Psychoneuroimmunology

Introduction

Psychoneuroimmunology (PNI) is an interdisciplinary field which studies the relationships between neural and endocrine function, and immune processes. More specifically, PNI attempts to elucidate the relations among behavioural and psychosocial factors, nervous, endocrine and immune systems, and health (Ader & Cohen, 1993; Bachen, Cohen & Marsland, 1997).

PNI is a relatively young discipline, though speculations about relationships between mind and body have recurrently been part of Western thought over the centuries. However, it was in the beginning of the last century that several precedents to the scientific study of the interactions between behaviour and immune function began to appear. Particularly, two Soviet researchers, Metalnikov and Chorine, in the 1920s, produced a Pavlovian conditioning of a variety of non-specific defence responses and antibody production in rabbits in response to heat and tactile stimulation as conditioned stimulus (see Ader, 1981 for an historical review of conditioned immunobiological responses). Furthermore, in the 1960s Solomon and Moos (1964) published their paper ‘Emotions, Immunity, and Disease’ which synthesizes the relations of stress, emotions, immunological dysfunction (especially autoimmunity), and physical and mental disease.

Nevertheless, it was in the late 1970s and the beginning of the 1980s, after Ader and Cohen's (1975) seminal work on conditioned modulation of immunity (a great example of scientific serendipity), when PNI was founded.

Psychological Stress and Immunity

One of the most fruitful as well as promising issues in PNI research has been the relationships between stress and immunity. The possible link between neural, endocrine and immune systems deserves particular interest in view of its potential relevance for health maintenance and to its aetiopathogenetic implication in several diseases (Bayés & Borrás, 1999).

A review of the studies which have been carried out on this topic shows that they can be divided into several categories according to different criteria. On the one hand, regarding the population, animal versus human studies. Among human studies, healthy versus non-healthy human subject studies. [Page 775]On the other hand, regarding the type of stress subjects have to cope with, those which explore the effect of chronic stress such as major life events (divorce, bereavement) versus acute stress, such as short-term laboratory stressors (loud noise, unsolvable puzzles) or academic examinations.

Focusing on studies in human beings, the PNI assessment depends on the role of the variables used and the character of the studies. As an interdisciplinary field, as PNI is, it uses assessment instruments and procedures from other disciplines rather than develops its own methods. Generally speaking, it might be distinguished between the procedures for directly assessing the immune function and those for measuring the health status and disease. The first of them are especially useful for healthy population research even though they give some doubts about the clinical relevance of findings. The second offer an approach to disease research though those parameters might be less reliable and present several methodological problems.

The Assessment of Immune Function

The assessment of immune function is made by immunological assays. There are two different types of immunological assays: enumerative and functional assays.