Thymic hormones--a clinical update

Neonatal thymulin gene therapy prevents ovarian dysgenesis and attenuates reproductive derangements in nude female mice

Congenitally athymic (nude) female mice show severe ovarian dysgenesis after puberty, which seems to be consequential to a number of neuroendocrine derangements described in these mutants. Thus, considerable evidence suggests that thymulin, a thymic peptide, may be involved in thymus-pituitary communication. In order to clarify the relevance of thymulin for the maturation of the female reproductive system, we assessed at hypothalamic, pituitary, ovarian, and uterine level the preventive action of neonatal thymulin gene therapy (NTGT) on the changes that typically occur after puberty in congenitally athymic female mice. We injected (im) an adenoviral vector harboring a synthetic DNA sequence encoding a biologically active analog of thymulin, methionine-serum thymic factor, in newborn nude mice (which are thymulin deficient) and killed the animals at 70-71 d of age. NTGT in the athymic mice restored the serum thymulin levels. Morphometric analysis revealed that athymic nudes have reduced numbers of brain GnRH neurons and pituitary gonadotropic cells as compared with heterozygous controls. NTGT prevented these changes and also rescued the premature ovarian failure phenotype typically observed in athymic nude mice (marked reduction in the number of antral follicles and corpora lutea, increase in atretic follicles). Serum estrogen, but not progesterone, levels were low in athymic nudes, a reduction that was partially prevented by NTGT. Little to no morphological changes were observed in the endometrium of female nudes. The delay in the age of vaginal opening that occurs in athymic nudes was significantly prevented by NTGT. Our results suggest that thymulin plays a relevant physiologic role in the thymus-hypothalamo-pituitary-gonadal axis.

Expression, purification and characterization of a novel soluble human thymosin alpha1 concatemer exhibited a stronger stimulation on mice lymphocytes proliferation and higher anti-tumor activity

Thymosin alpha 1 (Tα1) has immunomodulatory and anti-tumor effects in patients and has been commercialized in worldwide. An innovative technique is therefore impending to achieve high-yield expression and purification of Tα1 to meet the increasing requirements for clinical applications. Tα1 can enhance T cells, dendritic cells and antibody responses, and also augment an anti-tumor immune response. In the current study, we developed a novel technique to produce Tα1 concatemer and investigated its capability in anti-tumor immunotherapy. We expressed the recombinant 2×Tα1 concatemer protein (Tα1② protein) in Escherichia coli. The purity of Tα1② was higher than 95% as assessed by HPLC analysis. In vitro, Tα1② could stimulate the proliferation of mouse splenic lymphocyte, and increase the apoptosis of tumor cell lines. In vivo, Tα1② significantly inhibited the tumor growth in B16 tumor-bearing mice. Compared with Tα1, the Tα1② is of more effective bioactivity than Tα1. The purified Tα1② is a promising substitute for synthetic Tα1 because of its potent anti-tumor effects. We concluded that the expression system for Tα1 concatemer was constructed successfully, which could serves as a highly efficient tool for the production of large quantities of the highly active protein.

Thymulin-based gene therapy and pituitary function in animal models of aging

Thymulin is a thymic hormone exclusively produced by the thymic epithelial cells. After its discovery and initial characterization in the 1970s, it was demonstrated that thymulin production and secretion is strongly influenced by the neuroendocrine system. Conversely, a growing core of information, to be reviewed here, points to thymulin as a hypophysiotropic peptide. Additionally, thymulin was shown to possess anti-inflammatory and analgesic properties in the brain. In recent years, a synthetic DNA sequence coding for a biologically active analog of thymulin, metFTS, was constructed and cloned in different adenoviral vectors. These include bidirectional regulatable Tet-Off vector systems that simultaneously express metFTS and green fluorescent protein and that can be downregulated reversibly by the addition of the antibiotic doxycycline. A number of recent studies suggest that thymulin gene therapy may be a suitable therapeutic strategy to prevent some of the endocrine and reproductive alterations that typically appear in congenitally athymic (nude) mice, taken as a suitable model of neuroendocrine and reproductive aging. The present article briefly reviews the literature on the physiology of the thymulin-pituitary axis as well as on the new molecular tools available to exploit the therapeutic potential of thymulin.

