G. A. W. Rook

Validation of housekeeping genes for normalizing RNA expression in real-time PCR.

Analysis of RNA expression using techniques like real-time PCR has traditionally used reference or housekeeping genes to control for error between samples. This practice is being questioned as it becomes increasingly clear that some housekeeping genes may vary considerably in certain biological samples. We used real-time reverse transcription PCR (RT-PCR) to assess the levels of 13 housekeeping genes expressed in peripheral blood mononuclear cell culture and whole blood from healthy individuals and those with tuberculosis. Housekeeping genes were selected from conventionally used ones and from genes reported to be invariant in human T cell culture. None of the commonly used housekeeping genes [e.g., glyceraldehyde-phosphate-dehydrogenase (GAPDH)] were found to be suitable as internal references, as they were highly variable (>30-fold maximal variability). Furthermore, genes previously found to be invariant in human T cell culture also showed large variation in RNA expression (>34-fold maximal variability). Genes that were invariant in blood were highly variable in peripheral blood mononuclear cell culture. Our data show that RNA specifying human acidic ribosomal protein was the most suitable housekeeping gene for normalizing mRNA levels in human pulmonary tuberculosis. Validations of housekeeping genes are highly specific for a particular experimental model and are a crucial component in assessing any new model.

Give us this day our daily germs

Are we sparing the dirt and spoiling our childrens immune systems? The theory that some germs are necessary in developing healthy immune systems is gaining credence as more evidence emerges. It is vital that we find out which germs are needed, when and how, before the increase in diseases attributable to faulty regulation of the immune system (allergies, autoimmunity, inflammatory bowel disease) spirals out of control.

Persistence of DNA from Mycobacterium tuberculosis in superficially normal lung tissue during latent infection

BACKGROUND A third of the worlds population has latent infection with Mycobacterium tuberculosis, and in areas of low endemicity, most cases of active tuberculosis arise as a result of reactivation of latent bacilli. We sought to establish the cellular location of these latent organisms to facilitate their elimination. METHODS We applied in-situ PCR to sections of macroscopically normal lung tissue from 13 individuals from Ethiopia and 34 from Mexico who had died from causes other than tuberculosis. Sections of lung tissue from six Norwegian individuals (ie, individuals from a non-endemic population) acted as negative controls, and six Ethiopian tuberculosis cases acted as positive controls. FINDINGS Control necropsy samples from the Norwegian individuals were all negative by in-situ PCR and conventional PCR, whereas all samples from known Ethiopian tuberculosis cases were positive by both methods. However, in macroscopically normal lung tissue from Ethiopian and Mexican individuals without tuberculous lesions, the in-situ PCR revealed five of 13 and ten of 34 positive individuals, respectively. These results were confirmed by conventional PCR with extracted DNA. Positive cells included alveolar and interstitial macrophages, type II pneumocytes, endothelial cells, and fibroblasts. INTERPRETATION M. tuberculosis can persist intracellularly in lung tissue without histological evidence of tuberculous lesions. M. tuberculosis DNA is situated not only in macrophages but also in other non-professional phagocytic cells. These findings contradict the dominant view that latent organisms exist in old classic tuberculous lesions, and have important implications for strategies aimed at the elimination of latent and persistent bacilli.

Hormones, peripherally activated prohormones and regulation of the Th1/Th2 balance

There is much interest in the factors that control the cytokine profile of T-helper (Th) lymphocytes, and attention has focused on feedback from the cytokines themselves. In general, Th1 cytokines promote Th1 activity and inhibit Th2 activity, and vice versa. Both Th1 and Th2 responses should therefore be stable. However, in vivo, many responses start predominantly as Th1 and then shift to Th2. Why do they do this? As discussed here, an important influence on this shift that has been largely ignored in in vitro work is the endocrine system.

Tryptophan metabolism in the central nervous system: medical implications

The metabolism of the amino acid L-tryptophan is a highly regulated physiological process leading to the generation of several neuroactive compounds within the central nervous system. These include the aminergic neurotransmitter serotonin (5-hydroxytryptamine, 5-HT), products of the kynurenine pathway of tryptophan metabolism (including 3-hydroxykynurenine, 3-hydroxyanthranilic acid, quinolinic acid and kynurenic acid), the neurohormone melatonin, several neuroactive kynuramine metabolites of melatonin, and the trace amine tryptamine. The integral role of central serotonergic systems in the modulation of physiology and behaviour has been well documented since the first description of serotonergic neurons in the brain some 40 years ago. However, while the significance of the peripheral kynurenine pathway of tryptophan metabolism has also been recognised for several decades, it has only recently been appreciated that the synthesis of kynurenines within the central nervous system has important consequences for physiology and behaviour. Altered kynurenine metabolism has been implicated in the pathophysiology of conditions such as acquired immunodeficiency syndrome (AIDS)-related dementia, Huntingtons disease and Alzheimers disease. In this review we discuss the molecular mechanisms involved in regulating the metabolism of tryptophan and consider the medical implications associated with dysregulation of both serotonergic and kynurenine pathways of tryptophan metabolism.

