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

Thymic Hormones and Cytokines

The discovery and the first studies on thymic hormones (TH) are historically linked with their role on the developmental events of T lymphocytes that occur within the thymus. However, paradoxically, during the most recent years, much more information about the effects of TH on mature effector cells, in relation with those indicating their real functions during the T-cell differentation, have been, in fact, available.

Here we report an update discussion concerning the possible role of the cooperation between TH and cytokines in T-cell development. Moreover we illustrate the results obtained by us and other authors, demonstrating a strict connection between the action of thymosins, a family of peptides first isolated and purified from calf thymus (1), and that of cytokines.

Immune Modulation with Thymosin Alpha 1 Treatment

Thymosin alpha 1 (Ta1) is a peptide originally isolated from thymic tissue as the compound responsible for restoring immune function to thymectomized mice. Ta1 has a pleiotropic mechanism of action, affecting multiple immune cell subsets that are involved in immune suppression. Ta1 acts through Toll-like receptors in both myeloid and plasmacytoid dendritic cells, leading to activation and stimulation of signaling pathways and initiation of production of immune-related cytokines. Due to the immune stimulating effects of Ta1, the compound would be expected to show utility for treatment of immune suppression, whether related to aging or to diseases such as infection or cancer. Extensive studies in both the preclinical and clinical setting will be summarized in the subsequent sections. These studies have demonstrated improvements in immune system cell subsets and the potential of Ta1 for the treatment of a range of diseases.

Thymosin α1 continues to show promise as an enhancer for vaccine response

Thymosin α1 (Tα1) is an immune-modulating peptide that can be expected to improve response to vaccinations, as stimulated dendritic cells and T cells can act in concert to increase antibody production along with an improved cytotoxic response from the T cells themselves. Tα1 demonstrated efficacy in preclinical studies; subsequently, it was shown to enhance response to vaccinations in difficult-to-treat populations, including individuals immune suppressed due to age or hemodialysis, and leading to a decrease in later infections. During the 2009 pandemic outbreak of H1N1 influenza, mouse and ferret studies confirmed that the use of higher doses of Tα1 allowed for fewer injections than those used in the previous clinical studies. In addition, a clinical study with Focetria™ MF59-adjuvanted monovalent H1N1 vaccine showed that treatment with Tα1 twice provided an earlier and greater response to the vaccine (P < 0.01).

Thymosin α1 and cancer: action on immune effector and tumor target cells

Since it was first identified, thymosin alpha 1 (Tα1) has been characterized to have pleiotropic effects on several pathological conditions, in particular as a modulator of immune response and inflammation. Several properties exerted by Tα1 may be attributable to a direct action on lymphoid cells. Tα1 has been shown to exert an immune modulatory activity on both T cell and natural killer cell maturation and to have an effect on functions of mature lymphocytes, including stimulating cytokine production and cytotoxic T lymphocyte-mediated cytotoxic responses. In previous studies we have shown that Tα1 increases the expression of major histocompatibility complex class I surface molecules in murine and human tumor cell lines and in primary cultures of human macrophages. In the present paper, we describe preliminary data indicating that Tα1 is also capable of increasing the expression of tumor antigens in both experimental and human tumor cell lines. This effect, which is exerted at the level of the target tumor cells, represents an additional factor increasing the antitumor activity of Tα1.

Separation and isolation of fusion protein using a new native preparative PAGE device

A human serum albumin and Thymosin α1 (HSA-Tα1) fusion protein was designed and over-expressed in Pichia pastoris. To purify the fusion protein, a new native preparative electrophoresis system that involved a modified device with a sample receiving chamber, and an assay method with Coomassie Blue G-250 tracing the collection of the protein of interest. In this device, two gels were run in parallel: native vertical collecting polyacrylamide gel electrophoresis (PAGE) and native vertical tracing PAGE. Samples mixed with or without Coomassie Blue G-250 loading buffer were separately loaded to the two aforementioned gels, and the fractions were collected until the tracing protein band combined with dye reached 1 cm from the sample-receiving chamber at the bottom of the gel. Approximately nine fractions were collected at regular intervals of 15 min. HSA-Tα1 fusion protein with 95% relative homogeneity was harvested and manifested similar immunological activities as synthetic Tα1 after a single-step purification of this preparative PAGE. As a result, this system offers a new, rapid and simple method for the purification of the protein of interest.

