Receptors for thymosin alpha 1 on mouse thymocytes

Thymosin alpha 1 is able to act in vitro to stimulate T-cell precursors and to induce surface markers. The initial mechanism by which alpha 1 activates T cells could be the binding of alpha 1 to cell membranes. Using a specific anti-alpha 1 antibody and an indirect immunofluorescence procedure it was found that thymosin alpha 1 binds to the surface of a large portion of murine lymphocytes. Furthermore, thymocytes have been fractionated into immature and mature subpopulations by using the peanut agglutinin (PNA) technique. It was found that PNA+, immature cells showed specific receptors for alpha 1 on the cell membrane.

T-cell abnormalities after mediastinal irradiation for lung cancer. The in vitro influence of synthetic thymosin alpha-1

The effects of mediastinal irradiation (RT) on the numbers and functions of purified peripheral blood T-lymphocytes from patients with locally advanced non-small cell lung cancer were evaluated. The patients were candidates for a randomized trial to evaluate the immunorestorative properties of synthetic thymosin alpha-1. Twenty-one patients studied before RT did not exhibit any significant difference in T-cell numbers or function compared to age-matched healthy subjects. However, 41 patients studied within 1 week after completing RT exhibited significant depressions of E-rosette-forming cells at 4 degrees C (E4 degrees-RFC)/mm3, E-rosette-forming cells at 29 degrees C (E29 degrees-RFC)/mm3, OKT3/mm3, OKT4/mm3, and OKT8/mm3 (P = 0.0001); total T-cell percentages (%OKT3, P = 0.01); and T-cell proliferative responses in mixed lymphocyte cultures (MLR) (P = 0.01) and to the mitogen phytohemagglutinin under suboptimal conditions (P less than or equal to 0.03). Nine patients studied before and after RT showed a significant increase in OKT4/OKT8 (P = 0.01) following RT. A short-term in vitro incubation with thymosin alpha-1 could enhance MLR of T-cells in 12 of 27 patients with post-RT abnormalities. In 13 patients who were treated with placebo, the RT-induced depression of T-cell numbers and function persisted for at least 3 to 4 months. In addition, in 12 patients progressive decreases developed in %E4 degrees-RFC, %OKT3, %OKT4, and OKT4/OKT8, which always preceded clinical relapse. This study indicates that mediastinal RT results in prolonged depletion of circulating T-cells, alterations of T-cell subset proportions, and intrinsic T-cell functional deficiencies. This patient population provides a uniformly immunosuppressed group of subjects with which to evaluate the immunorestorative effects of thymosin alpha-1 or other biologic response modifiers.

Mechanism of action of thymosin. I. Thymosin fraction 5 increases lymphokine production by mature murine T cells responding in a mixed lymphocyte reaction

The effect of thymosin on the murine thymocyte mixed lymphocyte response was studied. Thymosin fraction 5 (TF5) caused a two- to threefold enhancement of the proliferative response and production of IL 2 when murine thymocytes were cultured with alloantigenic stimulator cells. Production of a second lymphokine, CSF, was increased up to sevenfold. The target cell for thymosin was a mature T cell, because the PNA- subpopulation of thymocytes, as well as peripheral lymph node lymphocytes, responded to culture with TF5 and alloantigen by enhanced proliferation and lymphokine production. The active component of TF5 appears to be one or more as yet unidentified peptides, because neither of the well-characterized TF5 component peptides, alpha 1 or beta 4, were active. After incubation with TF5 in primary culture, cells remaining after 10 to 14 days were increased both in number and in secondary response to alloantigen, as measured by lymphokine production. These results suggest that TF5 contains one or more biologically active components which can modulate mature T cell activity and lymphokine production, and which provide the basis for understanding some of the previously reported diverse effects of thymosin.

Mechanism of action of thymosin. I. Thymosin fraction 5 increases lymphokine production by mature murine T cells responding in a mixed lymphocyte reaction

The effect of thymosin on the murine thymocyte mixed lymphocyte response was studied. Thymosin fraction 5 (TF5) caused a two- to threefold enhancement of the proliferative response and production of IL 2 when murine thymocytes were cultured with alloantigenic stimulator cells. Production of a second lymphokine, CSF, was increased up to sevenfold. The target cell for thymosin was a mature T cell, because the PNA- subpopulation of thymocytes, as well as peripheral lymph node lymphocytes, responded to culture with TF5 and alloantigen by enhanced proliferation and lymphokine production. The active component of TF5 appears to be one or more as yet unidentified peptides, because neither of the well-characterized TF5 component peptides, alpha 1 or beta 4, were active. After incubation with TF5 in primary culture, cells remaining after 10 to 14 days were increased both in number and in secondary response to alloantigen, as measured by lymphokine production. These results suggest that TF5 contains one or more biologically active components which can modulate mature T cell activity and lymphokine production, and which provide the basis for understanding some of the previously reported diverse effects of thymosin.

