Chemical characterization of thymosin beta 4

Modulation of cellular gene expression of HIV type 1 infection as determined by subtractive hybridization cloning: downregulation of thymosin beta 4 in vitro and in vivo

Chronic infection with HIV-1 has profound effects on host cell growth and function. We used subtractive hybridization cloning to identify genes whose expression is modulated by HIV-1 infection in the T leukemia cell line CEM. The gene encoding thymosin beta 4, a ubiquitous polypeptide associated with hematopoietic differentiation, showed two- to threefold reduced transcription in HIV-1-infected CEM cells and other HIV-1-infected T cells and macrophages in vitro. Solid-phase radioimmunoassay revealed about a threefold decrease in the level of thymosin beta 4 protein in lysates of infected cells. Northern blot analysis of RNA samples from lymphocytes of five AIDS patients reveals an up to fivefold reduction in the level of thymosin beta 4 mRNA. These results indicate that HIV-1 infection may directly influence the expression of certain physiologically important proteins.

Effects of thymosin beta 4 and thymosin beta 10 on actin structures in living cells

The beta-thymosins are a family of small proteins originally isolated from the thymus. Recently, two of the major mammalian isoforms, thymosin beta 4 (T beta 4) and thymosin beta 10 (T beta 10), are identified as significant actin monomer sequestering proteins which may be involved in regulating actin filament assembly. To study the cellular function of beta-thymosins, we have used isoform-specific antibodies to determine their concentration and intracellular distribution, and examined the effects of inducing overexpression of T beta 4 and T beta 10 on actin filament structures. Immunofluorescence labeling of peritoneal macrophages showed that both beta-thymosins are uniformly distributed within the cytoplasm. cDNA-mediated overexpression of beta-thymosins in CV1 fibroblasts induced extensive loss of phalloidin-stained actin stress fibers. Stress fibers in the cell center were more susceptible than those at the periphery. There was a decrease in the number of focal adhesions, as evidenced by a decrease in discrete vinculin staining and an increase in diffuse vinculin fluorescence. The majority of the transfected cells had normal shape in spite of extensive loss of actin filaments. Occasionally, cells overexpressing beta-thymosin were observed to divide. In these cells, beta-thymosin was excluded from the midbody which contains an actin filament-rich contractile ring. Our results indicate that T beta 4 and T beta 10 are functionally very similar and both are effective regulators of a large subset of actin filaments in living cells.

Thymosin stimulates interleukin-6 production from rat spleen cells in vitro

Thymosin fraction 5 (TF5) is a partially purified preparation of bovine thymus that affects the differentiation and function of T-cells in vitro. Interleukin-6 (IL-6) is a pleiotropic cytokine that induces terminal maturation of B-cells and T-cell activation and differentiation. Although TF5 had previously been shown to stimulate the production of a number of lymphokines, its effects on IL-6 were not known. In this study we determined the effect of TF5 on IL-6 production from rat spleen cells in vitro. TF5 (100 micrograms/ml) stimulated IL-6 production from splenocytes (0.75-3.0 x 10(5) cells/well) in the presence of 0.008-0.2 micrograms/well of the T-cell mitogen concanavalin-A (con-A) by 10-20 fold during a 72 h incubation period. Dose-response studies demonstrated that 10 micrograms/ml of TF5 was the lowest concentration capable of enhancing IL-6 production. The ability of TF5 to stimulate IL-6 production in the presence of con-A could be demonstrated within 24 h of incubation; longer incubation periods (48-72 h) correlated with further enhancements of IL-6 production. Partial purification of the IL-6-inducing activity from TF5 resulted in three subfractions possessing activity in the presence of con-A (MB2, MB3, MB7) and one in the absence of con-A (MB2). The previously characterized thymosin peptides T alpha 1 and T beta 4 had no effect on IL-6 production in the absence or presence of mitogen. This study reports a new biological activity for TF5 and suggests that a novel constituent of TF5 may enhance the production of IL-6 from spleen cells.

