Histometric studies on biopsies of tuberculin skin tests showing evidence of ischaemia and necrosis

STK3/STK4 signalling in adipocytes regulates mitophagy and energy expenditure

Obesity reduces adipocyte mitochondrial function, and expanding adipocyte oxidative capacity is an emerging strategy to improve systemic metabolism. Here, we report that serine/threonine-protein kinase 3 (STK3) and STK4 are key physiological suppressors of mitochondrial capacity in brown, beige and white adipose tissues. Levels of STK3 and STK4, kinases in the Hippo signalling pathway, are greater in white than brown adipose tissues, and levels in brown adipose tissue are suppressed by cold exposure and greatly elevated by surgical denervation. Genetic inactivation of Stk3 and Stk4 increases mitochondrial mass and function, stabilizes uncoupling protein 1 in beige adipose tissue and confers resistance to metabolic dysfunction induced by high-fat diet feeding. Mechanistically, STK3 and STK4 increase adipocyte mitophagy in part by regulating the phosphorylation and dimerization status of the mitophagy receptor BNIP3. STK3 and STK4 expression levels are elevated in human obesity, and pharmacological inhibition improves metabolic profiles in a mouse model of obesity, suggesting STK3 and STK4 as potential targets for treating obesity-related diseases.

Update on cutaneous tuberculosis

Tuberculosis continues to draw special attention from health care professionals and society in general. Cutaneous tuberculosis is an infection caused by M. tuberculosis complex, M. bovis and bacillus Calmette-Guérin. Depending on individual immunity, environmental factors and the type of inoculum, it may present varied clinical and evolutionary aspects. Patients with HIV and those using immunobiological drugs are more prone to infection, which is a great concern in centers where the disease is considered endemic. This paper aims to review the current situation of cutaneous tuberculosis in light of this new scenario, highlighting the emergence of new and more specific methods of diagnosis, and the molecular and cellular mechanisms that regulate the parasite-host interaction.

The pathogenesis and pathology of bovine tuberculosis with insights from studies of tuberculosis in humans and laboratory animal models

This paper reviews key insights the discipline of pathology has contributed to our understanding of bovine tuberculosis in the context of findings of studies of tuberculosis in humans and laboratory animal models. Analysis and extrapolation of data from other species have the potential to expand our understanding of the pathogenesis of the disease in cattle. The distribution of lesions in affected cattle, humans and laboratory animals illustrate the primacy of the respiratory tract as portal of infection and raise questions about the role of the upper respiratory tract surface, tonsil and dorsal lung regions in disease pathogenesis and transmission. The mechanisms behind significant pathological processes such as necrosis, apoptosis and liquefaction, occurring within lesions, are explored and their potential practical significance assessed in the context of herd disease dynamics and vaccine development. It is proposed that effective 'innate' host defences result in many animals and humans remaining disease-free and tuberculin test negative following exposure to infection. Furthermore, the concepts of latency and disease reactivation, considered significant factors in perpetuating tuberculosis in human populations, are explored in the context of the bovine disease.

Comparison of macro- and micro-lightguide spectrophotometric measurements of microvascular haemoglobin oxygenation in the tuberculin reaction in normal human skin

The changes in haemoglobin oxygenation (SO2) occurring in the tuberculin reaction in human skin were measured using macro- and micro-lightguide spectrophotometry and the results compared. A significant difference was found between the measurements from the respective instruments, demonstrating that the micro-lightguide technique measures only in the most superficial capillaries. Laser Doppler flux (LDF) and transcutaneous oxygen (tcpO2) measurements were also obtained concurrently. At the height of the reaction, heating did not significantly change SO2 or LDF, showing that the vessels in the skin were maximally vasodilated. Although SO2 was increased in the reaction, tcpO2 decreased. This suggests that the infiltrating cells may present a diffusion barrier to oxygen between the capillaries and the tissue cells. This study has shown that micro-lightguide spectrophotometry gives a local picture of intracapillary oxygen supply, which is useful in elucidating the pathophysiological changes occurring during chronic inflammation.

A preliminary assessment of laser Doppler perfusion imaging in human skin using the tuberculin reaction as a model

Laser Doppler imaging is a new development in the field of laser Doppler flowmetry. We were recently loaned the Lisca laser Doppler perfusion imager (LDI) manufactured by Lisca Development, Linkoping, Sweden for assessment against other methods for assessment of skin perfusion. In order to evaluate the device, it was applied to imaging flux changes induced in human skin during the tuberculin reaction. Flux values were compared directly with those from conventional lightguide laser Doppler flowmetry, and parameters measured using two other methods for assessment of tissue perfusion, dynamic thermographic imaging and tissue spectrophotometry. The results showed very good correlations between the various methods. In addition, the LDI showed that very large differences in flux values (up to 5 V) could be found within distances of only 2 mm during the tuberculin reaction and that focal centres of low flux values surrounded by higher values ('craters') could be found not only at the centre, but elsewhere in the lesion. The LDI enables rapid non-invasive detailed analysis of blood flow patterns in skin and correlates well with other methods for measuring skin perfusion. Its use to examine heterogeneity of microvascular blood flow patterns may lead to further understanding of the local mechanisms for regulation of oxygen supply to tissue.

