and electronic messages that are in a constant state of transmittal. As the different mechanisms that protect the human body from both disease-causing foreign agents and internal stresses that reach less-than-optimal levels engage, other elements of human physiology and psychology are impacted upon, creating a complex cascade of often cyclical effects on the body and mind.

The nervous system is also highly complex n the variety of tasks it performs and in its extent throughout the body, though it is somewhat more straightforward than the immune system in terms of the basic activities it performs and the mechanisms by which it functions. Essentially serving as the communications network for the body in virtually all of its functions and actions, the nervous system has tremendous effects on the workings of other systems, and is generally instrumental in the continued functionality of every organ and organ system throughout the body. Because of this, damage to the nervous system or simple mis-firings in the vast array of its neurons on neurotransmitters can lead to a variety of issues in other systems throughout the body, including the immune system. Similar issues can occur in reverse, with damage to other organs or organ systems leading to nervous system disorders or symptoms. These interactions can have further impacts on the overall psychological as well as physiological health of the individuals that must deal with these situations.

Direct interactions between the nervous and immune systems of the human body are especially likely to have an impact on the physiological and psychological health of a given individual. Anecdotal evidence linking mood and other psychological features with certain diseases and symptoms has existed in most reputable medical texts since ancient times, and modern research continues to support many similar conclusions from a more objective and empirical perspective. As the mechanisms of the nervous system and the human immune system are investigated further and better understood, knowledge in this area continues to become more refined.

Biopsychology is a relatively new field of psychology and medicine, and attempts to pinpoint the physiological and neurological mechanisms that contribute to and/or create psychological temperaments and disorders. Understanding how the nervous system operates in a manner that influences consciousness, and understanding the many different factors that can have an effect on the nervous system, constitute the primary research questions that the field of biopsychology is concerned with; the ways in which the physiological workings of the body and mind affect the psychological perspectives, attitudes, and functions of an individual are of direct and explicit interest to researchers in this field. Developing such understandings can lead to better diagnostic indicators for physiological disorders and symptoms as well as producing better understandings of and treatments for many psychological issues and disorders, improving knowledge and practice in both physical medicine and often less-concrete psychological undertakings through the careful and rigorous examination of their common elements, influences, and mutual interactions.

This paper examines a broad array of literature in order to develop a better understanding of the interactions that occur between the human immune system and the nervous system, and the relationships that these many complex and multidirectional interactions have on biopsychology. Beginning with an overview of the immune system, followed by one of the nervous system, the broad interactions between these two systems are then presented, with several specific examples of interactions explored and analyzed as examples.

Following this examination of the ways in which the nervous and immune systems interact within the human body, the ultimate implications of these interactions in the field of biopsychology are examined and detailed. Though many of these implications and the overall biopsychological context of the phenomena and mechanisms discussed are apparent throughout the examination of current literature contained herein, this explicit discussion of biopsychology and its influence by the interactions between the nervous and immune systems is useful for its collation and coordination of the data and conclusions encountered in a broader review of current literature. By progressing from independent overviews of specifics aspects of the research question to a cohesive and comprehensive analysis of the query and resultant information as a whole, it is hoped that this paper will provide insight into the development and implications of the biopsychological perspective as it is applied practically and theoretically.

The Nervous System

The nervous system is much more simply explained than the immune system, at least in a superficial sense, though its effects and ramifications throughout the body are at times highly complex and entirely pervasive. With the brain as the primary source of direct instruction to other organs and systems, and the primary receiver of information from other areas of the body, the nervous system provides communication throughout the body. It is through the functioning of the nervous system that external and internal elements and changes can be responded to in both conscious and unconscious manners in order to (generally) maintain health and homeostasis.

Like the immune system, the nervous system is in a constant state of evolution, development, and reaction throughout life (Michigan 2002). Certain things occur on a conscious or from-conscious level -- the nervous system is involved in transmitting the images of words from the page to the brain where they are deciphered as one purposefully reads, and the muscles controlling the hand and fingers are fires as one turns the page -- and other functions are carried out wholly subconsciously, such as the actually focusing of the eyes and the control of the pupil size based on distance and light, respectively. The full array of bodily functions, from the continued beating of one's heart to the contraction of muscles in the digestive tract and all reaction to -- and indeed notice of -- sensory input, all depend on the proper and continued functioning of the nervous system. This means that disruptions to the nervous system can be hugely influential in the functioning of other bodily systems and functions.

