In spite of considerable evidence on the regulation of immunity by thyroid hormones, the impact of the thyroid status in tumor immunity is poorly understood. Here, we evaluated the antitumor immune ...responses evoked in mice with different thyroid status (euthyroid, hyperthyroid, and hypothyroid) that developed solid tumors or metastases after inoculation of syngeneic T lymphoma cells. Hyperthyroid mice showed increased tumor growth along with increased expression of cell cycle regulators compared to hypothyroid and control tumor-bearing mice. However, hypothyroid mice showed a higher frequency of metastases than the other groups. Hyperthyroid mice bearing tumors displayed a lower number of tumor-infiltrating T lymphocytes, lower percentage of functional IFN-γ-producing CD8
+
T cells, and higher percentage of CD19
+
B cells than euthyroid tumor-bearing mice. However, no differences were found in the distribution of lymphocyte subpopulations in tumor-draining lymph nodes (TDLNs) or spleens among different experimental groups. Interestingly, hypothyroid TDLN showed an increased percentage of regulatory T (Treg) cells, while hyperthyroid mice displayed increased number and activity of splenic NK cells, which frequency declined in spleens from hypothyroid mice. Moreover, a decreased number of splenic myeloid-derived suppressor cells (MDSCs) were found in tumor-bearing hyperthyroid mice as compared to hypothyroid or euthyroid mice. Additionally, hyperthyroid mice showed increased cytotoxic activity, which declined in hypothyroid mice. Thus, low levels of intratumoral cytotoxic activity would favor tumor local growth in hyperthyroid mice, while regional and systemic antitumor response may contribute to tumor dissemination in hypothyroid animals. Our results highlight the importance of monitoring the thyroid status in patients with T cell lymphomas.
Key messages
T cell lymphoma phenotype is paradoxically influenced by thyroid status.
Hyperthyroidism favors tumor growth and hypothyroidism rises tumor dissemination.
Thyroid status affects the distribution of immune cell types in the tumor milieu.
Thyroid status also modifies the nature of local and systemic immune responses.
Thyroid hormones play critical roles in differentiation, growth and metabolism, but their participation in immune system regulation has not been completely elucidated. Modulation of in vivo thyroid ...status was used to carry out an integrative analysis of the role of the hypothalamus-pituitary-thyroid (HPT) axis in T and B lymphocyte activity. The participation of the protein kinase C (PKC) signaling pathway and the release of some cytokines upon antigenic stimulation were analyzed. Lymphocytes from hyperthyroid mice displayed higher T-and B-cell mitogen-induced proliferation, and those from hypothyroid mice displayed lower T- and B-cell mitogen-induced proliferation, compared with euthyroid animals. Reversion of hypothyroid state by triiodothyronine (T3) administration recovered the proliferative responses. No differences were found in lymphoid subset balance. Both total PKC content and mitogen-induced PKC translocation were higher in T and B cells from hyperthyroid mice, and lower in cells from hypothyroid mice, compared with controls. Levels of thyroid-stimulating (TSH) and TSH-releasing (TRH) hormones were not directly related to lymphocyte proliferative responses. After immunization with sheep red blood cells (SRBCs) and re-stimulation, in vitro spleen cells from hyper- or hypothyroid mice showed, respectively, increased or decreased production of interleukin (IL)-2 and interferon (IFN)-gamma cytokines. Additionally, an increase in IL-6 and IFN-gamma levels was found in hyperthyroid cells after in vivo injection and in vitro re-stimulation with lipopolysaccharide (LPS). Our results show for the first time a thyroid hormone-mediated regulation of PKC content and of cytokine production in lymphocytes; this regulation could be involved in the altered responsiveness to mitogen-induced proliferation of T and B cells. The results also confirm the important role that these hormones play in regulating lymphocyte reactivity.