Dynamic thermographic imaging for estimation of regional perfusion in the tuberculin reaction in healthy adults

A sensitive method for measurement of the volume of blood flow through the skin, based on the kinetics of reheating after localised cooling, is described in this paper. This method has been used to study the tuberculin reaction as a model of cutaneous delayed-type hypersensitivity (DHS) in man. Over the positive reaction there is accelerated reheating similar in kinetics and extent to that seen after maximal hyperaemia induced by intradermal injection of histamine or prostaglandin E2. The earlier phase of reheating (10-100 s) is more dependent on blood flow, whereas the later phase (100-300 s) is apparently more dependent on non-perfusion heat exchange mechanisms, including conduction. The reheat kinetic method is largely dependent on blood flow in the deep dermal vessels (diameter > 50 microns), whereas the alternative approach of measurement of the velocity of flow of erythrocytes in the microcirculation by laser Doppler (LD) flowmetry gives results biased towards the most superficial dermal circulation. Previous studies with LD flowmetry have shown that the blood velocity is greatest at the centre of weak and strong reactions, while in the most intense reactions it is raised at the centre but maximal at the periphery (central relative slowing, CRS) raising the possibility of central ischaemia. The reheat kinetics approach has now indicated that the deep dermal circulation is not impaired in CRS reactions. It is concluded that there must be partial obstruction of the parts of the microcirculation communicating between the deep and superficial dermal plexuses, presumably from the accumulation of exudate oedema in the most intense tuberculin reactions.

Early delayed hypersensitivity responses in tuberculin skin tests after heavy occupational exposure to tuberculosis

The early (six hours) reaction to tuberculin skin testing was studied in 33 Indonesian hospital workers with frequent occupational exposure to M tuberculosis and compared with responses maximal at the usual time (48 hours) in factory workers, from the same locality but with only occasional occupational exposure, to determine the nature of the early reaction. The early reaction had the same general histopathological appearance as that seen in the conventional (48 hour) reaction, and both had an infiltrate consisting largely of T lymphocytes and macrophages. The cell densities were lower in the six hour reactions, but the relative concentration of macrophages was greater in the earlier response. These histometric measurements suggested that the six hour reaction was an accelerated delayed hypersensitivity reaction. Moreover, the absence of a specific IgE response or of particulate masses of Ig or complement, made it unlikely an anaphylactoid or Arthus-type reaction could have been responsible. It is concluded that those with frequent occupational exposure to M tuberculosis have larger numbers of circulating T cells reactive with mycobacterial antigens, so that the development of the skin test response to tuberculin is less dependent on "by-stander" cell infiltration to mediate the delayed hypersensitivity reaction than the reactions in those with less intense and less frequent natural exposure. The skin test response maximal at six hours is probably a hyperimmune reaction to an antigen recognised by T cells.

Skin changes in the tuberculin test

This review describes the recent advances in knowledge of the nature and range of physiological changes that occur in the skin at the site of a positive tuberculin reaction. The infiltration of T-cells and monocyte/macrophages shows a marked compartmentalisation suggesting that the functions of particular cell types depend on their localisation. The extent of cutaneous oedema (detectable as induration) is not closely related to other features of the reaction or to systemic indicators of cell mediated immunity. The intensity of hyperaemia is maximal at the centre of the reaction and is correlated in most cases with the density of cellular infiltration in the dermis suggesting a functional coordination. Despite this correlation between cell numbers and velocity of blood flow, the reaction normally shows hypoxia, hypercapnia and local acidosis, but this metabolic modification may not be a wholly disadvantageous effect since these conditions appear to facilitate the growth and metabolism of activated lymphocytes and macrophages. In very strong reactions, there is central relative slowing of the circulation and this may lead to necrosis in extreme cases. There are however a minority of cases where cell infiltration occurs but induration is not palpable: this situation has been named pseudoanergy, and its pathogenesis has not yet been established. The occurrence of pseudoanergy must throw some doubt on the conventional criteria for positivity in the reading of tuberculin skin tests (induration greater than 5 mm) and this may have relevance to future strategies for assessment of new vaccines.(ABSTRACT TRUNCATED AT 250 WORDS)