Thymosin beta 4 synergizes with human granulocyte-macrophage colony-stimulating factor in maintaining bone marrow proliferation

Recent evidence supports a role for thymosin beta 4 (T beta 4) in the inhibition of murine hematopoietic stem cell proliferation. This supposition results from studies in which the N-terminal tetrapeptide derived from native T beta 4 was administered to mice and appeared to prevent CFU-S recruitment into DNA synthesis. The importance of this observation was the concomitant ability of the tetrapeptide to prevent cytosine arabinoside (ara-C) toxicity in mice given LD50 doses of this drug. In the present study, we have extended these observations by demonstrating that whole synthetic T beta 4 is more effective than the N-terminal tetrapeptide in protecting mice from the toxicity of ara-C. This observation supports the hypothesis that T beta 4 is the biologically important parent molecule for this activity. To determine if inhibition of cell cycle progression also occurs in committed human bone marrow progenitors treated with T beta 4, we have investigated the effects of synthetic T beta 4 on proliferating and unstimulated enriched human bone marrow. In short-term liquid cultures studied sequentially over 1-7 days, T beta 4 failed to inhibit cell proliferation, but maintained the proliferative effect of granulocyte-macrophage colony stimulating factor (GM-CSF) on days following maximum stimulation (days 5-7). No effect was noted before the fifth day in culture, nor did T beta 4 exert any demonstrable effect in the absence of added GM-CSF. Any observable effect of T beta 4 required that it be present in the cultures on or before day 3 of GM-CSF stimulation. These results suggest that an additional effect of T beta 4 is the stimulation of a subpopulation of committed human bone marrow precursor cells to become more sensitive to the growth-promoting activity of GM-CSF, thereby enhancing myelopoiesis. It is of interest that the N-terminal peptide of T beta 4 is a shared sequence with tumor necrosis factor alpha, which is also known to have a similar stimulatory capacity. We, therefore, postulate that the growth enhancement noted in short-term cultures is mediated by the region containing these shared sequences.

Actin-sequestering ability of thymosin beta 4, thymosin beta 4 fragments, and thymosin beta 4-like peptides as assessed by the DNase I inhibition assay

Thymosin beta 4 containing 43 amino-acid residues belongs to a family of highly homologous peptides present at high concentrations in various species, cells, and tissues. Safer et al. [J. Biol. Chem. 266, 4029-4032 (1991)] have shown that thymosin beta 4 is an actin-sequestering peptide. Because DNase I is inhibited by G-actin and not by F-actin we employed this enzymatic assay to determine the actin sequestering properties of 4 other thymosin beta 4-like peptides and fragments of thymosin beta 4 generated by enzymatic digestions. Thymosin beta 4 sequesters G-actin at a 1 to 1 ratio an thereby inhibits its polymerisation to F-actin in high salt solution. The oxidation of the single methionine residue at position 6 does not abolish its actin-sequestering properties. However neither thymosin beta 4 24-43 nor thymosin beta 4 13-43 inhibit the polymerisation of G-actin. We conclude from this that some structural features in the amino-acid sequence of thymosin beta 4 before position 13 are obligatory for its biological function. Oxidized thymosin beta 4 (beta 4-sulfoxide) as well as four other thymosin beta 4-like peptides were shown to be actin-sequestering peptides like thymosin beta 4.

Expression of thymosin beta-4 and related genes in developing human brain

The retinoic acid-responsive thymosin beta-10 gene is known to be developmentally regulated in the human brain. We now report the novel finding that thymosin beta-4, a structurally related 5-kDa actin-sequestering protein, is also subject to a similar but not identical pattern of expression during normal human neuroembryogenesis. However, while thymosin beta-10 mRNA was undetectable (by northern blot analysis) in adult human brain, levels of thymosin beta-4 mRNA, although greatly reduced, were still present. Moreover, a novel thymosin beta-10-like gene was also found to exhibit a unique stage-specific expression during early human neural development. These experiments, together with previous findings, indicate that the products of the two thymosin genes, possibly in association with cytoskeletal elements, may play different roles during early neuroembryogenesis and neural maturation.