Thymosin Alpha-1 in Combination with Pegylated Interferon and Ribavirin in Chronic Hepatitis C Patients Who have Failed to Prior Pegylated Interferon and Ribavirin Treatment

Combination therapy with inteferon-alpha and ribavirin is an approved therapy for patients with chronic hepatitis C. However, even with the use of pegylated interferon, response rates are still poor in many difficult-to-treat groups, especially with genotype 1 and high viral loads. Retreatment of these patients remains challenging. Newer combinations are being investigated to optimize chances of attaining a sustained response in these groups. Thymosin alpha 1 is a polypeptide with immunomodulatory properties that has been suggested to increase response rates in patients with chronic hepatitis C. Herein, we describe two cases of retreatment patients with chronic hepatitis C who have failed prior pegylated interferon and ribavirin therapy. They received triple combination therapies of thymosin alpha 1, pegylated interferon and ribavirin and achieved sustained virological responses. These cases support that thymosin-alpha 1 may increase the efficacy of pegylated interferon plus ribavirin in the treatment of non-responders to previous combination therapy.

Zadaxin (thymosin alpha1) for the treatment of viral hepatitis

Zadaxin (thymosin alpha1; Talpha1) is a synthetic 28 amino acid peptide with multiple biological activities primarily directed towards immune response enhancement. Since the immune system plays a critical role in the control and elimination of viral hepatitis infection, immune active agents such as Talpha1 are of potential therapeutic value. In clinical trials, Talpha1 has been shown to be effective in chronic hepatitis B, both asmonotherapy and in combination with interferon-alpha (IFN-alpha). In chronic hepatitis C it was effective in combination with IFN-alpha. Since Talpha1 has few side-effects and is effective in combination with IFN-alpha, future clinical trials should evaluate the potential of Talpha1 to enhance the activity of antivirals such as IFN-alpha, ribavirin and lamivudine as viral hepatitis therapy.

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.

Thymosin-alpha 1 plus interferon-alpha for naive patients with chronic hepatitis C: results of a randomized controlled pilot trial

In this pilot study, we evaluated the efficacy of interferon-alpha (IFN) plus Thymosin-alpha 1 (TA1) to that of IFN alone in naive patients with chronic hepatitis C. Twenty-two patients were randomized to receive interferon-alpha 2b (3 million units three times a week) plus thymosin-alpha l (900 microg/m2 body surface area) and 19 received interferon-alpha 2b alone at the same dose. Patients were treated for 6 months and followed up for another 6 months. Biochemical (alanine aminotransferase values) and virological (hepatitis C virus-RNA) responses to treatment were determined. Combination treatment showed significantly higher efficacy than monotherapy in achieving virological end-of-treatment response (P = 0.03). At 6-month follow up, the sustained biochemical and virological response was not different between the two groups. Our results indicate that the immune modulator TA1 may enhance the end-of-treatment response in naive patients with chronic hepatitis C. Higher doses and/ore more prolonged courses as well as the association with new interferon formulation such as pegylated interferons could improve the sustained response rates to this treatment.

Thymosin alpha(1) in combination with cytokines and chemotherapy for the treatment of cancer

Multiple therapeutic approaches have been tested in different experimental tumour models and in human cancers. Most part of them are based on the hypothesis that the inhibition of tumour growth requires a strong immune response in which a main role is played by CTLs. It is known, however, that an efficient CTL response requires expression of tumour antigens, MHC class I surface molecules presentation, expression of different co-stimulatory molecules and a sustained generation and proliferation of specific cytotoxic CD8+ cells with an efficient CD4+ cooperation. In this context, our group has extensively explored a protocol of combined therapy consisting of the use of chemotherapeutic agents associated with thymosin alpha 1 (Talpha 1) and different cytokines, whose efficacy has been demonstrated in experimental models as well as in human cancers. In this manuscript, the main data supporting a pivotal role of Talpha 1 in such combination protocols are reviewed. In particular, a special mention of the molecular mechanisms underlying the effects of Talpha 1 on immune effector cells as well as on target tumour cells is provided. These data contribute to explain the mechanism of action of Talpha 1, when used in combination therapy, for the treatment of cancer and provide new insights in predicting further possible applications of this peptide in other pathological conditions.

