Natural killer cell function and psychological distress in women with and without irritable bowel syndrome

Current insights into the innate immune system dysfunction in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional bowel disorder associated with abdominal pain and alterations in bowel habits. The presence of IBS greatly impairs patients' quality of life and imposes a high economic burden on the community; thus, there is intense pressure to reveal its elusive pathogenesis. Many etiological mechanisms have been implicated, but the pathophysiology of the syndrome remains unclear. As a result, novel drug development has been slow and no pharmacological intervention is universally accepted. A growing evidence implicates the role of low-grade inflammation and innate immune system dysfunction, although contradictory results have frequently been presented. Mast cells (MC), eosinophils and other key immune cells together with their mediators seem to play an important role, at least in subgroups of IBS patients. Cytokine imbalance in the systematic circulation and in the intestinal mucosa may also characterize IBS presentation. Toll-like receptors and their emerging role in pathogen recognition have also been highlighted recently, as dysregulation has been reported to occur in patients with IBS. This review summarizes the current knowledge regarding the involvement of any immunological alteration in the development of IBS. There is substantial evidence to support innate immune system dysfunction in several IBS phenotypes, but additional studies are required to better clarify the underlying pathogenetic pathways. IBS heterogeneity could potentially be attributed to multiple causes that lead to different disease phenotypes, thus explaining the variability found between study results.

Rare Variants of the Serotonin Transporter Are Associated With Psychiatric Comorbidity in Irritable Bowel Syndrome

Alterations in serotonin signaling are suspected in the pathophysiology of irritable bowel syndrome (IBS). By modulating the extracellular reuptake of serotonin, the serotonin transporter (SERT) acts as a key regulator of the bioavailability of serotonin. This study is the first to investigate the impact of rare SERT variants (i.e., those with a minor allele frequency of < 1%) on the risk for IBS, gastrointestinal (GI) symptom level, response to cognitive-behavioral treatment, and psychiatric comorbidity. We sequenced a 0.19 megabase chromosomal stretch containing the SERT gene and surrounding regions in a community sample of 304 IBS patients and 83 controls. We found no significant associations between rare variants in and around the SERT gene and IBS risk, GI symptom profile, or response to treatment. We found preliminary evidence, however, that IBS subjects with a history of either depression or anxiety were significantly more likely to carry multiple rare likely functional variant alleles than IBS patients without psychiatric comorbidity.

What does irritable bowel syndrome share with non-alcoholic fatty liver disease?

Non-alcoholic fatty liver disease (NAFLD) and irritable bowel syndrome (IBS) are two very common diseases in the general population. To date, there are no studies that highlight a direct link between NAFLD and IBS, but some recent reports have found an interesting correlation between obesity and IBS. A systematic PubMed database search was conducted highlighting that common mechanisms are involved in many of the local and systemic manifestations of NAFLD, leading to an increased cardiovascular risk, and IBS, leading to microbial dysbiosis, impaired intestinal barrier and altered intestinal motility. It is not known when considering local and systemic inflammation/immune system activation, which one has greater importance in NAFLD and IBS pathogenesis. Also, the nervous system is implicated. In fact, inflammation participates in the development of mood disorders, such as anxiety and depression, characteristics of obesity and consequently of NAFLD and, on the other hand, in intestinal hypersensitivity and dysmotility.

TPH gene polymorphisms are associated with disease perception and quality of life in women with irritable bowel syndrome

The aims of this exploratory study were to examine whether tryptophan hydroxylase (TPH) gene polymorphisms are associated with psychosocial factors in women with irritable bowel syndrome (IBS). TPH is the rate-limiting enzyme in the biosynthesis of serotonin and has two isoforms, TPH1 and TPH2. Four single nucleotide polymorphisms (SNPs) in the TPH1 gene and one SNP in the TPH2 gene were selected based on previous studies investigating associations between these SNPs and psychiatric or behavioral disorders. One hundred ninety-nine Caucasian women with IBS were included. Results of univariate analysis showed no association between TPH1and TPH2 gene SNPs and current level of psychological distress or psychiatric illness. However, TPH1 gene SNPs were associated with IBS-related cognitions (rs4537731 and rs21105) and quality of life (rs684302 and rs1800532), in particular the mental health and energy subscales. These associations were independent of the subjects' levels of gastrointestinal symptoms. These results suggest that patients' perception of their illness, and of the impact it has on their lives, may be subject to genetic influences, in this case sequence variants in TPH1. However, caution should be used in interpreting these results given the large number of hypothesis tests performed in this exploratory hypothesis-generating study, and the results should be considered tentative until confirmed in an independent sample.

