Immunoassay for bovine serum thymopoietin: discrimination from splenin by monoclonal antibodies

A polyclonal rabbit anti-bovine thymopoietin antiserum was used to develop a radioimmunoassay and sandwich enzyme-linked immunosorbent (ELISA) assay for the thymic hormone thymopoietin. Both assays showed slightly less sensitivity for the closely related splenic hormone splenin (SP) than thymopoietin (TP) and markedly less sensitivity for the human as compared with the bovine polypeptides. A number of murine monoclonal antibodies specific for bovine thymopoietin were generated; they were unreactive with bovine splenin and were also unreactive with human thymopoietin and splenin. A sandwich ELISA using these monoclonal anti-TP antibodies together with polyclonal rabbit anti-TP was specific for bovine thymopoietin and measured 300-500 ng/ml thymopoietin in bovine serum. Similar approaches are being pursued to develop an immunoassay for thymopoietin in human serum.

Circadian rhythm of thymosin-alpha 1 in normal and thymectomized mice

Studies by many investigators have demonstrated that the immune system is subject to regular circadian fluctuation. Some rhythms that have been reported include circadian changes in components of the immune system, e.g., lymphocytes, and circadian variation in primary and secondary immune responsiveness. The observation that many of these rhythms are inversely correlated to the glucocorticoid rhythm has led to the suggestion that fluctuations in the immune system may be a result of the glucocorticoid circadian rhythm. This study was designed to see if thymosin-alpha 1 (Tsn-alpha 1), a 28-amino acid polypeptide isolated from bovine thymus that has been reported to influence thymocyte differentiation, might follow a circadian rhythm, and thus play a role in the periodicity of the immune system. In these experiments, groups of 10 C57BL/6 or Swiss Webster mice were sacrificed at 4- or 6-hr intervals over a 24-hr period. Serum Tsn-alpha 1 and corticosterone levels were determined by radioimmunoassay. Results from the first experiment showed that Tsn-alpha 1 undergoes a circadian rhythm (p less than 0.001) with an acrophase (time of peak levels) 1.5 hr after the onset of light, and an amplitude (amount of maximum variation from the 24-hr mean) of 0.493 ng/ml Tsn-alpha 1-like immunoreactivity. These results were confirmed in an experiment in which the animals were placed on a reversed light cycle. In a separate experiment, the Tsn-alpha 1 circadian rhythm persisted in mice thymectomized 6 mo. earlier. In this latter experiment, a significant increase in the amplitude of the corticosterone rhythm in the thymectomized relative to sham-operated controls was also observed. Although these experiments do not imply casuality, it is interesting that the time of peak Tsn-alpha 1 levels can be correlated with the time of optimal immune function.

Decrease of thymic hormone serum level in Cockayne syndrome

Previous reports concerning children with Cockayne syndrome had described decreased T cell proliferative responses and renal anomalies which could be associated with immunologic disturbances. Herein, the thymic function was evaluated by measuring the serum level of thymic hormone. This serum level was found to be undetectable or decreased in seven cases of Cockayne syndrome. Active serum concentrations varied between 0 and 1/8, whereas normal children of the same age show activity in the range between 1/16 and 1/64. In contrast, T cell function, explored by phytohemagglutinin and Concavalin A responses, and mixed lymphocyte cultures was normal. Whether or not this premature sign of immunological aging is primary or secondary to other manifestations of the syndrome is still difficult to assess.

Induction of E-rosette-promoting factor in human plasma by levamisole: an assessment in a patient with partial DiGeorge syndrome

A male infant with partial DiGeorge syndrome responded to weekly administration of levamisole (2.5 mg/kg of body weight) with an increase of circulating E-rosette-forming T cells. Thymic hormone activity in plasma appeared to be elevated to a near-normal level of 11.6 ng thymopoietin equivalent/ml after levamisole administration. The in vitro incubation studies indicated that levamisole by itself had no E-rosette-promoting ability, but a dialysable and relatively heat-stable plasma factor induced by levamisole both in the patient and in healthy individuals had E-rosette-promoting activity for the patient's lymphocytes. Such a plasma factor, however, could not be induced in all four thymectomized myasthenic subjects examined, suggesting a thymus-dependent nature of the plasma factor. These results suggest that levamisole might mediate an increased secretion of humoral factor(s) with E-rosette-promoting activity, even from such a rudimentary thymus as in the partial DiGeorge syndrome.

