Effect of thymosin on T-lymphocyte rosette formation in children with kwashiorkor

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 immune system in children with malnutrition--a systematic review

BACKGROUND

Malnourished children have increased risk of dying, with most deaths caused by infectious diseases. One mechanism behind this may be impaired immune function. However, this immune deficiency of malnutrition has not previously been systematically reviewed.

OBJECTIVES

To review the scientific literature about immune function in children with malnutrition.

METHODS

A systematic literature search was done in PubMed, and additional articles identified in reference lists and by correspondence with experts in the field. The inclusion criteria were studies investigating immune parameters in children aged 1-60 months, in relation to malnutrition, defined as wasting, underweight, stunting, or oedematous malnutrition.

RESULTS

The literature search yielded 3402 articles, of which 245 met the inclusion criteria. Most were published between 1970 and 1990, and only 33 after 2003. Malnutrition is associated with impaired gut-barrier function, reduced exocrine secretion of protective substances, and low levels of plasma complement. Lymphatic tissue, particularly the thymus, undergoes atrophy, and delayed-type hypersensitivity responses are reduced. Levels of antibodies produced after vaccination are reduced in severely malnourished children, but intact in moderate malnutrition. Cytokine patterns are skewed towards a Th2-response. Other immune parameters seem intact or elevated: leukocyte and lymphocyte counts are unaffected, and levels of immunoglobulins, particularly immunoglobulin A, are high. The acute phase response appears intact, and sometimes present in the absence of clinical infection. Limitations to the studies include their observational and often cross-sectional design and frequent confounding by infections in the children studied.

CONCLUSION

The immunological alterations associated with malnutrition in children may contribute to increased mortality. However, the underlying mechanisms are still inadequately understood, as well as why different types of malnutrition are associated with different immunological alterations. Better designed prospective studies are needed, based on current understanding of immunology and with state-of-the-art methods.

Involution of thymic epithelium and low serum thymulin bioactivity in weanling mice subjected to severe food intake restriction or severe protein deficiency

The volume of epithelium in the cortex and in the medulla of the thymus was compared in four groups of weanling male and female CBA/J mice. Well-nourished controls (C), food intake restricted (R), and animals given a low-protein diet ad libitum (LP) were fed from 23 to 37 days of age. Baseline controls (B) were studied at 23 days of age. Epithelial volume fraction was estimated for each group by point-counting morphometry on electron micrographs. Other mice were used to obtain group mean estimates of thymic index (mg/g live weight) and volume fraction of cortex and medulla (light microscope-level point-counting morphometry). Cortical and medullary epithelial volumes were calculated for each animal examined by electron microscopy by obtaining the live weight and applying, in sequence, the group mean thymic index, an assumed thymic density of 1.0 mm3/mg, the group mean cortical or medullary volume fraction, and the measured cortical or medullary volume fraction for that animal. Serum thymulin bioactivity was also measured in C, R, and LP mice. The results reveal thymic epithelial involution in the two most common rodent models of malnutrition, and suggest that this may contribute to the low serum thymulin levels found in malnourished experimental animals and humans.

Thymosins and anti-thymosins: properties and clinical applications

For years, scientists have searched for ways to trigger the body's own defenses against cancer and other diseases associated with abnormal immunity. This search has led to the discovery of a number of important new biological and chemical substances that augment, direct or restore many of the normal defenses of the body. These substances are in essence the natural drugs of the body that endow us with immunity and resistance to disease. Now called biological response modifiers (BRMs), most of these 'new medicines', such as thymosins, lymphokines, and interferons, occur naturally in the body, while others, synthetic immunomodulators and thymomimetic agents (drugs that mimic thymic function) have been created in the laboratory. Previously, therapeutic drug development in this area relied upon chemical synthesis or introduction of bacterial adjuvants, or modified viral compounds and substances, which were foreign to the body. Therefore, they did not and do not rely upon or use the body's natural immune and biological response systems for protection against disease, function and response to the environment. Although scientists have known about BRMs for years, isolating and purifying them so that they could be used to treat diseases has been extremely difficult. Many of these substances, such as the lymphokines, occur in the body in minute amounts and normally do not circulate in the blood. The development of new technologies for isolation and large scale synthesis, e.g. solid phase peptide synthesis, high-pressure liquid chromatography microsequencing and genetic engineering, has now permitted scientists to isolate, purify, and synthesize BRMs in sufficiently large quantities to allow human clinical trials. In this paper we will focus on the potential clinical applications of the thymosins and anti-thymosins.