In vitro effect of thymosin-alpha1 and interferon-alpha on Th1 and Th2 cytokine synthesis in patients with chronic hepatitis C

Current evidence suggests that increased expression of Th1-associated cytokines is important for immune-mediated eradication of hepatitis C infection, while an increase in Th2-associated cytokines is associated with persistence of infection. In this study we evaluated the effects of thymosin-alpha1 (TA1), a naturally occurring thymic peptide, and interferon-alpha (IFN-alpha) on cytokine production in peripheral blood mononuclear cells from untreated patients with chronic hepatitis C. We examined the effect of incubation with TA1, IFN-alpha, or both, on production of Th1-associated cytokines (IL-2, IFN-gamma), Th2-associated cytokines (IL-4, IL-10), and synthesis of the antiviral protein 2',5'-oligoadenylate synthetase. TA1 treatment induced a significant increase in production of IL-2 and 2',5'-oligoadenylate synthetase. Smaller increases were also seen after treatment with IFN-alpha, while incubation with TA1 and IFN-alpha together led to an additive or synergistic effect. Incubation with TA1 resulted in a decrease in IL-4 and IL-10, whereas IFN-alpha increased these cytokines. The addition of TA1 to IFN-alpha significantly reversed this IFN-alpha-induced increase. Hence, TA1 treatment could benefit patients with hepatitis C infection by increasing the Th1-type response, fundamental for sustained clearance of hepatitis C; and by decreasing the Th2-type response, associated with persistence of viraemia.

Thymosin alpha 1 in the treatment of cancer: from basic research to clinical application

Many studies have explored the effects of immunotherapy, alone or in combination with conventional therapies, on both experimental and human cancers. Evidence has been provided that combined treatments with thymosin alpha 1 (T alpha 1) and low doses of interferon (IFN) or interleukin (IL)-2 are highly effective in restoring several immune responses depressed by tumor growth and/or cytostatic drugs. In addition, when combined with specific chemotherapy, they are able to increase the anti-tumor effect of chemotherapy while markedly reducing the general toxicity of the treatment. The advantages of using this combined chemo-immunotherapeutic approach in experimental and human cancers are reviewed in this issue.

Combination therapy with BRMs in cancer and infectious diseases

In recent years many studies have stressed the importance of using biological response modifiers (BRMs) in the treatment of different conditions of immune-impairment correlated with ageing, cancer and infectious diseases. In particular, the use of different BRMs in conjunction with conventional therapies has been extensively explored. Our studies have demonstrated that treatment with Thymosin alpha-1 and low doses of IFN or IL-2 exert powerful biological effects both in vitro and in vivo. They are highly effective in restoring cytotoxic activities in immunosuppression induced by tumors and/or cytostatic drugs. In addition, when combined with specific chemotherapy, they are able to induce a dramatic inhibition of tumor growth in both experimental models and in humans. Immunotherapeutic treatment also has an application in controlling infectious diseases, especially those occurring in the immuno-compromised host. The advantage of using the combined immunotherapy treatment with antiviral drugs has been recently demonstrated by our group both in a murine experimental influenza model and in patients infected with HBV, HCV and HIV.

Effects of thymosin alpha1 on the development of amoeboid microglial cells in the corpus callosum of neonatal BALB/c and athymic mice