Immunophenotyping in post-giardiasis functional gastrointestinal disease and chronic fatigue syndrome

Background

A Giardia outbreak was associated with development of post-infectious functional gastrointestinal disorders (PI-FGID) and chronic fatigue syndrome (PI-CFS). Markers of immune dysfunction have given conflicting results in CFS and FGID patient populations. The aim of this study was to evaluate a wide selection of markers of immune dysfunction in these two co-occurring post-infectious syndromes.

Methods

48 patients, reporting chronic fatigue in a questionnaire study, were clinically evaluated five years after the outbreak and grouped according to Fukuda criteria for CFS (n=19) and idiopathic chronic fatigue (n=5) and Rome II criteria for FGIDs (n=54). 22 Giardia exposed non-fatigued individuals and 10 healthy unexposed individuals were recruited as controls. Peripheral blood lymphocyte subsets were analyzed by flow cytometry.

Results

In peripheral blood we found significantly higher CD8 T-cell levels in PI-FGID, and significantly lower NK-cell levels in PI-CFS patients. Severity of abdominal and fatigue symptoms correlated negatively with NK-cell levels. A tendency towards lower T-cell CD26 expression in FGID was seen.

Conclusion

Patients with PI-CFS and/or PI-FGID 5 years after Giardia lamblia infection showed alterations in NK-cell and CD8-cell populations suggesting a possible immunological abnormality in these conditions. We found no significant changes in other markers examined in this well-defined group of PI-CFS and PI-FGID elicited by a gastrointestinal infection. Controlling for co-morbid conditions is important in evaluation of CFS-biomarkers.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Neural and neuro-immune mechanisms of visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized as functional because a pathobiological cause is not readily apparent. Considerable evidence, however, documents that sensitizing proinflammatory and lipotoxic lipids, mast cells and their products, tryptases, enteroendocrine cells, and mononuclear phagocytes and their receptors are increased in tissues of IBS patients with colorectal hypersensitivity. It is also clear from recordings in animals of the colorectal afferent innervation that afferents exhibit long-term changes in models of persistent colorectal hypersensitivity. Such changes in afferent excitability and responses to mechanical stimuli are consistent with relief of discomfort and pain in IBS patients, including relief of referred abdominal hypersensitivity, upon intra-rectal instillation of local anesthetic. In the aggregate, these experimental outcomes establish the importance of afferent drive in IBS, consistent with a larger literature with respect to other chronic conditions in which pain is a principal complaint (e.g., neuropathic pain, painful bladder syndrome, fibromyalgia). Accordingly, colorectal afferents and the environment in which these receptive endings reside constitute the focus of this review. That environment includes understudied and incompletely understood contributions from immune-competent cells resident in and recruited into the colorectum. We close this review by highlighting deficiencies in existing knowledge and identifying several areas for further investigation, resolution of which we anticipate would significantly advance our understanding of neural and neuro-immune contributions to IBS pain and hypersensitivity.

Associations of tryptophan hydroxylase gene polymorphisms with irritable bowel syndrome

BACKGROUND

Alterations in serotonin (5-HT) are suspected in the pathophysiology of irritable bowel syndrome (IBS). Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin and has two isoforms: TPH1 and TPH2. Genetic variants in both genes have been studied in various disorders related to serotonin dysregulation. The aim of this study was to examine whether TPH gene variants were associated with IBS and IBS-related gastrointestinal (GI) symptoms.

METHODS

Five single nucleotide polymorphisms (SNPs) from the TPH1 and one SNP from the TPH2 were genotyped in 199 IBS patients and 79 healthy controls. All subjects were Caucasian women of European origin. Irritable bowel syndrome patients filled in a daily diary with five GI symptoms and stool characteristics for 28 days.

KEY RESULTS

The TPH1 SNPs showed no association with the diagnosis of IBS. However, among IBS patients, all five TPH1 SNPs showed some association with diarrhea and loose type of stool consistency, with P-values rating from 0.01 to 0.20. The TPH2 SNP showed a trend towards a reduced risk of IBS and possible associations with stool characteristics, both hard and loose stools. However, no P-values were less than the conservative multiple-comparison-adjusted threshold of 0.001 and hence these results must be interpreted cautiously.