The thymus-neuroendocrine axis: physiology, molecular biology, and therapeutic potential of the thymic peptide thymulin

Thymulin is a thymic hormone exclusively produced by the thymic epithelial cells. It consists of a nonapeptide component coupled to the ion zinc, which confers biological activity to the molecule. After its discovery in the early 1970s, thymulin was characterized as a thymic hormone involved in several aspects of intrathymic and extrathymic T cell differentiation. Subsequently, it was demonstrated that thymulin production and secretion is strongly influenced by the neuroendocrine system. Conversely, a growing core of information, to be reviewed here, points to thymulin as a hypophysotropic peptide. In recent years, interest has arisen in the potential use of thymulin as a therapeutic agent. Thymulin was shown to possess anti-inflammatory and analgesic properties in the brain. Furthermore, an adenoviral vector harboring a synthetic gene for thymulin, stereotaxically injected in the rat brain, achieved a much longer expression than the adenovirally mediated expression in the brain of other genes, thus suggesting that an anti-inflammatory activity of thymulin prevents the immune system from destroying virus-transduced brain cells. Other studies suggest that thymulin gene therapy may also be a suitable therapeutic strategy to prevent some of the endocrine and metabolic alterations that typically appear in thymus-deficient animal models. The present article briefly reviews the literature on the physiology, molecular biology, and therapeutic potential of thymulin.

Efficacy of thymosin alpha-1 and interferon alpha in treatment of chronic viral hepatitis B: A randomized controlled study

AIM: To observe the efficiency and safety of thymosin-α1 treatment in patients with hepatitis B e antigen (HBeAg) and HBV DNA positive chronic hepatitis.

METHODS: Sixty-two patients were randomly divided into groups A and B. The patients in group A received subcutaneous injection of 1.6 mg thymosin-α1, twice a week (T-α1 group) for six months, and the patients in group B received 5 MU interferon alpha (IFN-α) each day for fifteen days, then three times weekly (IFN-α group) for six months. The results between two groups treated with and the group untreated with IFN-α which was followed up for 12 mo (historical control group consisting of 30 patients) were compared, and three groups were comparable between each other (P > 0.05) at baseline (age, sex, clinical history, biochemical, and serological parameters).

RESULTS: At the end of treatment, complete response, which was defined as alanine aminotransferase (ALT) normalization and HBV DNA and HBeAg loss, occurred in 9 of 29 (31.0%) patients in the T-α1 group and in 15 of 33 (45.5%) patients in the IFN-α group (χ² = 1.36, P > 0.05). After a follow-up period of six months, a complete response was observed in 14 of 29 (48.3%) patients in the T-α1 group and in 9 of 33 (27.3%) patients in the IFN-α group (χ² = 2.93, P > 0.05). Compared with the results observed in the historical control (HC) group untreated with IFN-α which was followed up for 12 mo, the rate of complete response was significantly higher in IFN-α group at the end of therapy (1 of 30 vs 15 of 33, χ² = 14.72, P < 0.001) and in the T-α1 group at the end of follow-up (1 of 30 vs 14 of 29, χ² = 15.71, P < 0.001). In T-α1 and IFN-α treatment groups, the area under (the plasma concentration time) curve (AUC) of negative HBV DNA and HBeAg was 34%, 17%, 31% and 19% smaller than that in the HC group. By the end of the follow-up period, the proportions of ALT normalization and negative HBV DNA in the T-α1 group were significantly higher than those in the IFN-α and HC groups. The odds of ALT normalization and negative HBV DNA at the end of the follow-up was three-fold higher in the T-α1 group than in the IFN-α group. Unlike IFN-α, T-α1 was well tolerated by all patients, and no side effects appeared in T-α1 group.

CONCLUSION: The results suggest that a 6-mo course of T-α1 therapy is effective and safe in patients with chronic hepatitis B. T-α1 is able to reduce HBV replication in patients with chronic hepatitis B. Furthermore, T-α1 is better tolerated than IFN-α and can gradually induce more sustained ALT normalization and HBV DNA and HBeAg loss. However, a response rate of 48.3% is still less ideal. A more effective therapeutic approach warrants further study.