We have shown in vitro that thyroid hormones (THs) regulate the balance between proliferation and apoptosis of T lymphoma cells. The effects of THs on tumor development have been studied, but the ...results are still controversial. Herein, we show the modulatory action of thyroid status on the in vivo growth of T lymphoma cells. For this purpose, euthyroid, hypothyroid, and hyperthyroid mice received inoculations of EL4 cells to allow the development of solid tumors. Tumors in the hyperthyroid animals exhibited a higher growth rate, as evidenced by the early appearance of palpable solid tumors and the increased tumor volume. These results are consistent with the rate of cell division determined by staining tumor cells with carboxyfluorescein succinimidyl ester. Additionally, hyperthyroid mice exhibited reduced survival. Hypothyroid mice did not differ significantly from the euthyroid controls with respect to these parameters. Additionally, only tumors from hyperthyroid animals had increased expression levels of proliferating cell nuclear antigen and active caspase 3. Differential expression of cell cycle regulatory proteins was also observed. The levels of cyclins D1 and D3 were augmented in the tumors of the hyperthyroid animals, whereas the cell cycle inhibitors p16/INK4A (CDKN2A) and p27/Kip1 (CDKN1B) and the tumor suppressor p53 (TRP53) were increased in hypothyroid mice. Intratumoral and peritumoral vasculogenesis was increased only in hyperthyroid mice. Therefore, we propose that the thyroid status modulates the in vivo growth of EL4 T lymphoma through the regulation of cyclin, cyclin-dependent kinase inhibitor, and tumor suppressor gene expression, as well as the stimulation of angiogenesis.
Thyroid hormones are important regulators of cell physiology, inducing cell proliferation, differentiation or apoptosis, depending on the cell type. Thyroid hormones induce proliferation in ...short-term T lymphocyte cultures. In this study, we assessed the effect of long-term thyroxine (T4) treatment on the balance of proliferation and apoptosis and the intermediate participants in T lymphoma cells. Treatment with T4 affected this balance from the fifth day of culture, inhibiting proliferation in a time-dependent manner. This effect was associated with apoptosis induction, as characterized through nuclear morphological changes, DNA fragmentation, and Annexin V-FITC/Propidium Iodide co-staining. In addition, increased iNOS gene and protein levels, and enzyme activity were observed. The generation of reactive oxygen species, depolarization of the mitochondrial membrane, and a reduction in glutathione levels were also observed. The imbalance between oxidants and antioxidants species is typically associated with the nitration of proteins, including PKCζ, an isoenzyme essential for lymphoma cell division and survival. Consistently, evidence of PKCζ nitration via proteasome degradation was also observed in this study. Taken together, these results suggest that the long-term culture of T lymphoma cells with T4 induces apoptosis through the increased production of oxidative species resulting from both augmented iNOS activity and the loss of mitochondrial function. These species induce the nitration of proteins involved in cell viability, promoting proteasome degradation. Furthermore, we discuss the impact of these results on the modulation of T lymphoma growth and the thyroid status in vivo.
Hypothyroidism exerts deleterious effects on immunity, but the precise role of the hypothalamic–pituitary–thyroid (HPT) axis in immunoregulatory and tolerogenic programs is barely understood. Here, ...we investigated the mechanisms underlying hypothyroid‐related immunosuppression by examining the regulatory role of components of the HPT axis. We first analyzed lymphocyte activity in mice overexpressing the TRH gene (Tg‐Trh). T cells from Tg‐Trh showed increased proliferation than wild‐type (WT) euthyroid mice in response to polyclonal activation. The release of Th1 pro‐inflammatory cytokines was also increased in Tg‐Trh and TSH levels correlated with T‐cell proliferation. To gain further mechanistic insights into hypothyroidism‐related immunosuppression, we evaluated T‐cell subpopulations in lymphoid tissues of hypothyroid and control mice. No differences were observed in CD3/CD19 or CD4/CD8 ratios between these strains. However, the frequency of regulatory T cells (Tregs) was significantly increased in hypothyroid mice, and not in Tg‐Trh mice. Accordingly, in vitro Tregs differentiation was more pronounced in naïve T cells isolated from hypothyroid mice. Since Tregs overexpress galectin‐1 (Gal‐1) and mice lacking this lectin (Lgals1−/−) show reduced Treg function, we investigated the involvement of this immunoregulatory lectin in the control of Tregs in settings of hypothyroidism. Increased T lymphocyte reactivity and reduced frequency of Tregs were found in hypothyroid Lgals1−/− mice when compared to hypothyroid WT animals. This effect was rescued by the addition of recombinant Gal‐1. Finally, increased expression of Gal‐1 was found in Tregs purified from hypothyroid WT mice compared with their euthyroid counterpart. Thus, a substantial increase in the frequency and activity of Gal‐1‐expressing Tregs underlies immunosuppression associated with hypothyroid conditions, with critical implications in immunopathology, metabolic disorders, and cancer.