CONCLUSIONS & INFERENCES

This study is the first to assess associations of TPH gene variants with IBS-related GI symptoms and stool characteristics. The possible association of TPH gene variants with diarrhea needs to be verified in an independent sample.

Asking the why questions: a career in science

This paper describes the career path of one woman scientist and identifies the factors that promote a productive and rewarding career. Factors include a strong personal interest in the area of study, mentorship at all stages of development, collaborative relationships with colleagues in and beyond one's discipline, and family and social support. A career focused on understanding the role of stress in gastrointestinal distress is described.

Immune function and health outcomes in women with depression

This research reports immune function and health outcomes in women with depression, as compared with a non-depressed control group. Using Psychoneuroimmunolgy theory and a descriptive comparison design, scores on the Beck Depression Inventory (BDI) were used to divide 40 non-hospitalized Caucasian women between the ages of 18 and 65 years into either the control or depression comparison group. Women with depression were found to report significantly more incidences of illness over the previous two months and they were found to have significantly more indicators of illness at the time of the exam as compared to the controls. However, contrary to what has been documented in some earlier studies of depression, women with depression were not found to have significantly different immune function measures as compared to the control group. There was also no significant correlation between scores on the BDI and natural killer cell cytotoxicity in this study. While these findings support a connection between depression and both increased self-report of illness and increased signs and symptoms of minor illness or inflammation on physical exam, this study was not able to document that these effects were related to decreased immune function, as measured by natural killer cell activity or white blood cell counts.

Pathogenesis of IBS: role of inflammation, immunity and neuroimmune interactions

IBS is one of the most common functional gastrointestinal disorders worldwide and is thought to be the result of disturbed neural function along the brain-gut axis. The mechanisms behind this disturbance are not clear, but important roles for low-grade inflammation and immunological alterations in the development of symptoms compatible with IBS have become evident. The development of long-standing gastrointestinal symptoms after infectious gastroenteritis and patients with IBD in remission frequently having functional gastrointestinal symptoms support this hypothesis. An increased innate immune activity in the intestinal mucosa and in blood is found in subpopulations of patients with IBS. Mast cells and monocytes seem to be particularly important. In addition, studies have demonstrated that IBS may be associated with an activated adaptive immune response. Increased epithelial barrier permeability and an abnormal gut flora might lead to increased activation of the intestinal immune system. Functional and anatomical evidence for abnormal neuroimmune interactions has been found in patients with IBS. The link between immune alterations and severity of gastrointestinal symptoms and the positive effect of anti-inflammatory treatments in IBS further highlight the relevance of neuroimmune interactions in this condition.

Innate immune markers in mothers and fathers of children newly diagnosed with cancer

OBJECTIVE

The diagnosis of a life-threatening illness in a child is one of the most stressful events imaginable for parents and is associated with increased anxiety and distress. Despite associations between stress and immune function in animal and human models, the immune function in caregivers of children at the time of a child-related potentially traumatic event, like cancer, is not known.

METHODS

Nineteen parents (11 mothers, 8 fathers), representing six caregiver pairs, provided blood for natural killer (NK) cell count by flow cytometry and function assays [% NK whole blood, absolute NK whole blood, LU(20) (lytic unit) peripheral blood mononuclear cells, LU(20) NK cells] and completed self-report measures (acute stress) within 2 weeks of learning their child had cancer. The NK cell assay was also completed with a sample of healthy adults, the immune reference group.

RESULTS

There were similar levels of NK cell activity between caregivers and the immune reference group. Immune level and psychological outcomes were not associated. LU(20) peripheral blood mononuclear cells and LU(20) NK cells were each correlated at r = 0.83 between mothers and fathers in the same family.

CONCLUSIONS

Although based on a small sample, these preliminary results suggest that knowledge about stress responses in parents of children with life-threatening illness may be important and provide novel data regarding the shared impact of stress on immune function within caregiver dyads.