Roles of thymosins in cancers and other organ systems

Thymosins are small peptides, originally identified from the thymus, but now known to be more widely distributed in many tissues and cells. Thymosins are divided into three main groups, alpha-, beta-, : and gamma-thymosins, based on their isoelectric points. alpha-thymosins (ProTalpha, Talphal) have nuclear localization and are involved in transcription and/or DNA replications; whereas beta-thymosins (Tbeta4, Tbeta10, Tbetal5) have cytoplasmic localization and show high affinity to G-actin for cell mobility. Furthermore, it is well known that both alpha- and beta-thymosins play important roles in modulating immune response, vascular biology, and cancer pathogenesis. More importantly, thymosins may have significant clinical applications. They may serve as molecular markers for the diagnosis and prognosis of certain diseases. In addition, they could be molecular targets of certain diseases or be used as therapeutic agents to treat certain diseases. However, the molecular mechanisms of action of thymosins are largely unknown. This review not only presents recent advances of basic science research of thymosins and their clinical applications but provides thoughtful views for future directions of investigation on thymosins.

A randomized, controlled, clinical study of thymosin alpha-1 versus interferon-alpha in [corrected] patients with chronic hepatitis B lacking HBeAg in China [corrected]

BACKGROUND

This study was designed to compare the efficacy and safety of thymosin-alphal (T-alpha1) with that of interferon-alpha (IFN-alpha) in patients with chronic hepatitis B who were positive for hepatitis B virus (HBV) DNA and hepatitis B envelope antibody (anti-HBe).

METHODS

Fifty-six patients were randomly divided into groups A and B. Both groups were comparable (p > 0.05) at baseline regarding age, sex, and alanine aminotransferase (ALT) levels. Group A patients received T-alpha1 1.6 mg subcutaneously twice weekly, while group B patients received IFN-alpha 5 million IU daily for 15 days, then thrice weekly for 6 months. Results from the 2 groups were compared with data from a group of 30 patients never treated with IFN-alpha and who were followed-up for 12 months (historical control [HC] group); the 3 groups were comparable (p > 0.05).

RESULTS

After treatment, a complete response (ALT normalization and HBV DNA loss) occurred in 8 of 26 patients in group A (30.8%) and 14 of 30 in group B (46.7%; chi2 = 1.476, p = 0.224). After a follow-up period of 6 months, a complete response was observed in 11 of 26 patients in group A (42.3%) and 7 of 30 in group B (23.3%; chi2 = 2.299, p = 0.129). The rate of complete response was significantly greater in the IFN-alpha than HC group at the end of therapy (46.7% vs 3.3%; chi2 = 15.022, p = 0.0001), and in the T-alphal than HC group at the end of follow-up (42.3% vs 3.3%; chi2 = 12.566, p = 0.0001). Ten of the 12 T-alphal responders (i.e. partial responders; 83.3%) experienced sustained, non-detectable HBV DNA after 6 months' treatment; 6 of the 14 T-alphal non-responders (42.9%) showed a delayed response of non-detectable HBV DNA during the follow-up period. Corresponding values for group B patients were 50% (9/18) and 0% (0/12). The rate of delayed response was significantly higher in group A than the other 2 groups (chi2 = 6.686, p = 0.010; chi2 = 4.964, p = 0.038), whereas the rate of flare was higher in group B than in the other 2 groups (chi2 = 3.445, p = 0.063; chi2 = 7.668, p = 0.006), during the follow-up period. Unlike IFN-alpha, T-alphal was well tolerated, i.e. no adverse effects were noted in group A.

CONCLUSION

These results suggest that a 6-month course of T-alpha1 therapy is effective and safe in patients with anti-HBe-positive chronic hepatitis B; T-alpha1 can reduce HBV replication in such patients. Compared with IFN-alpha, T-alpha1 is better tolerated and seems to induce a gradual and more sustained normalization of ALT and loss of HBV DNA. Combination therapy with T-alpha1 and IFN-alpha or nucleoside analogs for hepatitis B warrants further study.

Long-term outcomes of thymosin-alpha 1 and interferon alpha-2b combination therapy in patients with hepatitis B e antigen (HBeAg) negative chronic hepatitis B