Serum thymic hormone activity and cell-mediated immunity in healthy neonates, preterm infants, and small-for-gestational age infants

Groups of healthy, small-for-gestational age (SGA) and preterm appropriate-for-gestational age (AGA) infants were studied at birth, 1 month, 3 months, and 12 months of age. Serum thymic hormone (TH) activity was assayed, the number of T lymphocytes in the peripheral blood was counted, and in vitro lymphocyte stimulation responses to phytohemagglutinin (PHA) were evaluated. TH activity was decreased in 1-month-old SGA infants. T cells were reduced in all low birth weight infants; the number reverted to normal by 3 months of age in preterm AGA infants, whereas it remained low for at least 12 months in the SGA group. Lymphocyte stimulation response was decreased in low birth weight infants; the extent of depression paralleled reduction in T lymphocyte number. These observations indicate that cell-mediated immunity is impaired in low birth weight newborns and reduced TH activity may be one of the pathogenetic factors involved. Persistent depression of immunocompetence may underlie the increased susceptibility of SGA infants to infection-related morbidity and mortality.

Improved radioimmunoassay technique for measuring serum thymopoietin

An improved radioimmunoassay technique for measuring serum thymopoietin has been developed which obviates the spurious displacements previously obtained with serum samples, and increases sensitivity to 20 pg. Key improvements involved further purification of labeled thymopoietin, sequential incubations to enhance sensitivity and the use of charcoal-treated serum blanks to render controls and unknown samples comparable to the standard curve.

[The cerebral cortex regulates immune responses in the mouse]

Ablation of the left cerebral cortex abrogates the production of thymic hormone, reduces the number of spleen T cells and impairs immunization with sheep erythrocytes. In addition, partial decortication inhibits the ability of sodium diethyldithiocarbamate (DTC) to increase the level of circulating thymic hormone, as well as the number of splenic T cells. Therefore, the cerebral cortex would display an important role to maintain body integrity and relations with the external environment, through its effects on the immune system.

Serum thymic hormone activity in protein-energy malnutrition

To characterize the underlying mechanisms of impaired cell-mediated immunity in protein-energy malnutrition, thymic hormone activity was measured in the serum samples of undernourished children and was found to be reduced in the majority. This indicates that the cellular immunological deficit in nutritional deficiency may be due to reduced thymic inductive activity.

Myasthenia gravis, thymectomy and serum thymic hormone activity

Serum thymic hormone activity was measured in 36 patients with myasthenia gravis and in 10 control subjects from each age decade. In all 25 patients under 50 years of age results were within, or close to, the normal range. Activity at levels considered normal for juveniles was detected in 10 of the 11 older patients whereas levels normally decline in older subjects. One week after thymectomy, 13 of 17 patients (76 per cent) had no demonstrable serum thymic hormone activity. However, 10 months or longer after thymectomy only five patients (30 per cent) lacked thymic hormone activity in the serum. There was a significant correlation between clinial improvement and sustained lowering of serum thymic hormone activity after thymectomy.

Neonatal thymus grafts. I. Studies on the regulation of the level of circulating thymic factor (FTS)

The level of circulating thymic factor (FTS) tested by its action on spleen rosette-forming cells from adult thymectomized mice, has been shown to be stable in young animals. This stability suggests a regulatory mechanism. An approach of this regulation has been attempted by disrupting the FTS level either by neonatal thymus grafting in adult normal and thymectomized animals, or by injections of synthetic thymic factor into normal, thymectomized mice, grafted or ungrafted. In all cases, after an initial increase over the normal value, FTS levels returned close to the previous range, indicating the existence of some homeostatic mechanism of FTS secretion.

Decreased serum thymic factor activity in asthmatic children

Serum thymic factor (STF) activity was assayed in 26 young asthmatic patients and in 20 age-and sex-matched controls, in view of the increasing importance attributed to this thymic product in regulating several immune mechanisms. Determinations of total and specific IgE and of other immunoglobulins and skin tests were also performed. Decreased STF activity and high total and specific IgE concentrations were observed in the majority of asthmatic patients. In controls, STF activity was within normal limits in all cases and total and specific IgE concentrations were increased only on one case. The decreased STF activity may be responsible for a possible impairment of cell-mediated immunity and for the increased stimulation of the reaginic system observed in asthmatic patients, via its effects on some T cell subpopulation, namely, suppressor T lymphocytes, which seem particularly sensitive to STF variations. On the basis of these data and of the results of our study, a possible, although speculative, correlation between reduced STF activity and high IgE concentrations in asthmatic patients may be postulated. The reported increased occurrence of autoimmune phenomena in asthmatic patients is in agreement with the hypothesis of a STF-mediated suppressor T-lymphocyte quantitative and/or qualitative defect in this disease.

Plasma thymic hormone activity in patients with chronic mucocutaneous candidiasis

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

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