Bioassay determinations of thymopoietin and thymic hormone levels in human plasma

Cell Senescence and Central Regulators of Immune Response

Pathways regulating cell senescence and cell cycle underlie many processes associated with ageing and age-related pathologies, and they also mediate cellular responses to exposure to stressors. Meanwhile, there are central mechanisms of the regulation of stress responses that induce/enhance or weaken the response of the whole organism, such as hormones of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic and parasympathetic systems, thymic hormones, and the pineal hormone melatonin. Although there are many analyses considering relationships between the HPA axis and organism ageing, we found no systematic analyses of relationships between the neuroendocrine regulators of stress and inflammation and intracellular mechanisms controlling cell cycle, senescence, and apoptosis. Here, we provide a review of the effects of neuroendocrine regulators on these mechanisms. Our analysis allowed us to postulate a multilevel system of central regulators involving neurotransmitters, glucocorticoids, melatonin, and the thymic hormones. This system finely regulates the cell cycle and metabolic/catabolic processes depending on the level of systemic stress, stage of stress response, and energy capabilities of the body, shifting the balance between cell cycle progression, cell cycle stopping, senescence, and apoptosis. These processes and levels of regulation should be considered when studying the mechanisms of ageing and the proliferation on the level of the whole organism.

Precursors of thymic peptides as stress sensors

INTRODUCTION

A large volume of data indicates that the known thymic hormones, thymulin, thymopoietin, thymosin-α, thymosin-β, and thymic humoral factor-y2, exhibit different spectra of activities. Although large in volume, available data are rather fragmented, resulting in a lack of understanding of the role played by thymic hormones in immune homeostasis.

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Existing data compartmentalizes the effect of thymic peptides into 2 categories: influence on immune cells and interconnection with neuroendocrine systems. The current study draws attention to a third aspect of the thymic peptide effect that has not been clarified yet, wherein ubiquitous and highly abundant intranuclear precursors of so called 'thymic peptides' play a fundamental role in all somatic cells.

EXPERT OPINION

Our analysis indicated that, under certain stress-related conditions, these precursors are cleaved to form immunologically active peptides that rapidly leave the nucleus and intracellular spaces, to send 'distress signals' to the immune system, thereby acting as stress sensors. We propose that these peptides may form a link between somatic cells and immune as well as neuroendocrine systems. This model may provide a better understanding of the mechanisms underlying immune homeostasis, leading thereby to the development of new therapeutic regimes utilizing the characteristics of thymic peptides.

Extracellular Ubiquitin is the Causal Link between Stored Blood Transfusion Therapy and Tumor Progression in a Melanoma Mouse Model

Background: The transfusion of blood that has been stored for some time was found to be associated with transfusion-related immune modulation (TRIM) responses in cancer patients, which could result in poor clinical outcomes, such as tumor recurrence, metastasis and reduced survival rate. Given the prior observation of the positive correlation between ubiquitin content in whole blood and storage duration by the investigators of the present study, it was hypothesized that this could be the causal link behind the association between the transfusion of stored blood and poor cancer prognosis.

Methods: In the present study, a melanoma mouse model was used to study the potential clinical impact of ubiquitin present in stored blood on cancer prognosis through a variety of cell biology methods, such as flow cytometry and immunohistochemistry.

Results: Both extracellular ubiquitin and the infusion of stored mice blood that comprised of ubiquitin reduced the apoptotic rate of melanoma cells, promoted lung tumor metastasis and tumor progression, and reduced the long-term survival rate of melanoma mice. In addition, the upregulation of tumor markers and tumorigenic TH2 cytokine generation, as well as reduced immune cell numbers, were observed in the presence of ubiquitin.

Conclusions: The present findings provide novel insights into the role of ubiquitin in immune regulation in a melanoma mouse model, and suggest ubiquitin as the causal link between allogeneic blood transfusion therapy and poor cancer prognosis.