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.

Primary structure of thymosin beta 12, a new member of the beta-thymosin family isolated from perch liver

A new polypeptide termed thymosin beta 12 has been isolated from perch liver and its primary structure elucidated. This polypeptide contains 43 amino acid residues with a molecular weight of 4822 Da. The content of thymosin beta 12 from perch liver has been determined as 43 micrograms/g of tissue. The amino-terminal end of this polypeptide is blocked by an acetyl group as deciphered by fast-atom bombardment mass spectrometric analysis. Sequence analysis reveals that thymosin beta 12 is 79% homologous to thymosin beta 4, an immunomodulator which was originally isolated from calf thymus. Thymosin beta 12 also shows 84% sequence homology to thymosin beta 11, a beta 4 analog which replaces beta 4 in two species of bony fish, oscar and rainbow trout. The evolutionary implication of such results will be discussed. The isolation of a new beta 4-related peptide from perch liver which differs from beta 11 indicates that beta-thymosin peptides are widely distributed in lower vertebrate classes.

Formation of acetyl-Ser-Asp-Lys-Pro, a new regulator of the hematopoietic system, through enzymatic processing of thymosin beta 4

The demonstration that AcSDKP, a new regulator of the hematopoietic system, is formed in the bone marrow by a one-step enzymatic maturation processing of thymosin beta 4 (T beta 4) is presented. AcSDKP and T beta 4 were both detected in bone marrow cells (BMC). Incubation of [3H]T beta 4 with either intact or lysed BMC led to the formation of [3H]AcSDKP, whereas the labeled tetrapeptide was not degraded under these conditions. Model enzymatic degradation of T beta 4 carried out with bacterial enzymes suggests that a mammalian endoproteinase Asp-N might be involved in the formation of AcSDKP through the specific cleavage of the Pro4-Asp5 peptidic bond of T beta 4. In contrast, alpha-prolyl-endopeptidase was ineffective in carrying out a similar processing.

Human thymosin-beta 4/6-26 gene is part of a multigene family composed of seven members located on seven different chromosomes

We have isolated a cDNA encoding the human interferon-inducible gene 6-26, by screening a cDNA library with an oligodeoxynucleotide probe. Its sequence was found to be identical to that of the human thymosin-beta 4 cDNA, which encodes a protein present in most cell types, but whose function is not clear at present. By hybridization of the thymosin-beta 4/6-26 cDNA to the DNA of a panel of human-rodent somatic cell hybrids, we found that at least seven genes homologous to this cDNA are present in the human genome. We localized these genes, some of which might be pseudogenes, to seven distinct chromosomes, namely, chromosomes 1, 2, 4, 9, 11, 20, and X.

Structure and immunological properties of thymosin beta 9 Met, a new analog of thymosin beta 4 isolated from porcine thymus

During the course for the studies of thymosin beta 4 and prothymosin alpha from porcine thymus, a new analog of thymosin beta 4 has been identified. This peptide consists of 41 amino acid residues. The amino terminus is blocked by an acetyl group as revealed by fast atom bombardment mass spectrometric analysis. Amino acid sequence studies disclosed that this peptide is identical to bovine thymosin beta 9 except that leucine at position 6 in beta 9 is substituted by methionine. Thus, this new peptide has been termed thymosin beta 9 Met. The recoveries of beta 9 Met, beta 4, and prothymosin alpha in porcine tissues have been determined (in micrograms/g tissue) as follows: thymus (43, 85, 133); spleen (68, 203, 37); liver (10, 31, 27); heart (1.5, 10, 0); kidney (5, 51, 37); brain (0.8, 31, 5). Biologically, thymosin beta 9 Met was found to be more active than beta 4 in enhancing gamma-interferon production in cord blood lymphocytes. However, beta 4 appeared to stimulate higher amounts of interleukin 2 and tumor necrotic factor. The significance for the coexistence of two homologous peptides with similar functions in the thymus and a number of other organs is not clear, and deserves further investigation.

