Effects of triiodothyronine supplements on splenic natural killer cells in malnourished weanling mice

The Tolerance Model of Non-Inflammatory Immune Competence in Acute Pediatric Malnutrition: Origins, Evidence, Test of Fitness and Growth Potential

The tolerance model rests on the thesis of a physiologically regulated, albeit unsustainable, systemic attempt to adapt to the catabolic challenge posed by acute prepubescent malnutrition even in its severe forms. The model centers on the immunological component of the attempt, positing reorientation toward a non-inflammatory form of competence in place of the classic paradigm of immunological attrition and exhaustion. The foundation of the model was laid in 1990, and sixteen years later it was articulated formally on the basis of a body of evidence centered on T cell cytokines and interventions with cytokine and hormonal mediators. The benefit originally suggested was a reduced risk of autoimmune pathologies consequent to the catabolic release of self-antigens, hence the designation highlighting immune tolerance. Herein, the emergence of the tolerance model is traced from its roots in the recognition that acute malnutrition elicits an endocrine-based systemic adaptive attempt. Thereafter, the growth of the evidence base supporting the model is outlined, and its potential to shed new light on existing information is tested by application to the findings of a published clinical study of acutely malnourished children. Finally, some knowledge gaps pertinent to the model are identified and its potential for growth consonant with evolving perceptions of immunobiology is illustrated.

The Role of Thyroid Hormone in the Innate and Adaptive Immune Response during Infection

In the past decades, there has been growing evidence for a functional interaction between the thyroid hormone and the immune system. This article provides an overview of the mechanisms by which thyroid hormones affect the innate and adaptive immune response during infection. The influence of thyroid hormone on the most important players of the innate [neutrophils, macrophages, natural killer (NK) cells, and dendritic cells (DCs)] and adaptive immune system (B- and T-lymphocytes) is reviewed here based on both clinical and preclinical studies. The effects of modulation of the immune system by drugs, such as monoclonal antibodies, tyrosine kinase inhibitors, and interferons on thyroid function, are beyond the scope of this article. Thyroid hormones regulate the activity of neutrophils which is reflected by higher numbers of neutrophils outside the bloodstream and enhanced activity of the respiratory burst following stimulation with thyroid hormone. Hyperthyroidism affects neutrophil function to a larger extent than hypothyroidism. In addition to neutrophil function, macrophage function is strongly affected by thyroid hormones, with triiodothyronine having a pro-inflammatory effect in these cells. NK cell proliferation and cytotoxic activity are also dependent on thyroid hormone levels. Finally, thyroid hormones enhance DC proliferation and maturation. In the adaptive immune system, a hyperthyroid state leads to increased activation of lymphocytes. This effect of thyroid hormone is mediated by various factors including NF-κB and protein kinase C signaling pathways and the β-adrenergic receptor. In general, a hyperthyroid state leads to a more activated immune system whereas hypothyroidism leads to a less activated immune system. © 2020 American Physiological Society. Compr Physiol 10:1277-1287, 2020.

Thyroid Hormone Action on Innate Immunity

The interplay between thyroid hormone action and the immune system has been established in physiological and pathological settings. However, their connection is complex and still not completely understood. The thyroid hormones (THs), 3,3',5,5' tetraiodo-L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3) play essential roles in both the innate and adaptive immune responses. Despite much research having been carried out on this topic, the available data are sometimes difficult to interpret or even contradictory. Innate immune cells act as the first line of defense, mainly involving granulocytes and natural killer cells. In turn, antigen presenting cells, macrophages and dendritic cells capture, process and present antigens (self and foreign) to naïve T lymphocytes in secondary lymphoid tissues for the development of adaptive immunity. Here, we review the cellular and molecular mechanisms involved in T4 and T3 effects on innate immune cells. An overview of the state-of-the-art of TH transport across the target cell membrane, TH metabolism inside these cells, and the genomic and non-genomic mechanisms involved in the action of THs in the different innate immune cell subsets is included. The present knowledge of TH effects as well as the thyroid status on innate immunity helps to understand the complex adaptive responses achieved with profound implications in immunopathology, which include inflammation, cancer and autoimmunity, at the crossroads of the immune and endocrine systems.