The present study investigated the effects of intraperitoneal injections of thymosin alpha1 on the supraventricular amoeboid microglial cells (SAMC) in the newborn athymic and normal BALB/c mice. The microglial cells labelled by the lectin GSA I-B4 and the antibody Mac-1 showed a 27% reduction in number in the athymic mice receiving thymosin alpha1 injections compared with those receiving vehicle injections, and a 37% reduction in BALB/c mice receiving thymosin alpha1 injections compared with those receiving vehicle injections. Some of the SAMC in both BALB/c and athymic mice receiving thymosin alpha1 injections became ramified, while the remainder still exhibited their normal amoeboid appearance with few filopodial processes. Ultrastructurally, the lectin reaction product was confined to the plasma membrane and some cytoplasmic vacuoles of labelled SAMC. In both BALB/c and athymic mice, some labelled microglial cells became slender or elongated after thymosin alpha1 injections. Also their cytoplasm was reduced and contained fewer organelles. Radioimmunoassay of the plasma of thymosin alpha1 and vehicle-injected mice showed that there was a significant increase in the cortisol level in BALB/c (P < 0.01) and athymic (P < 0.001) mice 5 days after thymosin alpha1 injections, compared with that of the control mice. The results point to a strong correlation between the reduction of SAMC and the increased level of plasma cortisol. Supporting this is the fact that cortisol is known to suppress the production of monocytes considered to be the precursors of amoeboid microglia.

Thymosin alpha 1 interacts with the VIP receptor-effector system in rat and mouse immunocompetent cells

Thymic peptide thymosin alpha 1 (10(-11) to 10(-6) M) is shown to interact with the VIP receptor-effector system in rat and mouse peritoneal macrophages, and both rat peripheral blood lymphocytes and spleen lymphocytes. In all models, thymosin alpha 1 inhibits 125I-VIP binding with a potency that is in a range 1000-1700 times lower than that of the native VIP. Interaction of thymosin alpha 1 with VIP receptors is compared with that of some structurally VIP-related peptides such as helodermin, PHI, secretin, and glucagon. The order of potency in inhibiting 125I-VIP binding was VIP > helodermin > PHI > secretin > thymosin alpha 1. Thymosin alpha 1 (10(-10) to 10(-6) M) was weak in stimulating adenylyl cyclase activity. Its efficacy is in a range 900-1800 times lower than that of native VIP in all cell types studied. The analysis of the sequence of both complete and N-terminal portion of thymosin alpha 1 reveals close structural and physicochemical similarities with the members of the so-called VIP family of polypeptides. Taken together, experimental data support that thymosin alpha 1 must be included like the lowest partial agonist of the VIP family of polypeptides and it is a VIP receptor antagonist with weak intrinsic activity.

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.

Diminished thymosin alpha-1 levels in persons exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

There is evidence from animal studies that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) impairs immune responses, with the thymus being a principal target organ. The purpose of this study was to evaluate thymic function, through measurement of thymic hormone levels, in persons exposed to TCDD. We examined thymosin alpha-1 (Thya-1) levels in sera from a group of 94 persons who were presumed to be exposed to TCDD from living, working, or recreating in a contaminated residential area. We compared these results, along with results from in vitro and in vivo tests of immune function, with those from a group of 105 unexposed persons who were similar with regard to age, sex, and race. The exposed group had a significantly lower mean Thya-1 serum level (977.3 +/- 304.1 pg/ml vs. 1148.7 +/- 482.1 pg/ml, p less than .01 by t-test). We also found a statistically significant trend of decreasing Thya-1 levels with increasing number of years of residence in the TCDD-contaminated area. However, Thya-1 levels were not associated with other measures of immune function in the TCDD-exposed group. Thus, while the principal findings suggest that long-term TCDD exposure may be associated with diminished secretion of Thya-1, the lack of an association with an increased prevalence of clinically diagnosed immune suppression in these TCDD-exposed persons makes the biologic significance of the findings unclear. Further studies are needed to more fully evaluate possible long-term TCDD-induced effects on the thymus and human immune function.

Localization of immunoreactive thymosin alpha 1 in astrocytes of normal human brain

We employed an immunocytochemical method to examine human brain for the presence of immunoreactive thymosin alpha 1 (T alpha 1), a peptide derivative of thymic tissue, using a well-characterized antiserum. For cell identification, serial sections were stained with antisera to thymosin beta 4(T beta 4), another thymic peptide that identifies oligodendrocytes, and with anti-glial fibrillary acidic protein (GFAP) antiserum that stains astrocytes in a double-staining technique using avidin-biotinylated horseradish peroxidase or avidin-biotinylated alkaline phosphatase complex. Antiserum to T alpha 1 stained the cell body, but not the processes, of GFAP-positive astrocytes, suggesting that T alpha 1 is a common antigen shared between thymus and astrocytes. Because T alpha 1 and its precursor molecule play a role in cell proliferation and immunomodulation, our findings could explain the role of astrocytes in certain central nervous system diseases.