Experimental allergic encephalomyelitis in guinea pigs. Influence of thymosin fraction V on the disease

Experimental allergic encephalomyelitis (EAE) was induced in strain 13 guinea pigs by sensitization with 10 micrograms of myelin basic protein (BP) in complete Freund's adjuvant (CFA). These animals were treated with saline or with thymosin factor V in 3 different doses in 3 separate experiments. Thymosin had no suppressive effect on the incidence and severity of EAE.

Adipoblasts from the Zucker fafa rat

In vitro experiments using both primary fetal hepatocyle cultures and adipoblast cultures have demonstrated that the presence of the fa gene is associated with decreased synthetic capacity, when compared to wild-type cultures. These results are in contrast to the elevated lipogensis and lipoprotein-lipase activities found in vivo in young adult obses (fafa) Zucker rats compared to their lean littermates. These studies used adipoblast cultures to address three possible explanations for these in vitro-in vivo differences: 1) FaFa and fafa adipoblast cultures represent different cell populations with intrinsically different abilities to differentiate, ie, to lipid-fill. 2) The decreased synthetic capacities in fafa vs FaFa adipoblast cultures are specific to cultures derived from the epididymal pad. 3) Cultured adipoblasts produce factor(s) that affect adipoblast differentiation in vitro. Results indicate that 1) the rate of differentiation is slower in fafa than in FaFa adipoblasts 2) there are depot-related differences in lipid metabolism, but these differences do not negate the in vitro association between the fa gene and decreased synthetic capacity and 3) FaFa epididymal-derived adipoblasts produce a factor(s) that affects inguinal-derived adipoblast differentiation and/or growth in vitro. Thus it is important to take both the site of cell origin and culture conditions into consideration when using in vitro systems as an approach to understanding complex in vivo disorders, such as obesity in the Zucker fafa rat.

Thymosins, lymphokines, and the immunology of aging

Recent data point to a significant role for thymosins, lymphokines, and other soluble mediators in the senescence of the immune response that occurs with aging. In recent years, considerable progress has been made in the isolation and physiochemical characterization of several of these soluble mediators. We are now beginning to define the mechanisms by which these molecules regulate and mediate immune responses. In this paper we review the properties of the best characterized thymic hormones and lymphokines and focus on the role of the endocrine thymus in modulating immune responses. Of particular interest is the recent observation that thymosin fraction 5 can enhance production of interleukin-2 (IL-2) and colony-stimulating factor (CSF), and that IL-2 production, but not CSF production, is selectively diminished in aging mice. Several of the products of the immune system also can act as neuroactive immunotransmitters and modulate a number of neuroendocrine responses. Current studies point to an important role for these molecules in modulating neuroendocrine function, suggesting a broader role for the endocrine thymus in the aging process.

Immunologic studies of the acquired immune deficiency syndrome: relationship of immunodeficiency to extent of disease

Immunologic and conventional laboratory studies were done in 135 previously untreated subjects including 28 (20.7%) symptom-free homosexuals and 74 (54.8%) with ARC and 33 (24.5%) with AIDS. More than half of all patients had abnormal percentages of lymphocytes, percentages of T3+ cells, percentage and absolute number of T4+ cells, percentage of T8+ cells, T4/T8 ratio, monocyte adherence, and serum thymosin alpha 1. Most immune variables worsened with progressive disease. Low lymphocyte 5'nucleotidase increased suppressor cell activity, and impaired IL-2 and alpha interferon production and response suggest diminished mature and increased immature peripheral blood and tissue T cells. These findings suggest approaches to staging, prognostication, and treatment for AIDS.