Fidelity in Animal Modeling: Prerequisite for a Mechanistic Research Front Relevant to the Inflammatory Incompetence of Acute Pediatric Malnutrition

Inflammatory incompetence is characteristic of acute pediatric protein-energy malnutrition, but its underlying mechanisms remain obscure. Perhaps substantially because the research front lacks the driving force of a scholarly unifying hypothesis, it is adrift and research activity is declining. A body of animal-based research points to a unifying paradigm, the Tolerance Model, with some potential to offer coherence and a mechanistic impetus to the field. However, reasonable skepticism prevails regarding the relevance of animal models of acute pediatric malnutrition; consequently, the fundamental contributions of the animal-based component of this research front are largely overlooked. Design-related modifications to improve the relevance of animal modeling in this research front include, most notably, prioritizing essential features of pediatric malnutrition pathology rather than dietary minutiae specific to infants and children, selecting windows of experimental animal development that correspond to targeted stages of pediatric immunological ontogeny, and controlling for ontogeny-related confounders. In addition, important opportunities are presented by newer tools including the immunologically humanized mouse and outbred stocks exhibiting a magnitude of genetic heterogeneity comparable to that of human populations. Sound animal modeling is within our grasp to stimulate and support a mechanistic research front relevant to the immunological problems that accompany acute pediatric malnutrition.

Feeding the immune system

A well-functioning immune system is key to providing good defence against pathogenic organisms and to providing tolerance to non-threatening organisms, to food components and to self. The immune system works by providing an exclusion barrier, by identifying and eliminating pathogens and by identifying and tolerating non-threatening sources of antigens, and by maintaining a memory of immunological encounters. The immune system is complex involving many different cell types distributed throughout the body and many different chemical mediators some of which are involved directly in defence while others have a regulatory role. Babies are born with an immature immune system that fully develops in the first few years of life. Immune competence can decline with ageing. The sub-optimal immune competence that occurs early and late in life increases susceptibility to infection. Undernutrition decreases immune defences, making an individual more susceptible to infection. However, the immune response to an infection can itself impair nutritional status and alter body composition. Practically all forms of immunity are affected by protein-energy malnutrition, but non-specific defences and cell-mediated immunity are most severely affected. Micronutrient deficiencies impair immune function. Here, vitamins A, D and E, and Zn, Fe and Se are discussed. The gut-associated lymphoid tissue is especially important in health and well-being because of its close proximity to a large and diverse population of organisms in the gastrointestinal tract and its exposure to food constituents. Certain probiotic bacteria which modify the gut microbiota enhance immune function in laboratory animals and may do so in human subjects.

Thyroid hormones as modulators of immune activities at the cellular level

BACKGROUND

Increasing evidence suggests that thyroid hormones, L-thyroxine (T(4)) and 3,3',5-triiodo-L-thyronine (T(3)), are modulators of the immune response. In monocytes, macrophages, leukocytes, natural killer cells, and lymphocytes, a wide range of immune functions such as chemotaxis, phagocytosis, generation of reactive oxygen species (ROS), and cytokine synthesis and release are altered under hypo- and hyperthyroid conditions.

SUMMARY

Hyperthyroidism decreases the proinflammatory activities of monocytes and macrophages, whereas enhancement of phagocytosis and increased levels of ROS may occur during hypothyroidism. The expression of proinflammatory molecules such as macrophage inflammatory protein-1α and interleukin-1β increases in hypothyroidism. However, in Kupffer cells, proinflammatory activities such as the respiratory burst, nitric oxide synthase activity, and tumor necrosis factor-α expression may result from increased T(3) levels. Thyroid hormones also affect natural killer cell activity and cell-mediated immune responses. Still, for many immune cells no clear correlation has been found so far between abnormally high or low T(3) or T(4) levels and the effects observed on the immune responses.

CONCLUSIONS

In this review we outline the contributions of thyroid hormones to different aspects of innate and adaptive immune responses. The relationship between thyroid hormones and immune cells is complex and T(3) and T(4) may modulate immune responses through both genomic and nongenomic mechanisms. Future studies of the molecular signaling mechanisms involved in this cross-talk between thyroid hormones and the immune system may support development of new strategies to improve clinical immune responses.