Production of human B and T cell growth factors is enhanced by thymic hormones

The thymic preparations thymosin fraction 5 (TF5) and synthetic thymosin alpha 1 (T alpha 1) were examined for their ability to enhance growth factor production by human peripheral blood mononuclear cells (PBMC). The results showed that both TF5 and T alpha 1 were capable of enhancing the production of a B cell growth factor (BCGF-12kD) and T cell growth factor (TCGF; IL-2). Enhancement by T alpha 1 could be obtained at 100-200-fold lower concentrations than that seen with TF5. In contrast, no enhancement of growth factor production was obtained with control preparations of non-thymic tissue extracts at any concentrations used. It was observed that stimulation of BCGF-12kD and IL-2 was most significantly obtained when the PBMC were activated with lectin. Furthermore, no direct effect of thymic hormones on test B and T cells was observed. These observations provide the first direct evidence that production of B cell growth factors can be enhanced by thymic hormones. In addition, these studies suggest that thymic hormones may regulate B cell responses by acting on mature activated T lymphocytes.

Defective in vitro gamma interferon production and elevated serum immunoreactive thymosin beta 4 levels in patients with inflammatory bowel disease

Gamma interferon (IFN-gamma) production by peripheral blood mononuclear cells (PBM) was measured in 21 patients with Crohn's disease, in 15 patients with ulcerative colitis, in 12 patients with non-IBD gastrointestinal disease (disease control), and in 28 healthy controls. T-cell subset proportions and serum levels of thymosin alpha 1 and thymosin beta 4, two hormonelike thymic peptides, were also determined. No differences were seen in T-cell subset proportions in patients with Crohn's disease or ulcerative colitis when compared to healthy controls or to the disease-control group. In vitro IFN-gamma production was markedly decreased in Crohn's disease and in untreated, but not treated, patients with ulcerative colitis. Preincubation of PBM prior to the addition of inducer mitogen resulted in enhanced IFN-gamma production in patients with Crohn's disease or ulcerative colitis which significantly exceeded that seen either in healthy controls or in the disease-control group. Serum thymosin alpha 1 levels were comparable in all study groups; however, serum thymosin beta 4 concentrations were significantly higher in all patient groups than in the healthy controls. These results confirm a defective in vitro IFN-gamma production in patients with IBD which is apparently independent of endocrine thymus regulation.

Improved ELISA to measure thymosin alpha 1: comparison of whole and absorbed antisera

An improved microELISA to measure thymosin alpha 1 (T alpha 1) is described which uses a rabbit antibody against T alpha 1 that has been absorbed with a synthetic C-14 fragment of T alpha 1. This assay is compared to the previous assay which used the whole antisera. The antibodies to T alpha 1 are preincubated with the standard or human sera overnight at 4 degrees C, then incubated for an additional 24 h in microtiter plates coated with T alpha 1. Using the whole antiserum, the average T alpha 1 level was 2480 +/- 1110 (mean +/- S.D.) pg/ml by ELISA and 2360 +/- 870 pg/ml by radioimmunoassay (RIA) in eight different samples of human cord sera. Using the N-specific absorbed antiserum the mean T alpha 1 level was 11,800 +/- 4800 pg/ml by ELISA and 10,600 +/- 5200 pg/ml by RIA. Recoveries of exogenously added T alpha 1 are complete (109 +/- 25% for whole and 108 +/- 15% for absorbed antisera). The absorbed antiserum has an increased affinity for the amino acid terminal region of T alpha 1 and the T alpha 1 values by use of absorbed antisera are significantly higher (3-5 x) than those measured using the whole antisera. Thus, the absorbed antisera produces an ELISA which is more sensitive and specific for serum thymosin alpha 1.

