Blocking and Unblocking in Human Causal Learning

Three experiments sought to develop the suggestion that, under some circumstances, common associative learning mechanisms might underlie animal conditioning and human causal learning, by demonstrating, in humans, an effect analogous to the unblocking by reinforcer omission observed in animal conditioning. Experiment 1 found no such effect. Experiment 2, designed to prevent inhibitory influences that might have masked excitatory unblocking in Experiment 1, demonstrated unblocking, indicating common human-animal associative learning mechanisms in which the associability of a stimulus varies as a function of its predictive history. Experiment 3, using a similar design but with a procedure promoting application of rational inference processes, failed to detect the same unblocking effect, indicating that associative and cognitive mechanisms may influence human causal learning.

Influences of distress and alcohol consumption on the development of a delayed-type hypersensitivity skin test response

OBJECTIVE

This paper reports the effects of naturally occurring levels of distress on the development of delayed-type hypersensitivity (DTH) skin test responses. These in vivo measures provide a biologically relevant assessment of cellular immune competence.

METHODS

Subjects (N = 166) were immunized (baseline) with the novel antigen, keyhole limpet hemocyanin (KLH), and DTH skin test responses against KLH were assessed 3 weeks later (follow-up). The CMI Multitest (Merieux, France), which evaluates DTH responses to a panel of seven antigens, was also administered at follow-up. Emotional distress was assessed at baseline and follow-up by the Profile of Mood States.

RESULTS

Distress levels at baseline were associated with a reduced likelihood of developing DTH responses against KLH at follow-up (r = -0.22, p =.01). There was no relationship between distress at follow-up and cutaneous DTH in response to KLH (r = 0.09, p =.24) or in the Multitest (r = -0.03, p =.70). In addition, higher levels of alcohol consumption at baseline (r = -0.19, p =.02) and at follow-up (r = -0.20, p =.01) were associated with a decreased likelihood of developing cutaneous DTH against KLH.

CONCLUSIONS

Everyday levels of distress predicted the capacity of the cellular arm of the immune system to exhibit recall responses to an antigen, when the experimental paradigm allowed the assessment of distress at the time of antigen sensitization. Moderate alcohol consumption independently affected cutaneous DTH.

Effects of confinement (110 and 240 days) on neuroendocrine stress response and changes of immune cells in men

The aim of the study was to evaluate the effects of long-term confinement on stress-permissive neuroendocrine and immune responses in humans. Two groups of four male subjects were confined 240 days (group 240) or 110 days (group 110) in two space modules of 100 or 200 m3, respectively. During confinement, none of the volunteers developed psychic stress as could be examined and verified by a current stress test. However, in group 240 but not in group 110, the diurnal rhythm of cortisol secretion was slightly depressed and the urine excretion of norepinephrine significantly increased. The innate part of the immune system became activated as seen by a rise in the number of circulating granulocytes and the enhanced expression of beta2-integrins. In contrast, the ratio of T-helper to T-suppressor cells decreased. All these effects, observed during confinement, were even more pronounced in both groups when values of endocrinological and immunological parameters were compared between before and 1 wk after the end of the confinement period. Hence, return to normal life exerts pronounced effects to a much higher degree, irrespective of how long or under which conditions individuals were confined. Because the delayed-type hypersensitivity skin reaction against recall antigens remained unaffected, it is to be presumed that confinement appears to induce distinct sympathoadrenergic activation and immunological changes but no clinically relevant immunosuppression.

Socially inhibited individuals show heightened DTH response during intense social engagement

To determine whether altered cellular immune response might mediate the increased health risks associated with social inhibition, we examined delayed type hypersensitivity (DTH) responses in 36 adults under conditions of low and high intensity social engagement. Participants come from a study of psychological factors in functional bowel disease and fibromyalgia. Under high engagement conditions, socially inhibited individuals showed significantly increased induration in response to intradermal tetanus toxoid. Under low engagement conditions, these individuals showed less pronounced DTH responses that did not differ in magnitude from those of uninhibited individuals. This pattern of results was found using two different measures of social inhibition and was independent of social inhibition's definition as a continuously distributed trait vs a discrete category. These data are consistent with the general hypothesis that social inhibition represents a predisposition to physiologic hyperresponsiveness that requires an exogenous social trigger for expression.

