A. Astaldi

The in vitro effect of a thymic epithelial culture supernatant on mixed lymphocyte reactivity and intracellular cAMP levels of thymocytes and on antibody production to SRBC by nu/nu spleen cells

Abstract Addition of supernatants from rat thymic epithelial cultures (TES) to rat thymocytes stimulated with T-cell-mitogens or allogeneic cells leads to an increase in 14 C-TdR incorporation. Furthermore, in the presence of TES, spleen cells from athymic nu/nu mice exhibit an enhanced in vitro antibody production to SRBC, whereas TES has no such effect on spleen cells from T-cell-deprived mice. If TES is added together with thymocytes to T-cell-deprived spleen cell cultures, the number of plaque-forming cells to SRBC is enhanced, suggesting that TES induces a helper cell function in thymocytes which, if added alone, have no effect. TES also increases intracellular levels of cAMP in thymocytes in vitro and appears to act on a membrane site distinct from the β-adrenergic receptor. TES fails to affect mitogen responses, MLR and cAMP levels of lymphocytes from other lymphoid organs. The biological activity of TES as compared to that of thymic extracts is discussed.

Changes in human T lymphocytes after thymectomy and during senescence

Peripheral lymphocytes from individuals who had been thymectomized in adult life for myasthenia gravis (MG) or for other, nonimmunological reasons showed a moderate decrease in proliferative response capacity to several T-cell mitogens as compared to lymphocytes from normal individuals. The decrease of the response to mitogens and allogeneic lymphocytes was 20–30% within 5 years after thymectomy and about 50% more than 15 years after thymectomy. A comparable decrease in lymphocyte proliferative response capacity was found in healthy aged humans (68–97 years old). Analysis of T lymphocytes from both aged and thymectomized individuals with monoclonal (OKT) antibodies showed a similar pattern: the proportion of T lymphocytes binding OKT3 was reduced, and the OKT4/OKT8 ratio was increased. Hardly any T lymphocytes binding OKT6, OKT10, or OKT1 were found. A biochemical parameter for human T-cell differentiation, the lactate dehydrogenase (LDH) isoenzyme pattern, showed a significantly lower H/M ratio in the group of elderly people compared to young individuals. Furthermore, among patients thymectomized for MG, a significant correlation was observed between the LDH isoenzyme pattern of the T lymphocytes and the proliferative response to mitogens of these cells. In contrast, in healthy thymectomized individuals the LDH isoenzyme pattern appeared to be normal. These findings indicate that, after thymectomy or involution of the thymus, at least part of the peripheral blood T lymphocytes have properties different from those of the cells of young individuals. These cells might represent immature and/or not fully differentiated lymphocytes.

Characterization of physically different human T-cell subsets with monoclonal antibodies and biochemical markers

Abstract Human T cells from thymus and blood, separated into subpopulations on continuous density gradients, were investigated for binding of monoclonal antibodies and activity of several enzymes. According to those parameters, several differences related to the specific gravity of the cells were found. Virtually all heavy thymocytes were positive for the monoclonal antibodies OKT10, 8, 6, and 4, but did not bind to OKT3. In contrast, a substantial part of the light thymocytes bound OKT3 and OKT4, but did not bind OKT6 and OKT8. In blood, heavy T lymphocytes were enriched in cells positive for OKT8, whereas light lymphocytes contained more OKT4-positive cells. Heavy peripheral T cells and thymocytes, which had an immature isoenzyme pattern of lactate dehydrogenase (LDH), and a poor proliferative response in vitro, had low activities of 5′-nucleotidase (5′NT) and of purine nucleoside phosphorylase (PNP) and a high activity of adenosine deaminase. Light peripheral T cells had a more mature LDH isoenzyme pattern and higher activities of 5′NT and PNP. We conclude that the poor proliferative response in vitro of heavy peripheral T cells must be due to multiple intrinsic properties, including a low stage of maturation and the occurrence of (precursors for) suppressor cells.

Thymus-dependent serum factor in nonthymectomized and thymectomized patients with myasthenia gravis

Abstract The activity of a thymus-dependent factor (SF) was determined in the sera of 145 healthy controls and 111 patients with myasthenia gravis. Evidence for an age-related decline in the activity was obtained, both in normal donors and in the patients. SF activity appeared to be absent from most of the thymectomized patients: after thymectomy the SF activity decreased rapidly, reaching very low levels within a few days. No clear correlation was found between the activity of SF in the sera of the patients and their clinical stage of disease.