Possible stimulation of anti-tumor immunity using repeated cold stress: a hypothesis

Background

The phenomenon of hormesis, whereby small amounts of seemingly harmful or stressful agents can be beneficial for the health and lifespan of laboratory animals has been reported in literature. In particular, there is accumulating evidence that daily brief cold stress can increase both numbers and activity of peripheral cytotoxic T lymphocytes and natural killer cells, the major effectors of adaptive and innate tumor immunity, respectively. This type of regimen (for 8 days) has been shown to improve survival of mice infected with intracellular parasite Toxoplasma gondii, which would also be consistent with enhanced cell-mediated immunity.

Presentation of the hypothesis

This paper hypothesizes that brief cold-water stress repeated daily over many months could enhance anti-tumor immunity and improve survival rate of a non-lymphoid cancer. The possible mechanism of the non-specific stimulation of cellular immunity by repeated cold stress appears to involve transient activation of the sympathetic nervous system, hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes, as described in more detail in the text. Daily moderate cold hydrotherapy is known to reduce pain and does not appear to have noticeable adverse effects on normal test subjects, although some studies have shown that it can cause transient arrhythmias in patients with heart problems and can also inhibit humoral immunity. Sudden immersion in ice-cold water can cause transient pulmonary edema and increase permeability of the blood-brain barrier, thereby increasing mortality of neurovirulent infections.

Testing the hypothesis

The proposed procedure is an adapted cold swim (5–7 minutes at 20 degrees Celsius, includes gradual adaptation) to be tested on a mouse tumor model. Mortality, tumor size, and measurements of cellular immunity (numbers and activity of peripheral CD8+ T lymphocytes and natural killer cells) of the cold-exposed group would be compared to those of control groups (warm swim and no treatment). Cold-water stress would be administered twice a day for the duration of several months.

Implications of the hypothesis

If the hypothesis is supported by empirical studies and the method is shown to be safe, this could lead to the development of an adjunctive immunotherapy for some (non-lymphoid) cancers, including those caused by viral infections.

Re-feeding rapidly restores protection againstHeligmosomoides bakeri(Nematoda) in protein-deficient mice

This study determined whether the timing of re-feeding of protein-deficient mice restored functional protection against the gastrointestinal nematode,Heligmosomoides bakeri. Balb/c mice were fed a 3% protein-deficient (PD) diet and then transferred to 24% protein-sufficient (PS) diet either on the day of primary infection, 10 days after the primary infection, on the day of challenge infection, or 7 days after the challenge infection. Control mice were fed either the PD or PS diet. Onset of challenge, but not primary, infection caused short-term body weight loss, anorexia and reduced feed efficiency. Weight gain was delayed in mice when re-feeding commenced on the day of challenge infection; alkaline phosphatase (ALP) was also elevated in these mice on day 28 post-challenge. In contrast, other re-feeding groups attained similar body weights to PS mice within 4 days and had similar ALP at day 28. Serum leptin was higher in PD than PS mice and positively associated with food intake. As expected, worm survival was prolonged in mice fed the PD diet. However, egg production and worm burdens were similar in all re-feeding groups to the PS mice, indicating that protein re-feeding during either the primary or challenge infection rapidly restored normal parasite clearance.

Tumoricidal activity of lymphokine-activated killer cells during acute protein restriction in the cotton rat (Sigmodon hispidus)

Habitat-induced alterations of immune system function have been implicated in the regulation of survival rates in wild herbivore populations. Protein availability in the diet has been shown to fluctuate with density and influence immunity in hispid cotton rats (Sigmodon hispidus), a common herbivorous rodent of the southeastern United States. In this study, we examined the impact of short-term, moderate restrictions in dietary protein on the tumoricidal activity of lymphokine-activated killer (LAK) cells in the spleen of subadult male cotton rats in captivity. Animals were fed complete, isocaloric diets containing either 20% casein (high quality diet), or one of three moderate levels of protein (10, 8, or 5% casein) for two weeks prior to assessing LAK cell activity in vitro in the presence of YAC-1 tumor cells. Moderate restrictions in protein resulted in depressed body growth, although all animals gained mass during the second week of the trial, without significant increases in food intake. Immune organ development and cellularity were suppressed in moderately restricted cotton rats when compared to those on a high quality diet. Tumoricidal activity of LAK cells against YAC-1 targets were significantly altered by diet treatments, being elevated in the group fed a diet containing 10% casein. There was a general tendency for increased LAK cell activity among those fed one of the three moderate quality diets, but observed suppressions in splenic cellularity tended to result in a slight decline in total lytic capacity of spleens.