Hepatitis B e antibody (HbeAb) and hepatitis B virus (HBV) DNA positive chronic hepatitis is a clinical entity, distinct from classical hepatitis B e antigen (HbeAg) positive chronic hepatitis B. Our aim was to evaluate the long-term therapeutic efficacy of the combination of interferon alpha-2b and thymosin-alpha1 compared with lamivudine plus interferon alpha-2b and interferon alpha-2b alone. Fifty-two patients with HbeAg-negative chronic hepatitis B were assigned to three different groups in a nonrandomized manner. Group 1 (n = 27) received thymosin-alpha1 [1.6 mg subcutaneously (sc), twice a week] and interferon alpha-2b (10 MIU sc, three times per week) for 26 weeks, subsequently followed by interferon alpha-2b monotherapy at the same dosage for an additional 26 weeks. Group 2 (n = 10) received interferon alpha-2b (10 MIU sc, three times per week) for 52 weeks. Group 3 (n = 15) received interferon alpha-2b (10 MIU sc, three times per week) and lamivudine [100 mg orally (po), q.d.] for 52 weeks, followed by continuous lamivudine (100 mg po, q.d.) therapy. By the end of 78 weeks, a sustained response (SR-6 mo) was seen in 74% (20/27) of the patients within Group 1. On the contrary, Groups 2 and 3 had sustained response rates of 40 (4/10) and 53.3% (8/15), respectively (p = 0.13). At the end of 12 months post-treatment in Group 1, a virological and biochemical response rate was seen in 70.3% of patients (19/27); in contrast, Groups 2 and 3 had response rates of 20 (2/10) and 26.6% (4/15), respectively (p = 0036). At the end of the 18-month post-treatment follow-up period, 71.4% (19/27) of patients in Group 1, 10% of patients in Group 2 (1/10), and 20% of patients in Group 3(3/15) preserved their sustained response (p = 0.0003). Interferon alpha-2b and thymosin-alpha1 combination therapy results in significant virological and biochemical response rates compared with standard therapeutic regimens and is well tolerated.

Interrelationships among brain, endocrine and immune response in ageing and successful ageing: role of metallothionein III isoform

Metallothionein-III (MT-III) a brain-specific member of metallothionein family contributes to zinc neuronal homeostasis, and zinc is an important regulator of many brain functions, including the activity of hormone realising factors by hippocampus. Among them, somatostatin is pivotal because affecting thyroid hormones turnover and consequently thymic and peripheral immune efficiency (Natural Killer, NK) cell activity. Somatostatin is in turn affected by somatomedin-C, which is also zinc-dependent. Therefore, somatomedin-C may be a marker of somatostatin status in the hippocampus. MTs sequester and release zinc in transient stress, as it may occur in young age, to protect cells by reactive oxygen species. In order to accomplish this task, MTs are induced by IL-6 for a prompt immune and anti-inflammatory response. During ageing, MTs are high with a role of sequester of zinc, but with very limited role in zinc release because stress-like condition and inflammation is persistent. Therefore, high MTs may become to protective in young age to harmful during ageing leading to low zinc ion bioavailability for many body homeostatic mechanisms, including brain function. As a consequence, an altered physiological cascade from the brain (upstream) to endocrine and immune system (downstream) may occur. The aim of this work is to study the role of MT-III in the interrelationships among brain-endocrine-immune response in ageing and successful ageing. The main results are: (1) MT-III and IL-6 gene expressions increase in the hippocampus from old mice, in comparison with young and very old mice. (2) Somatomedin-C plasma levels decrease in old mice in comparison with young and very old mice. (3) Low zinc ion bioavailability (tested by the ratio total thymulin/active thymulin) is coupled with altered thyroid hormone turnover and depressed IL-2 in old mice in comparison with young and very old mice. (4) 'In vitro' experiments display more increments on NK cells activity by adding zinc-bound active thymulin than T3 alone. In conclusion, low MT-III in the hippocampus from young and very old mice leads to good zinc ion bioavailability that it is upstream coupled with normal hippocampal function affecting downstream normal thyroid hormones turnover and satisfactory NK cell activity, via complete saturation of zinc-bound active thymulin molecules. Therefore, a correct MTs homeostasis is pivotal for brain-endocrine-immune response in order to reach successful ageing.

Thymosin alpha1 accelerates restoration of T cell-mediated neutralizing antibody response in immunocompromised hosts

Thymosin alpha1 is a biological response modifier that has been used clinically for the treatment of chronic hepatitis B viral infection. Both immunomodulatory and immediate intracellular mechanisms have been postulated to explain the effect of thymosin alpha1 on hepatocytes infected with hepatitis B virus (HBV). Here, we established a new animal model and the related suitable conditions to access the thymosin activity by means of measuring the production of neutralizing antibody against hepatitis B surface antigen (HBsAg). We proved that chemically synthesized thymosin alpha1 restored the T cell-mediated antibody production following its suppression in mice by 5-fluorouracil (5-FU), and found that thymosin alpha1 showed activity at a low dose of 30 microg/kg. Further studies utilizing the flowcytometric analysis showed that thymosin alpha1 at this dose accelerated the replenishment and maturation of thymocytes while the expression of Smoothened (Smo) of the Hedgehog (Hh)-signaling in CD4-CD8- thymocytes, the potent negative regulator of proliferative responses, was not affected. The restoration of some of the defects in the host defense systems may facilitate elimination of infectious agents, and the present study provides a novel model to define the restoration of T cell-mediated immune responses to hepatitis B virus in vivo.