Depression of prothymosin alpha production in murine thymus correlates with staphylococcal enterotoxin-B-induced immunosuppression [corrected]

Prothymosin alpha [corrected] (ProT alpha) and thymosin beta 4 [corrected] (T beta 4) were isolated from murine thymus and characterized by microsequence analysis. Murine T beta 4 has an identical sequence to bovine T beta 4, whereas murine ProT alpha is highly homologous to rat Pro T alpha. Murine Pro T alpha differs from rat Pro T alpha at two positions, Glu100 and Asp108 of the rat sequence are substituted by aspartic and glutamic acid, respectively, in murine Pro T alpha. The amount of Pro T alpha in murine thymus was found to be reduced after in vivo treatment with staphylococcal enterotoxin B [corrected] (SEB), a superantigen which stimulates T cells bearing specific V beta receptors. Results from the anti-SRBC (sheep erythrocyte) plaque-forming cell assay showed that the antibody response of the spleen cells from these animals was also suppressed. On the other hand, the amount of T beta 4 was not changed significantly. Our studies suggest that the suppression of SEB on antibody response correlates with the depression of Pro T alpha production in the thymus.

Thymosins: both nuclear and cytoplasmic proteins

A simple procedure based on perchloric acid extraction has been developed for the preparation and purification of bovine prothymosin alpha and thymosins beta 4 and beta 9 in high yields. Spectroscopic observations show these proteins to be non-folding at neural pH. The cellular locations of human prothymosin alpha, rat parathymosin and calf thymosin beta 4, all so-called 'thymic hormones', have been studied by injection into the cytoplasm of Xenopus oocytes, followed by separate monitoring of nuclear and cytoplasmic concentrations. It is shown that human prothymosin alpha and rat parathymosin both migrate to the nucleus whilst thymosin beta 4 remains in the cytoplasm. The peptide (1-88) of calf prothymosin alpha is shown not to accumulate in the Xenopus nucleus, demonstrating that the C-terminal 21 residues, which include a KKQK sequence, are required for nuclear migration. The present data, in association with existing evidence of wide tissue distribution and the lack of signal peptides, indicate that these proteins do not behave as hormones in the usual sense of the word. It is suggested that thymosin beta 4 should be grouped separately from the pro- and parathymosins.

Changes in circulating levels of neuroendocrine and thymic hormones during aging in rats: a correlation study

It is well established that during early life the thymus gland and the neuroendocrine system influence each other's maturation. Furthermore, there is a growing body of evidence indicating that the immune and neuroendocrine systems also function as a bidirectional network during adult life. In order to assess possible changes in the thymic-neuroendocrine network during aging, we undertook to measure and correlate the circulating levels of several neuroendocrine and thymic hormones in young (3 month) and old (26 month) male Sprague-Dawley rats. Sequential plasma samples were obtained from chronically cannulated, nonstressed animals every 30 min for 5 h. Two days later rats were killed between 11:30 a.m. and 1:30 p.m. and trunk serum was obtained. All hormones were measured by radioimmunoassay. Growth hormone (GH), prolactin (PRL), thyrotropin (TSH) and corticosterone were measured in plasma, whereas thyroxine (T4), triiodothyronine (T3), thymosin alpha 1 (T alpha 1) and thymosin beta 4 (T beta 4) were determined in trunk serum. The circulating levels of T3, PRL, corticosterone and T beta 4 did not show significant differences between young and old rats, whereas GH, T4, T alpha 1, and thymus weight showed a significant age-related reduction. The anterior pituitary (AP) weight and plasma TSH were significantly higher in old than in young rats. Three pairs of parameters showed highly significant levels of linear correlation: AP weight vs. T alpha 1; thymus weight vs. T4 and T alpha 1 vs. T4 (p less than 0.01, p less than 0.001 and p less than 0.001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Thymosins alpha 1 and beta 4 potentiate the antigen-presenting capacity of macrophages