Substance P enhances interferon-gamma production by human peripheral blood mononuclear cells

Substance P (SP), a neuropeptide widely distributed in the organism, has been shown to stimulate lymphocyte proliferation and immunoglobulin synthesis. However, the effect of SP on specific lymphokines is unknown. Therefore we investigated the influence of SP on mitogen-induced interferon-gamma (IFN-gamma) production in vitro. Peripheral blood mononuclear cells (PBMC) of healthy donors were isolated by density gradient centrifugation and cultured in supplemented RPMI 1640 medium with phytohemagglutinin (PHA) or pokeweed mitogen (PWM), 0.125 and 0.25 mg/liter each, and varying concentrations of SP (10(-12) to 10(-6) M). After 24 and 48 h, IFN-gamma was measured in the supernatant using radioimmunoassay. Results were expressed as percent change of controls. SP alone had no relevant IFN-gamma inducing properties. It enhanced the IFN-gamma production of PWM-stimulated cells significantly up to 18%. The maximal effect was observed at 10(-8) M. PHA-stimulated cells also increased their IFN-gamma production after addition of SP. However, due to great interindividual variations this effect did not attain statistical significance. Stimulation of IFN-gamma production by SP might be of physiological importance, since the effect was seen at concentrations comparable to those found in the body. Our data lend further support to the immunoregulatory functions of SP.

A radioimmunoassay for thymosin alpha-1

A new radioimmunoassay (RIA) is described for the quantitation of thymosin alpha-1 (alpha-1). The assay employs an antiserum specific for the COOH-terminal half segment 15-28 of alpha-1, synthetic alpha-1-(15-28) as the hormone standard, and a radioiodinated N alpha-acetyltryrosyl-alpha-1-(15-28) as the tracer. Since alpha-1-(1-28) lacks a phenolic ring for direct radioiodination, the N alpha-acetyltyrosyl-alpha-1-(15-28) was synthesized by the solid-phase method. The peptide bears a Tyr in place of Lys in position 14 of the natural peptide. It showed full alpha-1-(15-28) immunoreactivity and its radioiodinated derivative served as tracer in the RIA. An anti-alpha-1-(15-28) antiserum was raised in a rabbit and was shown to recognize alpha-1-(15-28) or its tyrosyl analogue, and the peptide, alpha-1-(1-28). But it did not recognize other thymic hormones or the biologically active segment 32-36 of thymopoietin, or structurally unrelated peptides. It could also detect natural alpha-1 cross-reacting material in the cytoplasm of cultured human thymic epithelial cells as measured by indirect immunofluorescence. In the RIA, as little as 9 pg of alpha-1-(15-28) equivalents in a 50 microliter sample could be detected. In addition, alpha-1-(1-28)-like immunoreactivity was quantitated in 6 human thymus homogenates and ranged from 0.5 to 4.5 ng/mg of protein.

MicroELISA method for measurement of human serum thymosin alpha 1

A microELISA for the estimation of human serum thymosin alpha 1 is described. In this assay, antibody to thymosin alpha 1 is pre-incubated with the standard or serum at 4 degrees C. Unbound antibody in the liquid-phase then binds with solid-phase thymosin alpha 1. The method is sufficiently sensitive for measuring serum levels of thymosin alpha 1 and highly reproducible. The serum levels measured with the microELISA are comparable to serum levels of thymosin alpha 1 determined by the previously described radioimmunoassay for thymosin alpha 1.

Mechanism of action of thymosin. II. Effects of aspirin and thymosin on enhancement of IL-2 production

Recent studies have shown that thymosin fraction 5 (TF5) enhances production of interleukin-2 (IL-2) by phytohemagglutinin (PHA)-stimulated normal human peripheral blood mononuclear leukocytes (PBL). In this study we sought to determine whether this effect of TF5 might be mediated via the cyclooxygenase or lipoxygenase pathways. Our studies demonstrate that aspirin, an inhibitor of the cyclooxygenase pathway, given in vivo, or added to cultures in vitro, results in two-fold increased IL-2 production by PHA-stimulated PBL. This increase is comparable to that seen when PBL are cultured in vitro with TF5. When aspirin and TF5 are added simultaneously to PBL in the presence of PHA, an additive response is seen. An inhibitor of the lipoxygenase pathway, 15-hydroxyeicosatetraenoic acid, did not significantly change IL-2 production by PBL or influence the enhancement by TF5. Augmentation of IL-2 production by aspirin and/or TF5 was prevented by monocyte depletion of the PBL population. These results are interpreted as demonstrating (a) that TF5 and aspirin augment, by distinct mechanisms, IL-2 production by normal human PBL, (b) that the effects of both of these agents are mediated directly or indirectly via a monocyte population and (c) that aspirin, in addition to its analgesic and anti-inflammatory properties, may act as a modulator of immunological responsiveness, either alone or in combination with other biological response modifiers such as thymosin.