Review: Present and future directions in the treatment of chronic hepatitis B infection

The last decade has witnessed substantial progress in the development of chemotherapeutic agents for chronic hepatitis B. However, the only currently licensed treatment in Australia, interferon-alpha, has low initial response rates and the adverse effects are often unacceptable. Of the newer agents in the class of nucleoside analogues, famciclovir and lamivudine are in phase III clinical trials with encouraging preliminary results, while other agents, such as bis-POM PMEA (Adefovir), are at phase I/II development. Future approaches to therapy will be governed by an understanding of the effects of nucleoside analogues on the natural history of the disease as well as on the hepatitis B virus hepatocyte interaction. Combination antiviral therapy should theoretically offer improved response rates, decrease the development of viral resistance, and provide the greatest reduction in viral load, but it has not yet been widely examined in the clinical setting. In this article, we review the currently available strategies, discuss potential problem areas, and speculate on promising approaches with combination chemotherapy and the features of agents soon to be trialed.

Primary antiphospholipid syndrome emerging following thymectomy for myasthenia gravis: additional evidence for the kaleidoscope of autoimmunity

The etiology of autoimmune diseases is multifactorial. In many of them the stimulation by a specific autoantigen is claimed to be responsible for the initiation of the disease. Alternatively, an autoimmune state may be induced by a pure dysregulation of the immune system. Such is the case in which severe systemic lupus erythematosus (SLE) is induced in young patients with myasthenia gravis following thymectomy. We have referred to this set of events as the 'kaleidoscope of autoimmunity'. Herewith, we would like to present another example of the kaleidoscope phenomenon, namely: the emergence of a full blown clinical presentation of the primary antiphospholipid syndrome (APS-recurrent thromboembolic phenomena, repeated fetal loss with high titers of anti-cardiolipid antibodies) in a 32 y old female with myasthenia gravis, two years following thymectomy. Thymectomy in myasthenic patients may be associated with the emergence of new autoimmune conditions such as SLE and APS, pointing to the importance of immune dysregulation in the induction of these autoimmune diseases.

A double-blind, placebo-controlled, pilot trial of thymosin alpha 1 for the treatment of chronic hepatitis C

A randomized, double-blind, placebo-controlled trial was performed to evaluate the efficacy and safety of thymosin alpha 1 (alpha 1) in treating chronic hepatitis C. Nineteen Italian patients with chronic active hepatitis C, proven by biopsy were randomly assigned to receive a six month course of thymosin alpha 1 (900 micrograms/m2 of body surface area twice weekly) or a placebo. All had HCV-RNA in their serum (by PCR), with serum ALT levels more than double the upper limit of the normal range for at least six months before enrollment. After treatment, patients were followed for an additional six months. All patients completed the trial. One patient treated with thymosin alpha 1, but no patient in the placebo group, normalized serum ALT levels by the end of the treatment. This patient, however, relapsed at the sixth month of the follow up. Overall, there were no significant changes in mean serum ALT levels in either group during the treatment or follow-up period. No patient cleared HCV-RNA. No side effects were reported except for local discomfort at the injection sites, reported by some patients treated with thymosin alpha 1. In conclusion, this regimen of thymosin alpha 1 is not effective in the treatment of chronic hepatitis C.

Prospectives on the treatment of chronic hepatitis B and chronic hepatitis C with thymic peptides and antiviral agents

At the present time, interferon is considered the only effective therapeutic approach in the treatment of both chronic hepatitis B and chronic hepatitis C. It is clear that the disappointing response rates in both chronic hepatitis B and C place added emphasis on efforts to identify alternative forms of therapy. In addition to the development of other antiviral agents including the nucleoside analogs which might prove more effective and have fewer associated side-effects, other agents currently under investigation include thymic peptides such as thymosin alpha 1. In the future, the therapeutic approach to the treatment of chronic hepatitis B and C may consist of combination therapy using perhaps an immune modulator and an antiviral agent or, several antiviral drugs. Alternatively, there is indication that cellular targeting systems with delivery of the toxic material to the specific cell containing the virus may be more effective, while minimizing side-effects. Finally, there are agents such as ursodeoxycholic acid which perhaps, makes bile less toxic and can be used as adjunctive therapy with improvement in liver chemistry values. The treatment of chronic hepatitis B and chronic hepatitis C has shifted in emphasis form the concept of treating liver disease towards that of treating viral infections which happen to effect primarily the liver.