Effects of relaxation on the delayed-type hypersensitivity (DTH) reaction to diphenylcyclopropenone (DCP)

Delayed-type hypersensitivity (DTH) reactions to the experimental allergen diphenylcyclopropenone (DCP) were measured in four groups, which either trained (+) or did not train in relaxation (-) during the sensitization and/or the challenge phase. All groups consisted of high and low hypnotic susceptible subjects. While there were no differences in erythema, the mean induration of the group which trained in relaxation in both the sensitization and the challenge phase (+/+) was significantly greater than that of the group which trained in relaxation in the challenge phase only (-/+). Significant correlations were found between induration and hypnotic susceptibility scores, and between induration and degree of perceived relaxation during challenge. High hypnotic susceptible subjects experienced a higher degree of perceived relaxation and exhibited greater indurative and erythematous DTH reactions to DCP than low hypnotic susceptible subjects in all four experimental conditions. Though the mediating mechanisms remain unclear, our results suggest that relaxation may affect the DTH reaction, and support previous findings of higher psychophysiologic reactivity of high hypnotic susceptible subjects.

The assessment of the emotional and immunological consequences of examination stress

Sixteen final-year students and 14 nonstudents were recruited into a pilot study exploring the utility of the Merieux Multitest CMI in identifying stress-related immune impairment. The results of the investigation revealed that the examination group reported greater stress than the nonexamination group. The relationship between stress and immune impairment was explored using two widely held definitions of stress (i.e., stimulus and response). When stress was defined as the stimulus (i.e., examination versus nonexamination groups), reactions to the skin test were not significantly different. However, when stress was defined as the response (i.e., high stress versus low stress scores), the high-stress individuals were found to have poorer reactions to the skin test than the low-stress subjects. The results of the study highlight the need for greater precision in the definition of the term stress and, also, suggest that Multitest CMI can provide a rapid and reproducible means of assessing stress-related immune dysfunction.

Biochemical correlates of in vivo cell-mediated immune dysfunction in patients with depression: a preliminary report

We have previously demonstrated that at least 50% of patients with melancholia have impaired cell-mediated immunity (CMI) as assessed by delayed-type hypersensitivity (DTH) skin responses to a standardized battery of antigens. Hypercortisolaemia and increased circulating catecholamines both occur in patients with severe depressive disorders and each has been proposed as a possible mediator of observed immune abnormalities in patients with mood disorders. As part of a larger study, we collected 24 h urine samples from 28 patients with major depression and measured concentrations of urinary free cortisol (UFC), the noradrenaline metabolite dihydroxyphenylglycol (DHPG), adrenaline, and the dopamine metabolite DOPAC. CMI multitest skin testing revealed a reduced or absent response in 54% of subjects. Those with reduced DTH skin responses demonstrated increased urinary adrenaline (P < 0.02), with trends toward increased UFC (P = 0.052) and increased DHPG (P = 0.06). These differences could not be attributed to differences in age or depression severity. Correlational analyses demonstrated inverse associations between the extent of DTH responsiveness and 24 h levels of urinary adrenaline and DHPG, with similar trends evident for UFC and DOPAC. These results suggest that both circulating catecholamines and cortisol may play roles in the reduction of CMI in patients with severe depression.

Cell-mediated immune function and the outcome of chronic fatigue syndrome

This study examined the importance of cell-mediated immunity in determining the long-term outcome of patients diagnosed with chronic fatigue syndrome (CSF). A total of 103 patients (74%) of 139 previously enrolled in one of two treatment trials conducted within a university hospital referral center was reviewed a mean of 3.2 yr after trial entry. Ongoing symptom severity, levels of disability and immunological function were assessed at follow-up. The relationship between immunological function at trial entry and measures of outcome was also evaluated. Sixty-five patients (63%) had improved, while only 6 (6%) reported no current symptoms. Thirty-one subjects (30%) were unable to perform any form of work and 26 (25%) were on a disability benefit directly attributable to CFS. Cell-mediated immune function, as measured at trial entry or follow-up, did not appear to affect outcome. Whilst improvement occurred in the majority of patients with CFS, a substantial proportion (37%) remained functionally impaired. Impairment of cell-mediated immunological function measured during the course of the illness may not be an important factor in determining long-term outcome.

Effect of hypnotic suggestion on the delayed-type hypersensitivity response

OBJECTIVE

To determine whether individuals selected for good general health, high hypnotizability, and the ability to alter skin temperature under hypnotic suggestion can influence the delayed-type hypersensitivity (DTH) response to varicella-zoster (VZ) antigen under hypnotic suggestion.