A thymus-dependent serum factor induces maturation of thymocytes as evaluated by graft-versus-host reaction

Abstract Mouse thymocytes were incubated in vitro in the presence of a thymus-dependent serum factor. This factor increases the level of cellular cyclic AMP but does not affect the number of proliferating cells. After incubation with the factor, C57BL/6J thymocytes were injected into new born (C57BL/6J × C3H)F 1 hybrids. The capability of thymocytes to elicit a graft-versus-host reaction in vivo was evaluated by the spleen weight assay. Thymocytes treated with the thymic factor were found to induce a more effective graft-versus-host reaction as compared with untreated thymocytes and with thymocytes treated with inactivated thymic factor. These results are consistent with the existence of a thymocyte maturation pathway which does not involve cell proliferation and is under the influence of thymic factors.

Early events in thymocyte activation. I. Stimulation of protein synthesis by a thymus-dependent human serum factor

Abstract Human serum contains a thymus-dependent factor that raises cyclic AMP levels in thymocytes. We found that this factor stimulates protein synthesis in thymocytes cultured in vitro. This activity of serum factor is thymus-dependent, because it is absent in sera from thymectomized donors; furthermore, this effect is predominantly found on precursors of mature T cells. Incubation of thymocytes with other agents that increase cyclic AMP, induces an increase in protein synthesis similar to that observed with serum factor. Most likely, the increase in protein synthesis is one of the events following stimulation of adenylate cyclase in thymocytes that leads to cell differentiation.

Serum thymic factor in subacute sclerosing panencephalitis patients.

Abstract The activity of thymus-dependent serum factor (SF) was measured in 11 patients with subacute sclerosing panencephalitis (SSPE). A significantly decreased activity was found in 6 out of 11 patients, whereas the level of cyclic AMP in lymphocytes of the patients, a parameter for the maturation of peripheral blood lymphocytes, showed low values in 9 out of 11 patients. These findings were compared with the clinical stage of the disease and with some lymphocyte functions in vitro . No correlation was found between the SF levels and the amount of cyclic AMP in the lymphocytes or between these two parameters and the lymphocyte functions in vitro . It is concluded that a thymic humoral dysfunction is unlikely to play a role in the pathogenesis of SSPE; it appears that such a dysfunction is rather a secondary event in this disease.

THYMUS-DEPENDENT HUMAN SERUM FACTOR ACTIVE ON PRECURSORS OF MATURE T CELLS

Publisher Summary This chapter discusses the thymus-dependent human serum factor (SF) that is active on precursors of mature T cells. The chapter describes the effect of SF on cAMP level in different target cells as compared to prostaglandin (PGE1), a substance known to increase cAMP in lymphoid and nonlymphoid cells. In a study described in the chapter, SF markedly increased the level of cAMP in thymocytes, moderately in lymph node cells, and only marginally in spleen cells. Because SF does not induce any increase in the level of cAMP in mature T cells such as hydrocortisone (HC)-resistant mouse thymocytes and human peripheral blood T cells, it may be concluded that SF selectively stimulates cAMP synthesis in precursors of mature T cells. Such precursors are known to be present in small numbers among spleen cells and lymph node cells and to represent a substantial portion of HC-sensitive thymocytes.

A thymus-dependent human serum factor induces a decrease of terminal deoxynucleotidyl transferase in thymocytes

Abstract Previously, we have shown that a thymus-dependent human serum factor (SF) selectively acts on hydrocortisone-sensitive, immunologically immature thymocytes, inducing hydrocortisone resistance and immunological maturation as evaluated by graft-vs-host reaction. Human and mouse thymocytes were incubated with SF for different times and the activity of terminal deoxynucleotidyl transferase (TdT) was measured hereafter. A marked decrease of TdT activity was found in thymocytes exposed to SF for 240 min. These data indicate that the maturation of thymocytes induced by SF is accompanied by a decrease of TdT activity.

T-Cell Profile and Reactivity in vitro During Immune Reconstitution Following Bone Marrow Transplantation

Abstract Shortly after bone marrow transplantation for aplastic anemia the T-cell profile in peripheral blood, identified by monoclonal antibodies 0KT, is compatible with the presence of immature T cells, i.e. increased binding of 0KT 10 (thymocytes) and reversed 0KT 4 (helper/inducer T) to 0KT8 (cytotoxic/suppressor T) ratio; the lymphocyte responses in vitro are decreased. On recovery of reactivity in vitro, no correlation with the profile of 0KT binding of PBL is seen, except for a crossing of a threshold of 20% 0KT4+cells before responsiveness to mitogens increases.