Neuromodulatory loop mediated by nerve growth factor and interleukin 6 in thymic stromal cell cultures

Neural crest cell derivatives have been suggested to be involved in thymus development. We established nonlymphoid thymic stromal cell cultures capable of supporting T-cell differentiation. In these nonlymphoid cell cultures, we identified cells with phenotypic and biochemical markers specific for neuronal cells. Neurofilament mRNA and 68- and 160-kDa neurofilament proteins, as well as 74-kDa synapsin I isoform, were expressed in many of the cultured cells. For example, neurofilament immunoreactivity was detected in 20-30% of the cells. To see whether thymic neuronal-like cells were involved in a neural differentiation pathway, we investigated the effect of nerve growth factor (NGF) and interleukin 6 (IL-6), two known neurotrophic factors. The expression of the above-described neural markers was enhanced by NGF and IL-6, which we report to be produced in an autocrine way by thymic stromal cell cultures. Finally, we found that IL-6 gene expression in these cell cultures was enhanced by NGF. Evidence is thus offered of a neuromodulatory loop within the thymic stromal cell population supported by local production of NGF and IL-6 and involving neural cell elements. Interestingly, IL-6, which is known to be implicated in thymocyte differentiation, also displays a neuromodulatory activity on thymic stromal cells, suggesting a multivalent role for this cytokine within the thymus.

Evidence for the extranuclear localization of thymosins in thymus

A new radioimmunoassay has been developed for thymosin beta 4 by generating rabbit polyclonal antibodies against the synthetic N-terminal peptide fragment 1-15 coupled to KLH. The synthetic analogue [Tyr12]-thymosin beta 4 (1-15) was used as tracer. This radioimmunoassay, with a useful range of 10-1000 pmoles, showed cross-reactivity with the second homologous beta-thymosin of man and rat (thymosin beta 10) but not of calf (thymosin beta 9). This radioimmunoassay, together with an improved radioimmunoassay for the N-terminus of parathymosin alpha, was employed for the measurement of the levels of thymosin beta 4 and parathymosin alpha in nuclear and extranuclear extracts of calf thymus. The bulk of these polypeptides was found in the extranuclear material whereas only traces were observed in the nuclear environment, which indicates the extranuclear localisation of alpha- and beta-thymosins.

Effects of the immunomodulator diacetyl-splenopentin on antigen-induced arthritis in rabbits

Long-term treatment with the immunomodulator diacetyl-splenopentin reduces the severity of chronic joint inflammation and cartilage destruction in rabbits with antigen-induced arthritis. The level of specific antibodies as well as specific and non-specific cell-mediated immune reactivities including the proliferative response of spleen lymphocytes to cartilage proteoglycans in treated animals are lower than in untreated arthritic rabbits. Moreover, suppressor cell activity, which normally decreases during the early phase of inflammation, is enhanced and hyperreactive helper cell potential is reduced. These findings suggest that treatment with diacetyl-splenopentin normalizes the immune regulation, which is disturbed in the early phase of inflammation. This might result in a depression of the hyperreactive immune system including the autoimmunity developed against cartilage. Lowered immune reactivity in the joint in turn reduces the severity of chronic joint inflammation.

Prothymosin alpha enhances interleukin 2 receptor expression in normal human T-lymphocytes

We investigated whether the enhancement, by prothymosin alpha (Pro alpha), of the phytohaemagglutinin-stimulated proliferation of human peripheral blood mononuclear cells (PBMC) is due to its affect on the number of cells expressing the interleukin 2 receptor (IL-2R) or the surface density of IL-2R on PBMC. Peripheral blood mononuclear cells were obtained from 21 donors. For both an optimal phytohaemagglutinin (PHA) concentration (H) and a 10-fold dilution (L), their responses fell in two classes, high (h) and low (l), making four dose--response situations. Pro alpha significantly increased the number and IL-2R density of cells expressing IL-2R only when the response in its absence was about half maximal, i.e. for PBMC responding well to the low PHA stimulus (group Lh) or PBMC responding poorly to the optimal stimulus (group Hl). The enhancement of IL-2R expression in group Lh by Pro alpha was dose-dependent and paralleled by increased proliferative response. It appears not to be mediated by IL-2, since it was unaffected when IL-2 production was suppressed by cyclosporin A. The early interaction of Pro alpha with lymphocytes did not require the presence of macrophages, but macrophages were necessary during lymphocyte activation for modulation of PHA-stimulated IL-2R expression to be affected. The immunoregulatory activity of Pro alpha may prove useful for improving the decreased T-cell function associated with immunodeficiency, or for restoration of normal IL-2R expression by the lymphocytes of aged individuals.