DESIGN

A blinded clinical trial using a repeated measures design with subjects serving as their own controls. Subjects were randomly assigned to undergo a predetermined sequence of four different experimental conditions, occurring at weekly intervals, with each condition including VZ skin testing: (1) hypnosis with suggestions to enhance the DTH response to VZ antigen; (2) hypnosis with suggestions to suppress the DTH response; (3) hypnosis with suggestions for relaxation only; and (4) skin testing without hypnosis.

SETTING

A National Institutes of Health-supported clinical research center in a teaching hospital.

SUBJECTS

A stratified sample of 24 ambulatory, healthy, highly hypnotizable, volunteer college students selected for their above-average ability to alter skin temperature after hypnotic suggestions and their positive baseline responses to VZ antigen. There were 11 males and 13 females with a mean +/- SD age of 22 +/- 6 years. The mean +/- SD hypnotizability score (Harvard Group Scale of Hypnotic Susceptibility) was 11 +/- 1.

INTERVENTIONS

Intradermal skin testing with VZ antigen (Mantoux method) and hypnotic suggestion.

MAIN OUTCOME MEASURES

Areas of induration of the DTH response measured at 24 and 48 hours after injection of antigen.

RESULTS

The area of the DTH response was not affected by the experimental interventions. The area of erythema was likewise unaffected.

CONCLUSIONS

Our subjects were unable to alter their DTH responses using hypnotic suggestion.

Effect of sexual practices on T cell subsets and delayed hypersensitivity in transsexuals and female sex workers

To determine whether ano-receptive unprotected sexual intercourse (SI) practised by transsexuals produces immunological abnormalities we compared delayed hypersensitivity skin tests (DTH) and T cell helper (CD4) and suppressor (CD8) subsets in 57 transsexuals and 69 female sex worker controls. The populations were matched for age, duration of prostitution, number of clients and previous use of antibiotics. Heterosexual males and females and transsexuals who practised protected SI, were also included as controls. All were HIV negative. There were significantly increased absolute CD4 and CD8 counts and decreased DTH and CD4/CD8 ratios in those who practised unprotected ano-receptive SI. These changes were unlikely to be due to any of the microbial agents tested. We conclude that ano-receptive sexual intercourse results in increased immunological abnormalities in these sex workers possibly as a result of rectal exposure to seminal alloantigens. These abnormalities could play an important role as co-factors in disease transmission.

Behaviorally conditioned enhancement of delayed-type hypersensitivity in the mouse

Cyclophosphamide (CY), previously used to condition suppression of a number of different immune responses, was used to condition an enhancement of a delayed-type hypersensitivity (DTH) response in mice. Three weeks before sensitization with sheep red blood cells (SRBC), mice were conditioned by pairing their consumption of a saccharin solution (SAC) with injection of CY. Two, three, and four days after sensitization (Day 0), animals were reexposed to SAC and, on Day +3, they were injected with a low dose of CY. This dose suppressed the DTH response to a challenge with SRBC on Day +4 in both conditioned and control animals. Following rechallenge with SRBC on Days +11 and +18, however, DTH responses were enhanced. Conditioned mice that had been reexposed to SAC showed a significantly greater enhancement than either nonconditioned animals or conditioned mice that were not reexposed to SAC. Thus, enhancement as well as suppression of immune responses can be conditioned with CY.

Psychologic modulation of the human immune response to varicella zoster

Psychoimmunology, the interrelationship between the brain/mind/psyche and the immune system, is now an established area of scientific research. Based on prior investigations we hypothesized that an experienced meditator could affect her delayed hypersensitivity reaction by a psychological process. A single-case study design was employed in which the subject was skin tested weekly with varicella zoster skin test reagent. After baseline immunologic studies, she was able, as hypothesized, to significantly reduce both the induration of her delayed hypersensitivity skin test reaction and in vitro lymphocyte stimulation to varicella zoster. Then, as predicted, she was able to allow her reaction to return to baseline. As a confirmation of what is to our knowledge this previously undescribed phenomenon, she was able to reproduce the entire sequence nine months later. It appears that this subject can intentionally modulate her immune response by a psychologic mechanism.

Psychologically mediated effect on the delayed hypersensitivity reaction to tuberculin in humans

Recent research with animals has indicated a central nervous system effect on the immune system. This report describes findings of a possible psychologically mediated effect on the delayed hypersensitivity reaction to tuberculin in humans. Seven tuberculin positive subjects evidenced a decreased response to tuberculin (as measured by erythema and induration) when a paradigm similar to behavioral conditioning was followed where the subjects expected their reactions to be negative.