The immunomodulatory effects of thymosins on the Ag-presenting capacity of macrophages were investigated. Using an in vitro antigen (Ag)-specific macrophage-dependent T-cell proliferation system, we found that both thymosin alpha 1 (T alpha 1) and thymosin beta 4 (T beta 4) augment the Ag-presenting capacity of macrophages. Macrophage monolayers were pulsed with keyhole limpet hemocyanin (KLH) in the absence or presence of thymosins, washed and overlaid with spleen cells. Splenocytes were collected, mitomycin C-treated and injected into syngeneic mice. Draining lymph node cells were tested for Ag-specific response by measuring proliferation, interleukin 2 (IL-2) secretion and expression of IL-2 receptors (IL-2R) on their cell surface. We found that the presence of thymosins during the pulsing of macrophages with KLH led to significantly enhanced lymph node cell proliferation responses to KLH was correlated to increased IL-2 production and IL-2R expression. The concentrations of T alpha 1 and T beta 4 required for amplification were 10(-8) to 10(-10) M, well within the physiological range of activity of most peptide hormones. The observed enhancement of IL-2 secretion was not accompanied by interleukin 4 (IL-4) production. This study is the first to demonstrate that thymic hormones have the ability to increase the efficiency of antigen presentation by macrophages. The results suggest that an initial step in the regulation of the immune function by T alpha 1 and T beta 4 may involve activation of the macrophages at the time of antigen presentation.

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.

A comparative study on the immunological effects of bovine and porcine thymic extracts: induction of lymphoproliferative response and enhancement of interleukin-2, gamma-interferon and tumor necrotic factor production in vitro on cord blood lymphocytes

Forty samples of cord blood lymphocytes were isolated from 40 normal healthy full-term newborns. The initial 20 samples were used to determine the dose-response curve of three different thymic extracts (TP-1, bovine thymic extract; TG-15-I and TG-15-II, both porcine thymic extracts) and one of renal origin (KG-1) as a control of non-lymphoid organ extract, by measuring the E-rosette T cells. Results showed that E-rosette T cells increased significantly when the thymic extract concentration was increased to 12.5 micrograms/ml. However, there was no statistical difference between TP-1, TG-15-I and TG-15-II in the increase of E-rosette-forming cells. The remaining 20 samples were preincubated with 0, 12.5, 25 or 50 micrograms/ml of thymic extracts. It was observed that the lymphoproliferation, interleukin-2 (IL-2), gamma-interferon (IFN-gamma) and tumor necrotic factor (TNF) production were all significantly increased after thymic extract treatment. No statistical difference between these three thymic preparations in the stimulation of lymphoproliferative response was found. However, among the three thymic extracts, TP-1 appears to induce the highest amounts of IL-2, IFN-gamma and TNF. Of the TG-15-I and TG-15-II, the former stimulates higher IL-2 production whereas the latter enhances IFN-gamma and TNF production. The different immunostimulating effects and potencies that these three thymic extracts showed may reflect not only the species difference but also the difference in preparation procedures. Different components in these thymic extracts may be responsible for different biological activities. Results from these comparative studies may provide useful information in future clinical trials for the treatment of the primary immunodeficiency diseases according to their pathogenesis and may also indicate a possible beneficial effect of the combination of chemotherapy and thymic extracts.

Rapid isolation of thymosin beta 4 from thymosin fraction 5 by preparative high-performance liquid chromatography

We have developed a rapid, efficient, and reproducible two-step method for the purification of thymosin beta 4 (T beta 4) from thymosin fraction 5 (TF5). This purification is based on the use of high-performance preparative/semi-preparative and analytical reversed-phase (Delta-Pak C18) chromatographic columns. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and amino acid compositional analysis have shown that natural, purified T beta 4 is identical to synthetic T beta 4. This procedure can be used to isolate other biologically active peptides from TF5 in sufficient quantity for characterization.