Thymosin alpha 1 modulates the expression of high affinity interleukin-2 receptors on normal human lymphocytes

In this report we demonstrate that thymosin alpha 1 (T alpha 1), a synthetic peptide composed of 28 amino acid residues, and thymosin fraction 5 (TF5) enhance the number of high affinity interleukin 2 receptors (IL-2R) expressed by human peripheral blood lymphocytes in response to in vitro stimulation with phytohemagglutinin (PHA). Thymosins did not, however, alter the affinity of the IL-2R for its ligand. Dose-response studies using a wide range of concentrations indicated a bimodal distribution of responsiveness to T alpha 1. In most experiments the high and low concentration peaks of activity were observed at 10(-8) M and 10(-12) M, respectively, although peak responses were observed at different T alpha 1 concentrations in different donors. No effects were elicited by thymosins in the absence of mitogenic stimulation. Thymosin enhancement of PHA-induced high affinity IL-2R expression directly correlated with increased levels of Tac antigen expression, as determined by flow cytometry, and enhanced interleukin 2 (IL-2) production. Since the biological effects of IL-2 are associated with the occupancy of high affinity IL-2R, the findings presented in this report strongly suggest that thymosins play a significant role in the regulation of immune responses through the modulation of high affinity IL-2R expression.

Characterization of the immunoregulatory properties of thymosin alpha 1 on interleukin-2 production and interleukin-2 receptor expression in normal human lymphocytes

Thymosin alpha 1 (T alpha 1) and thymosin fraction 5 (TF5) have been shown to induce lymphocyte maturation and differentiation as well as to modulate mature immune responses to antigens and mitogens. The present study focused on the characterization of the mechanisms involved in T alpha 1 and TF5 enhancement of phytohemagglutinin (PHA)-induced interleukin-2 (IL-2) secretion and interleukin-2 receptor (IL-2R) expression in human mononuclear cells. We provide evidence that TF5 and T alpha 1 modulate an early event(s) during lymphocyte activation by mitogens. A short preincubation period (30 min) of non-adherent cells with thymosins, followed by extensive washing and subsequent exposure to PHA, was sufficient to enhance the production of IL-2 and the expression of IL-2R induced by the mitogen. Furthermore, the concomitant addition of PHA and thymosin during the preincubation period is not necessary for the enhancing effects to occur. We have also studied the role of macrophages on thymosin modulation of these responses. Results presented here indicate that macrophages are not essential for the interaction of thymosins with T-cells. However, macrophages are an absolute requirement during the exposure to the mitogen after preincubation with thymosins for the manifestation of TF5- and T alpha 1-mediated enhancing effects on IL-2 production and IL-2R expression. Human recombinant interleukin-1 beta (rIL-1 beta) was able to replace this macrophage requirement, indicating that production of IL-1 by these cells is a critical event in thymosin modulation of the IL-2 system. Two-color flow cytometric analysis and experiments involving the use of highly purified helper/inducer (Th, CD4+) and cytotoxic/suppressor (Tc, CD8+) T-cell populations indicated that both, Th and Tc cell populations are targets of thymosin activity. These studies provide additional evidence that thymosins play an important role in the modulation of the normal immune response and begin to define the mechanisms underlying T alpha 1 immunoregulatory properties.

The neuroendocrine thymus. Abundant occurrence of oxytocin-, vasopressin-, and neurophysin-like peptides in epithelial cells

Certain subtypes of thymic epithelial cells--the medullary epithelium, the cortical surface epithelium, and some intracortical epithelial cells--show strong immunohistochemical reactivity with antisera against oxytocin, Arg-vasopressin and neurophysin. The epithelial nature of the neuropeptide containing cells is shown by their morphology and their reactivity with monoclonal anti-cytokeratin AE1/E3. Hassall's corpuscles are positive as well. The immunoreactivity patterns for the three neuropeptides are identical, suggesting a parallel distribution. The vast majority of cortical epithelial cells are negative, emphasizing the tightly controlled microenvironment for T-cell development. The possibility of a neuroendocrine role of the thymus is discussed.