Specific antibody synthesis in vitro. II. Age-associated thymosin enhancement of antitetanus antibody synthesis

A decline in T cell function accounts for many of the observed age-related deficient immune responses. Specific antibody response to many antigens requires T cell cooperation, and deficient antibody response to such antigens has been demonstrated with aging. In an effort to assess the potential reconstitutive capacity of Thymosin Fraction 5, in vitro antitetanus antibody production was measured in tetanus toxoid booster-immunized young and old volunteers. 22 young and 12 old volunteers were immunized with tetanus toxoid and plasma antitetanus antibody and in vitro lymphocyte production of antitetanus antibody was measured. Plasma antitetanus antibody response was significantly greater in the young. In vitro antitetanus antibody synthesis was negligible prior to immunization and peaked in cultures established 1 week after immunization from both young and old. When Thymosin Fraction 5 was added to the cultures, however, there was a dose-related enhancement of antibody synthesis in 7 of 10 from the group of elderly volunteers, but only 3 of 12 from the younger group. Our data indicate that specific antibody response is deficient in the elderly, but can be enhanced in vitro by thymosin. A future clinical trial of thymosin as an adjuvant to active immunization for the elderly is warranted.

Inverse correlation between age related abnormalities of T-cell immunity and circulating thymosin alpha 1 levels in haemophilia A

T-cell immunity and serum levels of thymosin alpha 1, beta 2-microglobulin, circulating immune complexes, serum immunoglobulin levels, antibodies to hepatitis surface or core antigen, and to cytomegalovirus, and Epstein-Barr virus were investigated in 51 patients with haemophilia A ranging in age from 2 to 52 years. All patients had received commercial U.S. lyophilized concentrates of antihaemophilic factor (AHF). The mean helper/cytotoxic-suppressor (OKT4/OKT8) ratio of 11 pre-adolescents (1.6 +/- 0.4 SE) was not significantly different from that of age matched normal controls. In contrast, the mean OKT4/OKT8 ratios of 13 adolescent (1.2 +/- 0.2 SE) and 23 adult (0.8 +/- 0.1 SE) haemophiliacs were significantly reduced. Abnormalities of lymphocyte mitogenic responses were found only in adult haemophiliacs. Nine individuals treated with commercial U.S. prothrombin complex concentrates for antibodies directed against AHF or for haemophilia B had normal mean OKT4/OKT8 values. The mean serum thymosin alpha 1 levels for each age category was similar to that of age matched controls; however, regression analysis revealed a significant relationship between elevated thymosin alpha 1 levels and decreased OKT4/OKT8 ratios in adult haemophiliacs (P = 0.012). Although the mean serum level of beta 2-microglobulin was significantly increased in the adult haemophiliac group, there was no correlation between OKT4/OKT8 ratios and any of the other serologic parameters studied.

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.

Antibody to human T-cell leukemia virus membrane antigens, beta 2-microglobulin levels, and thymosin alpha 1 levels in hemophiliacs and their spouses

Recently, antibodies to human T-cell leukemia virus membrane antigens (HTLV-MA) and elevated levels of beta 2-microglobulin and thymosin alpha 1 have been found with high frequency in patients with the acquired immunodeficiency syndrome. Prospective studies of asymptomatic persons at high risk for this syndrome will ascertain whether any of these findings is a predictive marker for the disease. In this study, antibodies to HTLV-MA, beta 2-microglobulin levels, and thymosin alpha 1 levels were determined for a group of asymptomatic adult hemophiliacs and their wives. Five of thirty-nine hemophiliacs had HTLV-MA antibody, compared with none of 21 wives tested. The mean beta 2-microglobulin level for hemophiliacs was significantly higher than the control value (p less than 0.001), whereas the wives had a normal mean value. The mean thymosin alpha 1 values were normal for hemophiliacs and their wives; however, 3 of 22 hemophiliacs and 1 of 16 wives had abnormally high levels. Whether any of these abnormalities correlate with subsequent development of the acquired immunodeficiency syndrome will be ascertained by longitudinal follow-up of this population.

Immunochemical studies on thymosin: radioimmunoassay of thymosin beta 4

Thymosin beta 4, a peptide with hormonal-like properties first isolated from the thymus gland, can be measured in serum using a newly described radioimmunoassay. The radioimmunoassay utilizes an antibody raised in rabbits against synthetic thymosin beta 4 conjugated by glutaraldehyde to keyhole limpet hemocyanin. A 125I-tyrosine-C13 analogue of the biologically active C-terminal fragment is used as the radioactive tracer. The radioimmunoassay is sensitive in the nanogram range and no cross-reactivity with common serum proteins is demonstrable. High performance liquid chromatography of serum samples indicates that two thymosin beta 4 cross-reactive species are present in human serum. Levels in serum range from 450 to 1100 ng/ml and decline with age.