The induction of galectin‐1 (Gal‐1)‐producing regulatory T cells (Tregs) contributes to hypothyroidism‐related immunosuppression. Hypothyroid wild‐type (WT) mice display increased frequency and activity of Tregs expressing high levels of Gal‐1, which contributed to lower T‐cell proliferation and immunosuppression compared with euthyroid mice. These effects were abrogated in hypothyroid mice lacking Gal‐1 (Lgals1−/−).
The aim of the present work was to analyze the effect of chronic stress on thyroid axis and its influence on the immune response. For this purpose a murine model of chronic stress was developed to ...evaluate and to correlate thyroid hormone levels with humoral alloimmune response. Results show a reduction in serum levels of thyroid hormones, specially a significant decrease in serum levels of triiodotyronine (T
3) in stressed animals. On the other hand, alloimmunization was not able to induce an early increment in T
3 and thyroxine (T
4) levels as it was previously reported in normal animals. In addition, lower titers of alloantibodies were obtained in animals under stress conditions as compared to normal mice. The sustitutive T
4 treatment in stressed animals increased significantly alloantibody production as well as the early increment in thyroid hormones after antigenic challenge. These findings suggest that chronic stress induces an alteration of the function of thyroid axis that alters the immune response.
Zinc and iron are crucial mineral components of human diet, because their deficiency leads to several disorders, including alterations of the immune function. It has been demonstrated, in both humans ...and rodents, that a diminished number of lymphoid cells and a loss of lymphocyte activity accompany deprivation of these essential minerals. The aim of this work was to analyze if iron and/or zinc imbalances regulate lymphocyte activity and the intracellular signals involved in the effect. Mice from the BALB/c strain were fed with iron- and/or zinc-deficient or mineral-supplemented diets, according to the American Institute of Nutrition Rodent Diets. Levels of iron and zinc were assessed in blood, liver, or bone samples. Selective mitogen stimulation of T- and B-lymphocytes were performed. We found a diminished proliferative response in T- and B-lymphocytes from zinc- and/or iron-deficient animals with respect to controls. These effects were related to decreased mitogen-induced translocation of protein kinase C (PKC) activity to cell membranes on both cell types from all animals fed with deficient diets. Our results demonstrate that iron and zinc deficiencies affect both T- and B-lymphocyte function by PKC-dependent mechanisms.
Among the many examples of neuroendocrine–immune system interactions the relationship between the thyroid axis and the immune function has yet to be clearly established. Here we studied the influence ...of thyroid hormones on the course of an alloimmune response. Murine T
3 and T
4 levels were found to be increased a few days after the immunization of mice with allogeneic lymphoid cells. Besides in vivo treatment with T
4 was shown to increase alloantibody titers during the early stages of alloimmunization and to enforce lymphoid proliferation in vitro in a mixed lymphocyte reaction. Conversely, lowering thyroid hormone seric levels by propylthiouracil treatment, negatively modulates the humoral and cellular alloimmune responses. The evidence here points to the existence of a bidirectional communication between both systems. The possibility that the antigenic challenge would increase the thyroid gland activity thus leading to a positive modulatory action upon the immune response is also discussed.
Thyroid hormones are important regulators of cell physiology, inducing cell proliferation, differentiation or apoptosis, depending on the cell type. Thyroid hormones induce proliferation in ...short-term T lymphocyte cultures. In this study, we assessed the effect of long-term thyroxine (T4) treatment on the balance of proliferation and apoptosis and the intermediate participants in T lymphoma cells. Treatment with T4 affected this balance from the fifth day of culture, inhibiting proliferation in a time-dependent manner. This effect was associated with apoptosis induction, as characterized through nuclear morphological changes, DNA fragmentation, and Annexin V-FITC/Propidium Iodide co-staining. In addition, increased iNOS gene and protein levels, and enzyme activity were observed. The generation of reactive oxygen species, depolarization of the mitochondrial membrane, and a reduction in glutathione levels were also observed. The imbalance between oxidants and antioxidants species is typically associated with the nitration of proteins, including PKCzeta, an isoenzyme essential for lymphoma cell division and survival. Consistently, evidence of PKCzeta nitration via proteasome degradation was also observed in this study. Taken together, these results suggest that the long-term culture of T lymphoma cells with T4 induces apoptosis through the increased production of oxidative species resulting from both augmented iNOS activity and the loss of mitochondrial function. These species induce the nitration of proteins involved in cell viability, promoting proteasome degradation. Furthermore, we discuss the impact of these results on the modulation of T lymphoma growth and the thyroid status in vivo.PUBLICATION ABSTRACT
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