Also like the immune system, though along very different lines, the basic architecture of the nervous system is divided into two parts. The central nervous system is made up of the brain and the spinal cord -- a bundle of nerves running through the spinal column; these two organs are responsible for originating, coordinating, and disseminating most communications throughout the body (Ophardt 2003). Specific chemical messengers, called neurotransmitters, travel between nerve cells in the brain in a cascade action that produces electrical current and triggers other nearby neurons in a highly specific manner, producing the (generally) desired actions and adjustments in the body and its functions (Ophardt 2003).

The nerves running from the central nervous system, i.e. The spinal cord, to the many organs and muscles of the body, constitutes the second part of the nervous system's basic architecture, and is known as the peripheral nervous system (Michigan 2002). While there are different types of cells in the central nervous system, particularly in the brain, the peripheral nervous system is composed only of nerves -- bundles of neurons, which are used only for the transmission of electric impulses through certain chemical chain reactions and cascade effects (Farabee 2001; Ophardt 2003). The central nervous system contains both neurons and specialized glial cells that insulate and protect neurons in the brain; some similar functions are provided by the myelin sheaths that surround neurons in the peripheral nervous system (Farabee 2001). These myelin sheaths not only protect the nerve cells, but they also serve as electronic insulators, increasing the speed of transmission of the signals sent both towards and away from the brain throughout the nervous system (Michigan 2002; Farabee 2001).

Given the nervous systems spread and relative simplicity, it is fairly easy to see how issue sin the nervous system would have major impacts on the functioning of other organ systems, including the immune system. On the other hand, as the immune system operates largely via chemical messengers in the blood and lymph systems, bypassing much of the communication network that is the nervous system, the interactions between these two essential organ systems in the human body are not entirely obvious or straightforward. An examination of the specifics of these interactions makes it clear how intertwined their workings truly are.

Key Interactions Between the Nervous and Immune Systems

There are many direct and indirect ways in which he workings of the nervous system can affect those of the immune system and vice versa. Some of these interactions result in specific disorders, diseases, or adverse symptoms developing, and are generally undesirable yet serve to advance medical knowledge and science as they are better understood. Other interactions are actually directly supportive of the functionality of one or the other or even both systems. Regardless of the purposefulness of the interactions that occur or the ultimately positive or negative effects of that interaction, most of the influence that the nervous and immune systems wield over each other come from crossovers in the communications networks for the two systems that are not really as discrete as they initially appear.

One of the ways in which these systems interact, it has been found, is in the partial regulation of T-cell presence and activity by the nervous system. A specific peptide -- one of many types of chemical messengers -- that has long been known to stimulate neuronal activity and serve as a regulator for neuron survival, also mediates the survival of Th1 and Th2 cells, two different types of T-cells with varying functions (UCSF 2001). Blocking receptors for this peptide results in a disproportionate amount of Th1, which redistributes the immune system's resources in a way that makes it fight pathogenic infection much harder, while leaving it more vulnerable to parasitic organisms and certain other health issues (UCSF 2001). This interaction is already being heavily explored as a method of treating certain infections and autoimmune disorders (UCSF 2001).

Such a reordering of the immune system's resources can occur on a much more extensive and profound level due to certain other issues affecting the nervous system, including conscious though uncontrollable emotional issues. Studies have revealed that certain stressors, especially major catastrophic incidents, can lead to major overall drops in the number of T-cells within an organism, and to the overall functionality and efficiency of the immune system (Shomon 2010). Stress can cause the release of adrenal hormones, which shift the body's energy to immediate usefulness at the expense of systems such as the immune system; the nervous system effectively slows all immediately unnecessary processes (Shomon 2010). More intriguing still is the fact that certain macrophages and lymphocytes that roam the body in search of antigens have actually been found to secret certain neuropeptides, activating both other immune cells and cells within the nervous system to create further signals for immune activity, instigating a self-responsive neural and immune response to specific situations (Shomon 2010).

The interactions between these two systems can also occur in the opposite direction, with immune responses having an effect on the workings of the nervous system. The secretion of certain cytokines by immune system cells, for instance, has been found to activate the secretion of neural hormones and messengers in the hypothalamus, pituitary, and adrenal glands, thus stimulating specific neuronal activity based on the fact that an infection has been encountered (Dunn 2000). Just as issues that directly affect the nervous system affect other functions and systems indirectly, an immune response changes the way in which all of the functions of the body are coordinated.