Inhibition of an established allergic response to ovalbumin in BALB/c mice by killed Mycobacterium vaccae

Allergic disorders are mediated by T lymphocytes secreting T helper 2 (Th2) cytokines, interleukin‐4 (IL‐4) and interleukin‐5 (IL‐5), resulting in high levels of serum immunoglobulin E (IgE) and recruitment of eosinophils. One of the treatment strategies is to downregulate the Th2 component by inducing a T helper 1 (Th1) response to the relevant allergen, because Th1 and Th2 cytokines are thought to be mutually antagonistic. In this study, we examined the effects of Mycobacterium vaccae, a potent inducer of Th1 immunity, on allergic responses in a murine model. A single injection of M. vaccae into ovalbumin (OVA)‐preimmunized BALB/c mice suppressed serum IgE over a wide dose range (107, 108 or 109M. vaccae). Further experiments, using 107M. vaccae injected twice, showed that this treatment inhibited not only serum IgE, but also the potential for ovalbumin‐induced IL‐5 production by spleen cells. This non‐specific ability of a mycobacterium to decrease Th2 activity, even when not presented together with the allergen, is in agreement with recent epidemiological studies on the impact of bacillus Calmette–Guérin (BCG) vaccination, and of other potent Th1 stimuli, on the incidence of atopy. The suppression of serum IgE and allergen‐specific IL‐5 synthesis by M. vaccae suggest that this organism is likely to have clinical application in the immunotherapy of allergy.

Type 2 Cytokine Gene Activation and Its Relationship to Extent of Disease in Patients with Tuberculosis

The extent of type 2 cytokine gene expression in patients with pulmonary tuberculosis (TB) was studied by use of quantitative nested reverse-transcription polymerase chain reaction on freshly isolated peripheral blood mononuclear cells. Interleukin (IL)-4 and IL-13 mRNA expression was significantly greater in patients-median mRNA copy numbers were 1.7 and 1.1 log10 higher, respectively-than in matched tuberculin-positive control subjects. Significant correlations with radiologic extent of disease and serum IgE levels supported the biologic significance of these results. Interferon-gamma mRNA copy numbers exceeded those of type 2 cytokines but were only marginally lower in patients than in control subjects. Gene expression of an IL-4 splice variant (IL-4delta2) was bimodally distributed in both patient and control groups. Patients with greater IL-4delta2 expression also expressed more IL-4 mRNA and had more extensive disease. Type 2 cytokines are associated with immunopathologic changes in TB patients but could be a cause or consequence of disease.

Review series on helminths, immune modulation and the hygiene hypothesis: The broader implications of the hygiene hypothesis

Man has moved rapidly from the hunter–gatherer environment to the living conditions of the rich industrialized countries. The hygiene hypothesis suggests that the resulting changed and reduced pattern of exposure to microorganisms has led to disordered regulation of the immune system, and hence to increases in certain inflammatory disorders. The concept began with the allergic disorders, but there are now good reasons for extending it to autoimmunity, inflammatory bowel disease, neuroinflammatory disorders, atherosclerosis, depression associated with raised inflammatory cytokines, and some cancers. This review discusses these possibilities in the context of Darwinian medicine, which uses knowledge of evolution to cast light on human diseases. The Darwinian approach enables one to correctly identify some of the organisms that are important for the ‘Hygiene’ or ‘Old Friends’ hypothesis, and to point to the potential exploitation of these organisms or their components in novel types of prophylaxis with applications in several branches of medicine.

Hygiene Hypothesis and Autoimmune Diseases

Throughout the twentieth century, there were striking increases in the incidences of many chronic inflammatory disorders in the rich developed countries. These included autoimmune disorders such as Type 1 diabetes and multiple sclerosis. Although genetics and specific triggering mechanisms such as molecular mimicry and viruses are likely to be involved, the increases have been so rapid that any explanation that omits environmental change is incomplete. This chapter suggests that a series of environmental factors, most of them microbial, have led to a decrease in the efficiency of our immunoregulatory mechanisms because we are in a state of evolved dependence on organisms with which we co-evolved (and that had to be tolerated) as inducers of immunoregulatory circuits. These organisms (“Old Friends”) are depleted from the modern urban environment. Rather than considering fetal programming by maternal microbial exposures, neonatal programming, the hygiene hypothesis, gut microbiota, and diet as separate and competing hypotheses, I attempt here to integrate these ideas under a single umbrella concept that can provide the missing immunoregulatory environmental factor that is needed to explain the recent increases in autoimmune disease.

TUMOUR NECROSIS FACTOR IN BRONCHOPULMONARY SECRETIONS OF PATIENTS WITH ADULT RESPIRATORY DISTRESS SYNDROME

Tumour necrosis factor (TNF) concentrations were measured in the bronchopulmonary secretions of 5 patients with the adult respiratory distress syndrome. Each patient underwent fibreoptic bronchoscopy and bronchopulmonary aspiration, and control samples were obtained in an identical manner from 24 patients who underwent bronchoscopy for other reasons (8 had tuberculosis, 6 had sarcoidosis, and 10 had haemoptysis but no abnormal findings). Aspirated fluid was assayed for the presence of TNF by use of an enzyme-linked immunosorbent assay. In the 5 patients with adult respiratory distress syndrome, TNF concentrations exceeded 500 U/ml (12.5 ng/ml), whereas in the control samples no TNF was detected.