An extract of bovine thymus stimulates human keratinocyte growth in vitro

An extract prepared from newborn calf thymus stimulated proliferation of human keratinocytes cultured from newborn foreskins and from skin biopsies of 26 adult volunteers aged 19 to 70 years. Growth over the 7-day assay period in the basal medium was age-dependent, with newborn cultures achieving a 10-fold increase in cell number over seeding density, old adult cultures barely maintaining their seeding density and young adult cultures intermediate in proliferative capacity. Maximally stimulatory extract concentration was 5-fold higher for newborn than for adult keratinocytes, with adult cultures experiencing toxicity at doses still growth-promoting for newborn cultures. At optimal extract concentration the maximal average increase in cell yield (66.3% for newborn, 53.6% for young adult, and 18.1% for old) indicated decreased mitogen responsiveness or increased inhibitor sensitivity with increasing donor age. Stimulation of cholera toxin-treated cultures was equally high, ranging from 39.4% to 145.9%, suggesting that the extract acts through a cyclic AMP-independent pathway. Thymic extract did not increase colony forming efficiency. Our findings provide further support for the concept of functional interactions between the skin and the immune system, in addition to the recognized morphologic similarities between thymic cells and keratinocytes. Furthermore, these data confirm earlier findings of an inverse relationship between mitogen responsiveness and donor age for cultured cells.

Thymosin fraction 5 (TF5) stimulates secretion of adrenocorticotropic hormone (ACTH) from cultured rat pituitaries

In vivo administration of a partially purified thymic hormone-containing extract of the thymus gland, TF5, causes an increase in serum glucocorticoids. The lack of a direct effect of TF5 on adrenal corticosterone secretion suggests that it is mediated at the level of the pituitary. Cultured rat pituitary monolayers were used to determine if the effect is mediated by stimulation of ACTH secretion from the pituitary. Two lots of TF5, BPP100 and C114080-01, caused a dose dependent secretion of ACTH from cultured pituitary monolayers. There was a synergistic effect when the cells were treated with both TF5 and corticotropin-releasing factor (CRF). Immunoneutralization studies were done in which the cells were treated with TF5 or CRF and an antibody to CRF. The antibody completely blocked CRF induced ACTH release, but had no effect on TF5 stimulated ACTH release, suggesting that the activity is not due to a CRF-like peptide in TF5. A number of peptides isolated from TF5, and certain other peptides produced by the immune system were evaluated for their ability to stimulate ACTH secretion. These included thymosin (TSN) alpha 1, alpha 11, and beta 4, prothymosin alpha (PT alpha, thymopoeitin 5 (TP5), factuer thymique serique (FTS), interferon alpha (INF alpha), INF gamma, interleukin 1 (IL-1), and interleukin 2 (IL-2). None of these factors had any effect on pituitary ACTH secretion. These results demonstrate that some peptide component of TF5 causes an increase in serum corticosteroids by stimulating pituitary ACTH release.

One-step procedure for the determination of thymosin beta 4 in small tissue samples and its separation from other thymosin beta 4-like peptides by high-pressure liquid chromatography

Thymosin beta 4 has been determined by a simple and fast one-step procedure in different tissues of rats. The tissues (1 to 40 mg) were disintegrated and deproteinized by homogenization in perchloric acid. After neutralization by potassium hydroxide the supernatant solution was used for determining thymosin beta 4 by reverse-phase HPLC without further manipulations. Not only does this procedure avoid artificial proteolysis as effectively as extraction of tissues by guanidinium chloride or boiling buffer, but it offers two further advantages. First, no additional steps--as for example desalting--are necessary prior to HPLC and thus the risk of losing thymosin beta 4 is eliminated. Using this procedure thymosin beta 4 is recovered quantitatively. The method is linear over the range 0.04 to 1.13 nmol and thymosin beta 4 is well separated from other thymosin beta 4-like peptides known to be present in mammals; i.e., thymosin beta Ala4, thymosin beta 9, thymosin beta 10, and thymosin beta Arg10. Second, the acid-insoluble pellet of the same extract can be used to determine the DNA content of the sample. Thus it is possible to relate thymosin beta 4 to DNA, which then allows comparing cells of different tissues and cell lines to one another. This procedure is also applicable to small peptides soluble in perchloric acid.