Extracellular ubiquitin: immune modulator and endogenous opponent of damage-associated molecular pattern molecules

Ubiquitin is a post-translational protein modifier and plays essential roles in all aspects of biology. Although the discovery of ubiquitin introduced this highly conserved protein as a molecule with extracellular actions, the identification of ubiquitin as the ATP-dependent proteolysis factor 1 has focused subsequent research on its important intracellular functions. Little attention has since been paid to its role outside of the cell. During recent years, multiple observations suggest that extracellular ubiquitin can modulate immune responses and that exogenous ubiquitin has therapeutic potential to attenuate exuberant inflammation and organ injury. These observations have not been integrated into a comprehensive assessment of its possible role as an endogenous immune modulator. This review recapitulates the current knowledge about extracellular ubiquitin and discusses an emerging facet of its role in biology during infectious and noninfectious inflammation. The synopsis of these data along with the recent identification of ubiquitin as a CXCR4 agonist suggest that extracellular ubiquitin may have pleiotropic roles in the immune system and functions as an endogenous opponent of DAMPs. Functions of extracellular ubiquitin could constitute an evolutionary conserved control mechanism aimed to balance the immune response and prevent exuberant inflammation. Further characterization of its mechanism of action and cellular signaling pathways is expected to provide novel insights into the regulation of the innate immune response and opportunities for therapeutic interventions.

Solid-phase peptide synthesis and biological activity of bovine thymopoietin II (bTP-II)

Bovine thymopoietin (bTP), a 49 amino acid polypeptide, was synthesized using Merrifield's solid-phase peptide synthesis methodology. The polypeptide was purified using anion-exchange chromatography and reversed-phase HPLC and characterized by mass spectrometry and amino acid analysis of the full-length peptide and of products derived from digestion with Staphylococcus aureus V8 protease. The biological activity of the synthesized product was tested in several assay systems. Synthetic bTP was found to induce the expression of Thy 1.2 antigen on T-lymphocytes from athymic mice, in agreement with previous studies on the biological activity of endogenous bTP. Biological activity at skeletal muscle and neuronal nicotinic acetylcholine receptor sites, as reported by others for bTP, could not be confirmed in our studies. The absence of biological activity at nicotinic receptor sites may be related to the results of a recent report demonstrating the presence of a cobratoxin-like molecule in preparations of natural bTP. These data indicate that synthetic peptides have an important role for the evaluation of the specificity of the biological activity of polypeptides.

Thymopoietin, a thymic polypeptide, potently interacts at muscle and neuronal nicotinic alpha-bungarotoxin receptors

Current studies suggest that several distinct populations of nicotinic acetylcholine (ACh) receptors exist. One of these is the muscle-type nicotinic receptors with which neuromuscular nicotinic receptor ligands and the snake toxin alpha-bungarotoxin interact. alpha-Bungarotoxin potently binds to these nicotinic receptors and blocks their function, two characteristics that have made the alpha-toxin a very useful probe for the characterization of these sites. In neuronal tissues, several populations of nicotinic receptors have been identified which, although they share a nicotinic pharmacology, have unique characteristics. The alpha-bungarotoxin-insensitive neuronal nicotinic receptors, which may be involved in mediating neuronal excitability, bind nicotinic agonists with high affinity but do not interact with alpha-bungarotoxin. Subtypes of these alpha-toxin-insensitive receptors appear to exist, as evidenced by findings that some are inhibited by neuronal bungarotoxin whereas others are not. In addition to the alpha-bungarotoxin-insensitive sites, alpha-bungarotoxin-sensitive neuronal nicotinic receptors are also present in neuronal tissues. These latter receptors bind alpha-bungarotoxin with high affinity and nicotinic agonists with an affinity in the microM range. The function of the nicotinic alpha-bungarotoxin receptors are as yet uncertain. Thymopoietin, a polypeptide linked to immune function, appears to interact specifically with nicotinic receptor populations that bind alpha-bungarotoxin. Thus, in muscle tissue where alpha-bungarotoxin both binds to the receptor and blocks activity, thymopoietin also potently binds to the receptor and inhibits nicotinic receptors-mediated function. In neuronal tissues, thymopoietin interacts only with the nicotinic alpha-bungarotoxin site and not the alpha-bungarotoxin-insensitive neuronal nicotinic receptor population. These observations that thymopoietin potently and specifically interacts with nicotinic alpha-bungarotoxin-sensitive receptors in neuronal and muscle tissue, together with findings that thymopoietin is an endogenously occurring agent, could suggest that this immune-related polypeptide represents a ligand for the alpha-bungarotoxin receptors. The function of thymopoietin at the alpha-bungarotoxin receptor is as yet uncertain; however, a potential trophic, as well as other roles are suggested.