Thymosin fraction 5: effects on T cell functions in mice immunosuppressed by severe dietary protein deficiency

The present studies were performed to determine the effects of severe protein deficiency and subsequent injection of thymosin fraction 5 (TF5) on T and B cell functions. BALB/c mice, 4 weeks old, were fed a normal protein (21%), a low protein (4%) or a protein free (0%) diet and then injected with TF5 or buffer (PBS). A significant increase was observed in the PHA (phytohemagglutinin) and LPS (lipopolysaccharide) induced mitogenesis with increasing age of the well-nourished, PBS injected animals. The severely protein malnourished mice, PBS injected and the well nourished mice, injected with TF5 had smaller increases in both B and T cell mitogenesis with increasing age. TF5 injection of the malnourished mice increased PHA and LPS mitogenesis nearly to the levels of the well-nourished mice. The protein malnourished mice consistently had higher serum corticosteroid levels than controls. No changes in serum corticosteroids were observed with TF5 injection of controls, but there was a significant decrease in the corticosteroid levels of the severely malnourished with TF5 injection. Cytoxicity assays of T cell function, antibody dependent cellular cytoxicity and cytoxicity to mouse thymona tumor cells, in mice fed moderately protein deficient diets showed suppression compared to controls fed 20% protein. TF5 injection partially and temporarily increased these functions in the malnourished mice.

Cellular immune functions, endorphins, and alcohol consumption in males

The effects of alcohol abuse on cellular immune functions were measured by various levels of alcohol use in adult men. Total lifelong abstainers were used as controls. Previous abusers, current abusers, and patients with alcoholic cirrhosis or pancreatitis were age-matched to controls. T-lymphocyte mitogenesis stimulated by phytohemagglutinin and concanavalin A was generally reduced in peripheral blood lymphocytes of current and previous alcohol consumers, although the decrease was not statistically significant. B-cell mitogenesis stimulated by pokeweed mitogen was not changed by previous alcohol consumption. The number of T-cells was not changed by either previous or current alcohol abuse. T-helper cells were significantly increased and T-suppressor cells increased only in the patients with alcoholic cirrhosis or pancreatitis. The percentage of T-lymphocytes with T-suppressor characteristics in controls was 27% while in alcoholic cirrhosis or pancreatitis subjects it was 16%. Plasma corticosteroid levels were significantly increased in people currently consuming alcohol (12.1 +/- 1.1 mg/dl) compared to controls (7.7 +/- 1.1). The corticosteroid levels were also higher in previous alcohol abusers although not statistically significant. Plasma endorphin levels were increased by severe alcohol abuse in the patients with cirrhosis or pancreatitis to 25.03 +/- 6.74 from 11.85 +/- 2.48 pg/ml in controls.

Thymic peptide hormones: basic properties and clinical applications in cancer

The manuscript will provide an in-depth and critical review of the nomenclature, biochemistry, biological properties, and a summary of published and on-going clinical trials with all reported thymic preparations, including both partially purified thymic factors (e.g., thymosin fraction 5, thymostimulin) as well as purified and synthesized thymic peptides (e.g., thymosin alpha 1, thymulin). Particular emphasis will be placed on which thymic peptides should be categorized as true hormones. In addition, the comparative biochemistry and biological activity in animals will be summarized and contrasted for all the currently available thymic factors. The effects, in vitro of thymic factors, on peripheral blood lymphocytes isolated from normal donors and patients with primary immunodeficiency disorders, autoimmune disorders, and neoplastic disorders will also be reviewed. Finally, a detailed critical summary of the clinical trials performed with each of the thymic preparations will be presented with an emphasis on treatment of patients with cancer.

Immune function in the malnourished host

Deficiencies of protein, energy, and specific vitamins and minerals impair function of various components of the immunological network and therefore weaken host defense. These various deficiencies may affect specific loci within the network, but because of the interrelations between the different systems, the ultimate effect may be quite broad. Patients with PEM often suffer infections, which may also impair the immune function. It is difficult to separate effects of malnutrition from those of infection, a fact recognized in the recent coinage of the term malnutrition-infection complex. On the basis of the available information it appears that PEM and associated deficiencies of nutrients cause a major impairment in the T lymphocytes and the complement system. They have relatively less effect on the B lymphocytes and the phagocytes directly; however, normal B cell activity is dependent on regulatory influences of T cells and the phagocytic cells require mediators generated from the activation of complement. Therefore these cells also are functionally defective in PEM. The consequence of these deficiencies of function of the immune system in the malnourished host is heightened susceptibility to and a less vigorous response to infections. These defects can be generally reversed by nutritional rehabilitation.