In vitro effects of thymosin and lithium on lymphoproliferative responses of normal donors and HIV seropositive male homosexuals with AIDS-related complex

The in vitro effects of thymosin fraction 5 (TF5) and lithium chloride (LiCl) on the ability of peripheral blood mononuclear cells (PBMC) obtained from 37 normal male donors and 33 male patients with AIDS-related complex (ARC) to respond to alloantigenic stimulation (mixed leukocyte reaction, MLR) and to produce interleukin 2 (IL-2) in response to mitogens were studied. TF5 significantly increased MLR responses in normal donors (P less than 0.01) and in a group of 33 ARC patients with depressed cellular immunity (P less than 0.05). Similar effects were observed when LiCl was added to the MLR assays in both the normal and the ARC patient groups. Furthermore, TF5 and LiCl exhibited additive immunoenhancing properties. In 10 normal donors TF5 enhanced phytohemaggutinin (PHA)-induced IL-2 production as well as IL-2 production in response to pokeweed mitogen (PWM) (P less than 0.02). TF5-mediated enhancement of IL-2 production by PBMC obtained from ARC patients was observed in response to both mitogens, i.e., PHA and PWM. Additionally, LiCl increased PHA-induced IL-2 production in both normal subjects and ARC patients. LiCl and TF5 together had an additive effect in the enhancement of IL-2 production in both groups of subjects. Our data extend previous observations regarding the immunoregulatory activities of TF5 and LiCl and provide evidence that PBMC obtained from ARC patients have the potential to respond in vitro to these agents. The significance of these findings is discussed.

Effect of thymostimulin in models of cell-mediated and humoral autoreactivity and on T-dependent suppression

To explore the therapeutic potential of the thymic hormone preparation thymostimulin (TS) in animal models of cell-mediated and humoral autoimmunity, its effects were investigated on experimental allergic encephalomyelitis in guinea pigs and on anti-erythrocytic autoantibody production in C57B1/6 mice. In both autoimmunity models, TS produced significant therapeutic effects in terms of proportion of diseased animals, disease severity and/or disease duration; however, both the TS dose and the time of treatment start relative to the disease-inducing stimulus critically influenced results. TS effects on the generation and expression of suppressive activity induced in C57B1/6 mice by a supraoptimal immunization with 10(10) SRBC were also examined. TS given after 10(10) SRBC did not influence the level of suppression, and the activity of effectors of suppression was not modified by this agent. Conversely, using a treatment protocol analogous to that effective in reducing murine autoantibody production, TS administration prior to 10(10) SRBC was associated with a significant increase in the subsequent generation of T-dependent, antigen-specific suppressive activity. These findings suggest that effects of TS on the development of suppressor cells may be involved in the activity of this agent in animal models of autoaggression.

Modulation of interleukin 2 receptor expression on normal human lymphocytes by thymic hormones

The expression of interleukin 2 receptors (IL-2R) is a critical step leading to normal lymphocyte proliferation. Since thymosin fraction 5 (TF5), a thymic hormone preparation, enhances lymphoproliferative responses of human cells, we examined the effects of TF5 on the expression of IL-2R on mitogen-stimulated human lymphocytes. TF5 significantly increased the percentage and antigen density of cells expressing IL-2R after stimulation with an optimal concentration of phytohemagglutinin (PHA) when the cells from the same donor exhibited suboptimal responses to PHA alone. The same effect was observed with a suboptimal PHA concentration and with OKT3 monoclonal antibody stimulation. Thymosin alpha 1, a synthetic polypeptide originally isolated in its native form from TF5, was also able to increase IL-2R expression in response to PHA, suggesting that it is the active species in TF5. The enhancement of IL-2R expression was paralleled by increased proliferative responses. Increased IL-2R expression appears to be the direct effect of thymic hormones, since abrogation of interleukin 2 production by cyclosporin A did not affect TF5-mediated enhancement of PHA-induced IL-2R expression. These results point to a physiological role of thymic hormones in the maintenance of normal levels of IL-2R expression. This immunoregulatory activity of thymic hormones might be relevant in the treatment of conditions where there is decreased IL-2R expression, such as the acquired immune-deficiency syndrome, or in the restoration of normal IL-2R expression to lymphocytes from aged individuals.