Binding of thymopoietin to the acetylcholine receptor

Thymopoietin is a polypeptide hormone of the thymus with physiological effects on the immune system and on acetylcholine-mediated transmission at the neuromuscular synapse. Elucidation of the structure and function of the nicotinic acetylcholine receptor has been facilitated by the use of the electric organs of Torpedo ray or Electrophorus eel as rich sources of the receptor and by the use of snake polypeptide toxins such as alpha-bungarotoxin as highly selective labels of the acetylcholine binding site. We now show that thymopoietin binds with high affinity (Ka approximately equal to 2.5 X 10(9) M-1) to the acetylcholine binding region of the acetylcholine receptor of Torpedo californica, as evidenced by similar and complete inhibition of the binding of radiolabeled thymopoietin or alpha-bungarotoxin by either of these polypeptides. These findings raise intriguing questions concerning the mechanisms whereby alpha-bungarotoxin and the thymopoietin affect acetylcholine receptor function, since these two polypeptides with such similar binding properties have very different functional effects.

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.

Identification of thymostimulin secreting cells in calf thymus by immunoperoxidase method

An anti- thymostimulin (TS) serum was tested on calf thymus to study the localization of the hormonal factor. The immunoperoxidase method was applied to tissue fixed in Bouin's fluid and embedded in paraffin, or to tissue fixed in paraformaldehyde and embedded in Epon for semi-thin sections. Immuno-reactivity was shown, with DAB- Fluka , in reticulo-epithelial cells in the medulla, and between the cortex and the medulla, while with DAB-Sigma reactivity was found in the cortex as well. The external cells of Hassall's corpuscles were also reactive. Myoid cells were not reactive. In semi-thin sections a weak reactivity was noted at the periphery of a few lymphocytes. Comparison with the localization of other thymic factors, and the possibility of a functional cycle of the epithelial cells synthesizing one or more factors are discussed.

Generation of a monoclonal antibody against facteur thymique serique (FTS)

A monoclonal antibody against one of the thymic hormones, facteur thymique serique (FTS), was generated by hybridization between mouse NS-1 myeloma cells and BALB/c splenocytes, the latter obtained from BALB/c mice immunized with synthetic FTS coupled to mouse IgG. Enzyme-linked immunosorbent assay (ELISA) was developed and employed to detect the hybridoma secreting specific antibody. The monoclonal antibody (MA-FTS) was highly specific for FTS and did not cross-react with other thymic hormones or other unrelated peptides. MA-FTS could recognize FTS (or FTS-like molecule) in human serum and could absorb completely the FTS-like activity from human serum.

Induction and augmentation of mitogen-induced immune interferon production in human peripheral blood lymphocytes by N alpha-desacetylthymosin alpha 1

Treatment of human peripheral blood lymphocytes with cloned N alpha-desacetylthymosin alpha 1 induced interferon production. The kinetics is similar to that of mitogen-induced interferon induction. N alpha-desacetylthymosin alpha 1, in combination with mitogen, augments the amount of interferon produced. This interferon is immune interferon (IFN-gamma) as determined by sensitivity to pH 2, lack of neutralization by antibodies to IFN-alpha or IFN-beta and absence of activity of MDBK cells. Although the mechanism of induction of IFN-gamma by N alpha-desacetylthymosin alpha 1 is unclear, this compound is not mitogenic at concentrations causing IFN-gamma production. These results indicate that thymic factors may also participate in the regulation of IFN-gamma-production.

Evaluation of functional thymic hormones in Arabian horses with severe combined immunodeficiency

Arabian horses with severe combined immunodeficiency disease (SCID) were evaluated for thymic hormone activities using thymic extracts and sera. Extracts prepared from thymus of SCID horses were able to increase the number of spleen cells responding to sheep red blood cells in irradiated, bone marrow-reconstituted mice. In addition, ultrafiltrates prepared from sera of these immunodeficient horses, which contained material with molecular weight of less than 50,000 Daltons could (a) induce a population of human bone marrow precursor cells to differentiate into cells bearing SRBC receptors and form spontaneous E-rosettes, a characteristic of T lymphocytes, and (b) stimulate cyclic adenosine monophosphate (AMP) synthesis in mouse thymocytes. Based on in vivo and in vitro effects, it was concluded that the defect of these Arabian horses with severe combined immunodeficiency disease did not involve a complete thymic hormone inadequacy.