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.

Thymosin increases production of T-cell growth factor by normal human peripheral blood lymphocytes

The in vitro incubation of phytohemagglutinin-stimulated peripheral blood lymphocytes with thymosin results in a marked and reproducible increase in production of T-cell growth factor, which is dose dependent and most pronounced in the first 24 hr of culture. Incubation of lymphocytes with thymosin alone failed to induce any production of T-cell growth factor. The biological activity of thymosin fraction 5 cannot be attributed to the activity of thymosin alpha 1, one of the well-characterized peptide components of fraction 5. These data provide the basis for (i) a potential mechanism for the in vivo immunorestorative effects of thymosin in primary and secondary immunodeficiencies and (ii) identification of an additional, but as yet undefined, immunoregulatory component of thymosin fraction 5.

Modulation of endogenous prostaglandins by thymosin-alpha 1 in lymphocytes

The effects of thymosin-alpha 1 on the stimulation of specific release of prostaglandin E2 (PGE2) from splenic lymphocytes and thymocytes were studied. Experiments were also performed to study in parallel the absolute levels of thymosin-alpha 1 in the blood and the induction of serum FTS activity and of azathioprine sensitivity of spleen cells from adult thymectomized (ATx) mice. A significant difference in the release of PGE2 between normal splenocytes and splenocytes from ATx mice was observed. Thymosin-alpha 1 at certain concentrations was able to stimulate PGE2 release from lymphocytes of ATx mice while inhibiting release in lymphocytes of normal mice. Also, thymocytes were stimulated to release PGE2 after incubation with alpha 1 in a manner similar to that seen in spleen cells of ATx mice. Approximately the same concentrations of alpha 1 was found to also correct the low azathioprine sensitivity of splenocytes from ATx mice. Determinations of FTS-like activity in the blood and the pharmacokinetics of alpha 1 after administration of this synthetic molecule show a clear dissociation. A maximum peak of alpha 1 activity was obtained after 1 hr, while maximal FTS-like activity was observed after 24 hr. The inhibition of the induction by alpha 1 of FTS-like activity and of Thy 1.2 antigen by indomethacin suggests that the action of alpha 1 requires prostaglandin biosynthesis.

Enhancement of murine thymocyte cytotoxic T cell responses by thymosin

Incubation of murine thymocytes with thymosin Fraction 5 (F5) results in a twofold enhancement of the cytotoxic T lymphocyte response (CTL). The assay exhibits requirements for optimal concentrations of thymosin (100 micrograms/ml) and optimal responder/stimulator ratios. Enhancement of CTL activity can be demonstrated in several responder/stimulator strain combinations. The data indicate that thymosin F5 acts via the responder thymocyte population rather than the stimulator cells, since comparable effects were obtained using nude spleen stimulator cells devoid of mature T cells. This system provides a useful bioassay for identifying the component peptides of thymosin F5 which promote thymocyte differentiation and/or maturation and for elucidating the mechanisms of action of the biologically active thymosin peptides.

Gamma interferon production by different populations of human splenic lymphocytes

The treatment of cultures of human splenic lymphocytes with Staphylococcal enterotoxin A (SEA) resulted in the production of human gamma interferon (HuIFN-gamma). Separation of lymphocyte populations to give preparations enriched in T or B lymphocytes after removal of macrophages demonstrated that maximum IFN titers were detected when T lymphocytes were incubated with macrophages for a period of three days. The levels of IFN-gamma varied from donor to donor but the kinetics of induction were quite similar in all cases. Concentrations of 0.5-1.0 microgram/ml SEA gave optimal induction of IFN and the addition of thymosin alpha-1 at 10 micrograms/ml to the culture medium enhanced IFN-gamma production.