Psychoneuroimmunology and occupational therapy for inflammatory disorders

The occupational therapy profession was founded in 1917 on the notion that occupations contribute to psychological well being and physical adaptation. The credibility of occupational therapy has been threatened because the scientific basis of this notion is not always evident. The focus of occupational therapy in many physical settings has therefore shifted away from its original ethos towards one of physical problem solving and discharge facilitation.

Psychoneuroimmunology (PNI) is a developing branch of science that provides a theoretical framework to support the profession’s return to its original ethos of using occupations to promote health. This paper is an analysis of psychoneuroimmunological evidence to support occupational therapy for inflammatory disorders. A broad literature search revealed mind-body inflammatory pathways including anatomical links, nerve growth factor, adrenocorticotrophin, cortisol, somatostatin and substance-P.

Public speaking stress-induced neuroendocrine responses and circulating immune cell redistribution in irritable bowel syndrome

OBJECTIVES

Augmented neuroendocrine stress responses and altered immune functions may play a role in the manifestation of functional gastrointestinal (GI) disorders. We tested the hypothesis that IBS patients would demonstrate enhanced psychological and endocrine responses, as well as altered stress-induced redistribution of circulating leukocytes and lymphocytes, in response to an acute psychosocial stressor when compared with healthy controls.

METHODS

Responses to public speaking stress were analyzed in N = 17 IBS patients without concurrent psychiatric conditions and N = 12 healthy controls. At baseline, immediately following public speaking, and after a recovery period, state anxiety, acute GI symptoms, cardiovascular responses, serum cortisol and plasma adrenocorticotropic hormone (ACTH) were measured, and numbers of circulating leukocytes and lymphocyte subpopulations were analyzed by flow cytometry.

RESULTS

Public speaking led to significant cardiovascular activation, a significant increase in ACTH, and a redistribution of circulating leukocytes and lymphocyte subpopulations, including significant increases in natural killer cells and cytotoxic/suppressor T cells. IBS patients demonstrated significantly greater state anxiety both at baseline and following public speaking. However, cardiovascular and endocrine responses, as well as the redistribution of circulating leukocytes and lymphocyte subpopulations after public speaking stress, did not differ for IBS patients compared with controls.

CONCLUSIONS

In IBS patients without psychiatric comorbidity, the endocrine response as well as the circulation pattern of leukocyte subpopulations to acute psychosocial stress do not differ from healthy controls in spite of enhanced emotional responses. Future studies should discern the role of psychopathology in psychological and biological stress responses in IBS.

Abdominal pain impacts quality of life in women with irritable bowel syndrome

OBJECTIVES

Patients with irritable bowel syndrome (IBS) report lower health-related quality of life (QoL) as compared to healthy controls. The aims of this analysis were to describe which IBS symptoms were rated on a daily diary as most distressing/severe by IBS women, and determine which IBS symptoms were most predictive of lower QoL and have the greatest impact on daily life.

METHODS

This report is a secondary analysis of prospective and retrospective symptom severity and impact data, collected on 242 women with IBS, aged 18-48, who were studied between 1997 and 2004.

RESULTS

On the daily diary, intestinal gas was the most frequent IBS symptom with subjects reporting at least minimal intestinal gas on 74% of days and moderate or worse severity on 27% of days. Abdominal pain occurred at least minimally on 62% of days. Diarrhea was the least common. Across women, abdominal pain was most strongly related to life impact variables and QoL, followed by intestinal gas and bloating. Analysis of day-to-day variation within women showed that abdominal pain was most strongly correlated with daily life impact variables and constipation had the weakest correlation. While diarrhea had a lower correlation with life impact, this was due to the low prevalence of diarrhea. When it occurs, diarrhea has a large impact. Partial correlation analysis showed that the impact of diarrhea is independent of abdominal pain.

CONCLUSION

Abdominal pain is the most disruptive IBS symptom. Diarrhea also has an independent and significant impact when it occurs, especially in those with diarrhea-predominant IBS.