Selective defects in T cell function in ataxia-telangiectasia

We have studied three patients with ataxia-telangiectasia (AT) and found two of them to have a normal mixed leucocyte culture stimulating and responding ability. However, all three patients and one parent had defective cell-mediated lympholysis (CML), even in the face of a potent proliferative response to allogeneic leucocytes. None of these patients showed significant proliferative responses to common microbial antigens (tetanus toxoid, Candida albicans, purified protein derivative (PPD), diphtheria toxoid, influenza). Our studies indicate tha the T cell defect in AT preferentially affects certain T cell functions associated with antigen recognition and the generation of allogeneic CML, while sparing the allogeneic proliferative response. The selective deficiency of specific lymphocyte functions in a thymic immunodeficiency with a known defect in DNA repair is consistent with the concept that DNA modulating enzymes are important for T cell function.

A synthetic pentapeptide with biological activity characteristic of the thymic hormone thymopoietin

The pentapeptide arginyl-lysyl-aspartyl-valyl-tyrosine, corresponding to amino acid residues 32--36 in thymopoietin, was synthesized. In vitro, this pentapeptide induced the differentiation of murine prothymocytes to thymocytes and inhibited differentiative induction of cells of the B lineage. This combination of actions is presently unique to the parent molecule thymopoietin. In vivo, the pentapeptide reduced the high numbers of autologous rosette-forming cells normally present in the spleens of athymic mice; this also is a property of thymopoietin. These results suggest that this readily synthesized pentapeptide corresponds to an active site of thymopoietin and might serve as a therapeutic substitute for thymopoietin.

Thymic hormones

The thymus produces several polypeptides, which induce lymphocyte differentiation in vitro and in vivo. Several of these polypeptides have been chemically characterized, and three of them have been sequenced and synthesised (alpha 1 thymosin, thymopoietin and the serum thymic factor). Thymic hormones do not act identically on all T-cell subsets: they alter preferentially post-thymic precursor cells, and among mature T cells cytotoxic cells and suppressor cells. Their mode of action at the cellular level involves binding to specific cellular receptors and interaction with adenyl cyclase. Preliminary clinical trials with crude extracts have provided promising results in immunodeficient and cancer patients. The differentiation of T cells from stem cells has been the matter of considerable investigation over the last two decades, since it has been realized that the thymus and its products, the thymus-derived cells (T cells) play a central role in the generation of effector cells in cell-mediated immunity and in the regulation of the various categories of immune responses. That the thymus could act by the intermediate of humoral substances was precociously suggested by MILLER and OSOBA before the observation that thymuses grafted within a cell-impermeable Millipore diffusion chamber restored the immunocompetence of neonatally thymectomized (Tx) mice (1). However, although this experiment was ultimately confirmed by using chambers with well-controlled impermeability (2), MILLER did not pursue the idea of the humoral function of the thymus. Probably, the striking results obtained by DAVIES (3) and other workers, indicating direct migration of functional T cells from the thymus and the poor results initially obtained in trying to reconstitute the immune system of neonatally Tx mice by cell-free thymic extracts contributed to this disappointment. A new impetus was given to the subject in the early 70's when in vitro tests of lymphocyte function became available and when purified extracts of the thymus proved capable of restoring antigen-specific and non-specific immunocompetence of Tx mice. More recently, completely defined synthetic thymic hormones have been obtained. The question is no longer to decide whether thymic hormones exist, but rather to elucidate their biological significance and potential clinical applications. The multiplicity of available factors has created some confusion. It will be the aim of these few pages to review critically the various factors reported in the literature, giving particular emphasis to their pharmacology and their potential use in the modulation of immune responses.

Plasma thymic hormone activity in patients with chronic mucocutaneous candidiasis

To further characterize the immunological abnormalities in patients with chronic mucocutaneous candidiasis, the thymic hormone activity in their plasma was measured. Of the sixteen patients in the study, seven had chronic diffuse candidiasis, five had candidiasis with endocrinopathies and four had candidiasis with thymoma. Only one patient, an anergic child with chronic diffuse candidiasis had severe deficiency of plasma thymic hormone activity. Two patients, a woman with candidiasis and multiple endocrinopathies and an elderly man with metastatic epithelial thymoma had supranormal values.

These studies indicate that the immunological deficit in most patients with these forms of chronic mucocutaneous candidiasis is not due to deficiency of a thymic inductive activity and suggest that an intrinsic defect exists in the maturation of antigen-responsive lymphoid cells.