Immunoreactive thymosin alpha 1 is associated with murine T-cell lymphomas

Growth of murine spontaneous and transplanted AKR T-cell lymphomas results in marked elevations of serum immunoreactive thymosin alpha 1. Thymosin alpha 1 is one of the peptide hormones believed to be secreted primarily by the thymic epithelium. This elevation, however, is not mediated by the thymus but rather, seems to be directly associated with the tumor cells. Growth of a B-cell lymphoma does not generate elevated immunoreactive thymosin alpha 1 in the serum, thus, a thymosin alpha 1-like peptide is selectively associated with these T-cell lymphomas. The possible relationship between expression of T-leukemia viruses and alpha 1 expression is discussed.

Estrogen and thymic hormone interactions in the female mouse

This study showed that there are relationships between thymic and adrenal/ovarian endocrine actions. A 4 mg/kg dose of thymosin fraction 5 (TSN5) advanced vaginal opening and elevated estrogen levels. Single estradiol benzoate (EB) injections decreased thymus weight and caused a transient reduction in circulating plasma levels of thymosine alpha 1 (TSN alpha 1), a peptide component of TSN5. Circulating estrogen levels were elevated when TSN alpha 1 levels were undetectable. Also, TSN alpha 1 levels decreased with age and after a prolonged athymic state. The thymus was shown to involute after a single TSN5 injection, suggesting the existence of a negative hormonal feedback on the thymus. Additionally thymectomy at 3 days of age was shown to delay vaginal opening while thymectomy at 30 days of age failed to produce any significant effect on reproductive maturation. Although much research is still needed, our results provide additional evidence of a relationship between the endocrine thymus and ovary.

The thymus-adrenal connection: thymosin has corticotropin-releasing activity in primates

Endotoxin-free thymosin fraction 5 elevated corticotropin, beta-endorphin, and cortisol in a dose- and time-dependent fashion when administered intravenously to prepubertal cynomolgus monkeys. Two synthetic component peptides of thymosin fraction 5 had no acute effects on pituitary function, suggesting that some other peptides in thymosin fraction 5 were responsible for its corticotropin-releasing activity. In agreement with these observations, total thymectomy of juvenile macaques was associated with decreases in plasma cortisol, corticotropin, and beta-endorphin. These findings indicate that the prepubertal primate thymus contains corticotropin-releasing activity that may contribute to a physiological immunoregulatory circuit between the developing immunological and pituitary-adrenal systems.

Thymosin fraction 5 does not accelerate reconstitution of immunologic reactivity after human marrow grafting

More than 1 year is required for immunologic function to recover following human marrow grafting. In an attempt to shorten the time required for immunologic reconstitution, 14 patients were treated with thymosin fraction 5 after transplantation. Two died before administration of thymosin could be completed. In the remaining 12 patients, immunologic studies were compared to those of patients who were transplanted but did not receive thymosin. While five patients had transient elevation of in vitro lymphocyte blastogenesis during thymosin treatment, results of other immunologic studies from patients treated with thymosin were similar to those from patients not treated. The subsequent development of graft-versus-host disease, major or minor infection, and leukaemic relapse was not different between the groups. Six patients are alive and five are well without problems; one has chronic graft-versus-host disease. We conclude that thymosin fraction 5 administered as described was not toxic. Although modifying some immunological parameters, thymosin did not appear to alter the incidence of graft-versus-host disease, infection or leukaemic relapse or to accelerate immunologic reconstitution.

Immunomodulation of murine B16 melanoma metastasis: thymosin, thymectomy and irradiation

Thymosin, a product of the endocrine system, was used to further define the effects of immunomodulation of metastasis. Adult thymectomized C57BL/6 mice, 4 wk post-irradiation (400 R) had a decrease in the number of pulmonary metastasis (compared to controls) following tail vein injection of 5 X 10(4) B16 melanoma cells. Thymosin fraction 5 (fr. 5) administration (200 micrograms/mouse, 3 times weekly beginning 2 days post-thymectomy) returned the number of metastasis to the nonthymectomized values. Thymosin treatment of sham-operated, sham-operated irradiated, or thymectomized nonirradiated mice did not significantly elevate the number of metastases compared to the respective controls. Variant tumors which have an increase in metastasis following thymectomy and irradiation were also used. Thymosin administration reversed the effects of thymectomy in such variants, resulting in a decrease in metastasis. Metastases in thymosin-treated control mice were not significantly altered. A role for the thymus in metastasis via an endocrine product (thymosin) is suggested by these studies. Since thymosin did not increase metastasis in intact mice with tumors, further clinical trials with thymosin in cancer patients are not counterindicated by our results. These experiments confirm that thymosin fr. 5 is an important probe of the immunoendocrine events involved in tumor growth and metastasis.