Pain, psychological variables, sleep quality, and natural killer cell activity in midlife women with and without fibromyalgia

In women with fibromyalgia (FM), central nervous system (CNS) dysfunction in pain, mood, and sleep processes could be associated with changes in immune system indicators. The primary purpose of this study was to compare pain, psychological variables, subjective and objective sleep quality, lymphocyte phenotypes and activation markers, and natural killer activity (NKA) in midlife women with and without FM. A secondary purpose was to explore relationships among these variables in a step-wise regression. Subjects had pain pressure tender points assessed, completed a psychiatric interview and questionnaires (Beck Depression Inventory, SCL-90, Profile of Mood States, subjective sleep), and underwent polysomnograhic assessment for two consecutive nights. Lymphocyte phenotypes, activation markers, and NKA were assessed from blood drawn the morning after sleep laboratory night 2. Compared to controls, women with FM had lower pain thresholds, more psychological distress, higher depression scores, and reduced subjective and objective sleep quality. They also had fewer NK cells (p <.009) and more NK cells that expressed the IL-2 receptor (p <.04), but these differences were not statistically significant after correction for multiple comparisons. NKA was not statistically significantly lower in the women with FM compared to controls. In a multiple regression of age, tender point threshold, depression, psychological distress, and sleep efficiency, only the effect of group was significant (F = 5.479, p <.03) on NKA. In conclusion, we found little evidence to support the hypothesis that pain, mood, and sleep symptoms are associated with changes in the enumeration of peripheral lymphocytes or function in FM.

Stress, stress response, and health

Components of stress and the stress response differ between men and women. The tend-and-befriend response, mediated by oxytocin and endogenous opioids, may be more applicable to women than the fight-or-flight response, which was based largely on studies of men. Even within the flight-or-flight response pattern there are sex-based differences. The HPA axis interacts with reproductive function, such as menstruation. For immune function there are sex differences as well as differences within the menstrual phase. Inclusion of men and women in stress response studies is critical. Further study is needed to clarify the influence of ovarian hormones on the stress and immune responses during the reproductive stages in women's lives, including menarche. pregnancy, and perimenopause.

Natural killer cell cytotoxicity: a methods analysis of 51chromium release versus flow cytometry

The purpose of this study is to describe design considerations for the use of flow cytometry (FC) compared to 51chromium (51Cr)-release assays utilizing cryopreserved peripheral blood mononuclear cells (PBMCs) to detect natural killer (NK) cell cytotoxicity. Subjects were 10 healthy women aged 18 to 39 years. Intra-assay variability between methods differed only at the lowest effector-target ratios evaluated. Interassay variability was wide but did not differ between methods. The relationship of lytic unit-10 between methods was strongly positive. Cytotoxicity detected by 51Cr release was higher than that detected by FC for all 10 subjects. Cost was comparable. However, had more assays been performed, technician time would have been greater with flow cytometry. More whole blood was needed to perform the flow cytometry cytotoxicity assay than 51Cr-release cytotoxicity assay. The authors found no compelling reason to adopt NK cell cytotoxicity by flow cytometry over 51Cr release.

Sense of coherence and quality of life in women with and without irritable bowel syndrome

BACKGROUND

Despite ongoing physical and psychological distress, little is known about sense of coherence (SOC) and holistic quality of life (QOL) in women with irritable bowel syndrome (IBS).

OBJECTIVES

The purposes of this study were to (a) describe and compare SOC and holistic QOL of women with and without IBS, and (b) examine the relationships among SOC, holistic QOL, and gastrointestinal (GI) and psychological distress symptoms.

METHOD

A two-group comparison design was used to test the study hypotheses that women with IBS would have lower SOC and holistic QOL than control women without IBS, and that SOC and holistic QOL would be inversely related to GI and psychological distress. A total of 324 women were studied (n= 235 with IBS, n= 89 controls). Measures included the 13-item SOC Questionnaire, Modified Flanagan QOL Scale, Bowel Disease Questionnaire, and Symptom-Checklist-90-R.

RESULTS

Both SOC and holistic QOL were lower in women with IBS (p <.001). Correlations between SOC and global distress, depression, anxiety, and somatization without GI symptoms were moderately and inversely related (r= -.64, -.64, -.53, and -.31, respectively; p <.001) in the total sample. Relationships between holistic QOL and psychological distress indicators were universally of lower magnitude (r= -.56 to -.27, p <.001). The only GI symptom indicator significantly related to SOC and holistic QOL was alternating constipation and diarrhea (tau= -.21 and -.17, respectively; p <.001).

DISCUSSION

Women with IBS have a reduced SOC and holistic QOL when compared to women without IBS. It remains to be determined whether interventions targeted at enhancing SOC and holistic QOL can impact the psychological distress associated with IBS.