Thymosin beta 4 is a shared antigen between lymphoid cells and oligodendrocytes of normal human brain

In the normal human brain, immunoreactive thymosin beta 4, a well-characterized thymic extract, was demonstrated specifically in the cell bodies and processes of a subset of interfascicular and satellite oligodendrocytes with their stained processes terminating around myelin sheaths. Antisera directed against two other thymic polypeptides, thymosin alpha 1 and alpha 7, did not react. In lymphoid tissues, thymosin beta 4 was present in macrophages, Langerhans' cells of the skin, and the interdigitating cells of the thymus. Thus, a subset of oligodendrocytes shares a common antigen of thymic origin with the reticular-dendritic and phagocytic lymphoid cells--all Ia+ immunocompetent cells that participate in the presentation of antigens to T cells. The subset of thymosin beta 4-positive oligodendrocytes is antigenically distinct and may play a role in the immune surveillance of the central nervous system or the demyelinating processes induced by antigen-presenting activated macrophages.

Biosynthesis rates and content of thymosin beta 4 in cell lines

The content and relative biosynthetic rates of thymosin beta 4 have been determined in 28 different cell lines. The highest content of thymosin beta 4 as well as the highest rate of biosynthesis was observed in Epstein-Barr virus-transformed human B-cell lines. The levels observed in these cells are 1 pg thymosin beta 4 per cell, which is three times higher than that in rat peritoneal macrophages. Thus, these B-cell lines have the highest content of thymosin beta 4 of any cell type yet described. Since all of the Epstein-Barr virus-transformed B-cells described here grow in suspension, it is unlikely that the presence of thymosin beta 4 is related to anchorage in these cells. Thymosin beta 4 is not secreted by viable Epstein-Barr virus-transformed B cells in culture, suggesting some intracellular function of the peptide. These results indicate that these B-cell lines may be suitable for the study of thymosin beta 4 function.

Characteristics of the translation of thymosin alpha 1 precursor mRNA by cell-free wheat germ system. Evidence for the acetylation of thymosin alpha 1 precursor

At the optimal concentrations of Mg2+ and K+ to translate total thymus PolyA+-RNA, the purified thymosin alpha 1 precursor mRNA saturate the protein synthetic activity at lower concentration than the total thymus mRNAs. The polyamine spermidine increases the translation rate of the messenger, which is modulated by magnesium, rather than improve the yield in full-length chains of thymosin alpha 1 precursor. As other eukariotic mRNAs, this messenger presents the "cap" modification at the 5'-end terminal position. The incorporation of [3H]acetate into the translation product of the messenger, shows an evidence for the acetylation of the thymosin alpha 1 precursor during its biosynthesis in vitro.

Immunological aspects of aging: early changes in thymic activity

Age related changes in immune function are preceded by changes in thymic function. One index of thymic function is the ability of the thymus to induce the differentiation of bone marrow pre-T cells into active T cells. Movement of precursors of PHA-responsive T cells into the thymus ceases prior to adolescence in long-lived, autoimmune disease resistant mice as determined by studies utilizing chromosome markers in parabiotic mice. The cause for this age-dependent, cell traffic phenomenon is not known, but it would appear that an extrathymic regulatory mechanism may be operating, since these precursor T cells have the capacity to migrate into the thymus, and even a grafted, involuting thymus is capable of accepting precursor T cells, under extraordinary conditions. Results indicate that shortly after adolescence, immature T cell precursors of PHA-responsive cells in the thymus, and perhaps the periphery, are the sole source of PHA-responsive T cells. T cell migration and maturation is discussed in relation to thymic hormones and the thymic-neuroendocrine regulatory axis.