These interactions are but a few of the many different ways in which the nervous systems and the immune systems of the human body interact with each other. These interactions ultimately all take place on molecular and chemical levels, with communication between the nervous and immune systems more extensive than previously thought due to the presence and secretion of many different chemical messengers by both systems that have direct and apparently purposeful effects on the other system (Dunn 2000; Shomon 2010). These molecular interactions are responsible for large scale changes in both physiology and temperament, making the interactions between the nervous and immune systems a matter of great importance not simple in direct physical medicine but also in psychology.

Implications for Biopsychology

What this means, in essence, is that there is a significant biopsychological element to the interactions that occur between the nervous and immune systems. The workings of the body necessarily affect certain psychological outcomes, with this relationship becoming more clear as the causes originating in the body become more extreme. The influence of the immune system on the nervous system, and vice versa, demonstrated the degree to which the mental/nervous workings of a person are related to their health, and even more specifically to their bodies' attempts at retaining health. Though the direct purpose for many of the biophysical impacts that the nervous and immune systems have is unknown, these impacts can have both positive and negative psychological outcomes overall.

The effect of stress and other psychological pressures on the immune system as noted above is one major area of biopsychological impact brought about by the interaction of the nervous and immune systems. Not only do major stressors such as a death or a major life change create a hormonal shift that limits the efficiency and effectiveness of the immune system, but ongoing stress created by certain personality types can also lead to an increased likelihood for the development of more common and more extreme illnesses than individuals with a more low-key temperament (Hall, Stanton, & Schultheiss 2010). Essentially, individuals who are more motivated by power tend to show an increased vulnerability to illness and a generally reduced immune system functionality due to the ongoing activation of their sympathetic nervous system -- i.e. that which is activated by stress, fear, and other survival-instinct related events and environments -- that they experience (Hall et al. 2010).

Stress in childhood might also explain the recent "epidemic" rise in allergies among children in the United States specifically and the developed world generally. The hypothalamus-pituitary-adrenal hormonal network that is so influential in the workings of the nervous system can be affected by stress, it is known, and these effects have been correlated (though not causally linked, as of yet) to allergy development in children (Buske-Kirschbaum 2009). Overproduction of Th2 cells can lead to allergy development, as well, and it is possible that the stress hormones released by the HPA axis somehow disturbs the balance of T-cells in an ongoing fashion, meaning early psychological issues can cause life-long health problems (Buske-Kirschbaum 2009).

In addition to the effects of stress on the immune system, a very common area of investigation in biopsychology/immunology research has been the level of correlation between various psychopathologies and personalities, or the predispositions to certain illnesses and disorders that certain psychological and personality elements seem to lead to (Coe & Laudenslager 2007). The manner in which an individual is raised has a great deal to do with that person's personality development and overall psychological outlook, according to most theories, and this in turn can have a great deal of influence over the eventual development and overall efficacy of their immune system (Coe & Laudenslager 2007). According to some studies, specific psychological issues can result in reorganizations in the function of the immune system, leaving certain individuals more prone to specific types of infection and allergies or other immune deficiencies (Coe & Laudenslager 2007).

In addition to having detrimental effects on immune response and immune system efficacy over the long-term, positive psychological outlooks and responses can also have positive medical and immunological benefits. In a study of patients with a certain type of cancer, survival was increased by over six months on average based on scores of posttraumatic growth (Dunigan, Carr, & Steele 2007). All patients received the same treatment, but regardless of the different direct responses to these treatments, recovery was faster and survival was longer in patients that scored higher on this PTG inventory than for those with lower scores on the test, indicating a direct link between psychological outlook and immune response (Dunigan et al. 2007).

Conclusion

The immune system and the nervous system are both highly complex networks of different organs that interact amongst themselves and with each other via different chemical messengers. The systems operate with very different functions, and so in a way that is -- or at least appears to be -- largely independent of each other. The similarities and downright duplications of the chemical messengers used in both systems, however, makes their functions and their developments inextricably linked to each other. The interactions between these two systems can have major influences on an individual's conscious outlook on life as well as their overall health and the trajectory of their development, in both physiological and psychological ways that can be quite profound and incredibly persistent in their effects.

The biopsychological effects of the interactions between the nervous and immune systems in the human body can be especially persistent, lasting throughout life in many cases. Changes in the way that the body processes information, whether brought about though normal development, sudden trauma, or isolated incidents of stress, can all have an effect on the body's ability to fend off disease, just as fending off infections and other threats of disease can have an effect on one's psychological outlook and personality, both temporarily and on a more ongoing basis. As the biopsychological relationship between the nervous and immune systems becomes better understood, new methods for treatment and suggestions for care continue to emerge.