Isolation and structural studies of porcine, ovine and murine thymosin beta 4 by high-performance liquid chromatography

Rapid high-performance liquid chromatographic (HPLC) procedures have been used to isolate and characterize thymosin beta 4 from different species. Crude extracts termed thymosin fraction 5A were prepared from porcine and ovine thymus glands as well as murine spleen. Each fraction 5A preparation was then fractionated by HPLC on a muBondapak C18 reversed-phase column. Porcine and ovine thymus fraction 5A, and murine spleen 5A, each yields a predominant peak at a retention time similar to that of bovine thymosin beta 4. Amino acid analysis as well as HPLC tryptic peptide mapping of these peaks indicate that they have homologous sequences to bovine thymosin beta 4. Chromatographic analysis of fresh murine thymus and spleen tissues also revealed protein peaks at the position of bovine beta 4, suggesting that thymosin beta 4 is the native protein present in the animal tissues.

Immunologically active nonapeptide fragment of a proline-rich polypeptide from ovine colostrum: amino acid sequence and immunoregulatory properties

It has been previously found that a proline-rich polypeptide (PRP) isolated from ovine colostrum has a regulatory effect on the immune response. To study the relationship between the structure of PRP and its immunomodulatory properties, the polypeptide was digested by chymotrypsin. Products of the proteolysis were separated by gel filtration and three fractions were obtained: PRP-1, PRP-2 and PRP-3. The activity of the fractions was compared with the activity of the untreated PRP. It was found that PRP-1 was inactive, whereas PRP-2 and PRP-3 showed an activity in the regulation of the immune response assayed by measurement of PFC, and by studying effects on delayed hypersensitivity, formation of autologous rosette-forming cell, and sensitivity of thymocytes to hydrocortisone. The activity of PRP-2 and PRP-3 was comparable to the activity of PRP. The PRP-3 fraction of low mol. wt was further purified and a pure nonapeptide of mol. wt 1000 (PRP-3b) was isolated. The amino acid sequence of PRP-3b was: Val--Glu--Ser--Tyr--Val--Pro--Leu--Phe--Pro. The nonapeptide showed the full spectrum of biological activities of PRP. Comparison of terminal amino acid suggested that PRP-3b was neither the NH2- nor the COOH-terminal fragment of PRP. The amino acid sequence of the nonapeptide indicated that PRP-3b is different from other known immunomodulators.

Isolation of thymosin alpha 1 from thymosin fraction 5 of different species by high-performance liquid chromatography

High-performance liquid chromatography (muBondapak C18 column with 0.05% trifluoroacetic acid in acetonitrile as solvent system) was used to isolate thymosin alpha 1 (alpha 1) from thymosin fraction 5 (f5) of various species (calf, pig, sheep and mouse). Each of the f5 preparations gave a protein peak similar in retention time to bovine thymosin alpha 1. This peak coincided with the immunoreactive peak determined by a radioimmunoassay for alpha 1. Chromatographic analysis of fresh thymus tissue extracts using a high-performance liquid chromatographic similar system did not reveal a detectable protein peak or immunoreactive peak at the alpha 1 position. Our results suggest that alpha 1 may be synthesized in a precursor form in animal tissues.

Solid-phase synthesis of thymosin beta 4: chemical and biological characterization of the synthetic peptide

The chemical synthesis of thymosin beta 4 using a solid-phase procedure has been accomplished. The synthetic product was found to be homogeneous on paper electrophoresis at pH 6.5, high-performance liquid chromatography on a reversed-phase column, and isoelectric focusing using polyacrylamide gels. The synthetic material was also shown to be identical with the natural thymosin beta 4 by tryptic peptide mapping, amino acid compositional analyses, and polyacrylamide gel isoelectric focusing. Biologically, synthetic thymosin beta 4 was found to be as active as the natural compound in a terminal deoxynucleotidyltransferase induction assay and in a macrophage migration inhibition assay. The proposed structure of the peptide hormone was thus confirmed by a chemical synthesis.