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Radiation Hormesis in Cancer
Published in T. D. Luckey, Radiation Hormesis, 2020
Radiation hormesis in immune competence is most important. It provides a reduction in mortality rates from infection, cancer, respiratory, and cardiovascular diseases; this results in increased average lifespans. Longer average lifespans in lightly irradiated populations provide increased opportunity for cancer in older individuals. Thymic involution and decreased immune competence allow more infection and cancer mortality in aging populations. In spite of this, the data consistently show decreased cancer incidence and mortality in lightly irradiated populations. When lifetime data are considered, radiation hormesis counteracts the proclivity for increased cancer in animals and humans. This is attributed to increased immune competence in previously irradiated populations. If those exposures were therapy for a specific disease, such as cancer, this would be evidence for special consideration.718
Summary and Development of a New Approach to Senescence
Published in Nate F. Cardarelli, The Thymus in Health and Senescence, 2019
The decline in immune capability with age is a well-known phenomenon. The decrease roughly correlates with thymic involution and the incidence of specific disease. As immune surveillance falls, malignancy increases. Lymphoid tissue in general involutes. Thymic hormone secretion likewise decreases with age. Adult thymectomy, while it has no dramatic results, such as seen with athymic infants, does lead to a gradual, though nevertheless greater than normal, drop in immune response. There is no question but that the thymus is involved in the age-dependent fall in various immune parameters. Involution accelerates with a number of disease states, such as diabetes.
The Thymus and Immunotherapy, Reconstructive Vs. Stimulatory or Suppressive Conceptions
Published in Marek P. Dabrowski, Barbara K. Dabrowska-Bernstein, Immunoregulatory Role of Thymus, 2019
Marek P. Dabrowski, Barbara K. Dabrowska-Bernstein
The age-related thymic atrophy comprises progressive substitution of the organ parenchyma with adipose tissue and resulting reduction of epithelial cells, Hassals’ corpuscules, and thymocyte compartment.299,300,307 G. Tridente emphasizes two important aspects of the age-related process of thymic involution.307 The first of them is the fact that the adipose tissue does not simply infiltrate the thymic parenchyma, but rather grows up within the septa, changing progressively the septal/parenchymal ratio. In the contracted thymic parenchyma there remain, therefore, some islets with an unchanged architecture which can be found even in the elderly individuals. The second aspect relates to the repeated stress episodes, which, occurring during life, may accelerate the thymic involution. This factor, being individually different, seems to be mostly responsible for a considerable range of the thymic time-persistence. In addition, it is difficult to estimate the figures of the normal age-related decrease of thymic size in man, since the histological material is routinely obtained from autopsy or from the patients who have undergone cardiac surgery, both the events obviously representing distinct elements of stress.
Thymus variants on imaging of patients with primary Sjögren’s syndrome and polymyositis/dermatomyositis: clinical and immunological significance
Published in Immunological Medicine, 2023
Okinori Murata, Katsuya Suzuki, Tsutomu Takeuchi
In this study, we showed that the prevalence of thymic enlargement and thymus attenuation score was higher in pSS and PM/DM patients than in the general populations examined in previous reports [5,6,15,16]. Thymic enlargement was significantly associated with titres of serum RF in PM/DM patients. Although the significance of serum RF titre in the pathogenesis of PM/DM remains unclear, high titres may reflect immunological activity, as is seen in RA patients. In addition, thymus attenuation score was significantly associated with titre of serum IgG. In general, high titres of IgG often reflect abnormalities of cytokines such as TNF, IL-1β and IL-23, suggesting an abnormal immune response. Thymic involution occurred according to age. In a previous study of healthy individuals, a four-point scale visual assessment of the thymus negatively correlated with participant age [5]. A total of 74% of participants, whose mean age was 58.9 years, demonstrated a completely fatty thymus (Score 0) [5]. On the other hand, in our study, the mean age of PM/DM patients with a thymus attenuation score ≥ 2 was 48.1 years. Therefore, the statistical analysis may have significantly differed due to incomplete thymic involution with age. In this regard, healthy female controls showed less thymic involution compared with men from 40 to 69 years of age [5].
An immunologist’s guide to immunosenescence and its treatment
Published in Expert Review of Clinical Immunology, 2022
Calogero Caruso, Mattia Emanuela Ligotti, Giulia Accardi, Anna Aiello, Giuseppina Candore
This profound and complex change in innate and acquired immunity is probably the result of epigenetic and metabolic modifications affecting immune cells at different levels, from HSCs to terminally differentiated cells. In younger people, HSCs provide a balanced output of myeloid and lymphoid progenitor cells. The shift from lymphoid to myeloid differentiation that occurs with aging determines a bias of aged HSCs toward differentiation into common myeloid progenitor cells and a concomitant reduction in common lymphoid progenitor cell [CLP] frequencies; this is followed by a reduction in B and T cell production with aging [54]. The reduction of naïve T lymphocytes is further linked to thymic involution. It is not completely clear why thymic involution occurs, but it is believed to be an evolutionary reason. In fact, at puberty individuals have encountered almost all pathogens living in their environment and continuing to educate T lymphocytes for cells that will never be of any use would be a waste of energy. After puberty, exposure to new pathogens is, indeed, less likely, and immune memory for local pathogens is critical. Resources are concentrated on maintaining defense against environmental pathogens because immune memory can be very long-lasting [55,56].
Hormone replacement therapy in children with growth hormone deficiency: impact on immune profile
Published in Archives of Physiology and Biochemistry, 2021
Javier Caballero-Villarraso, Rocío Aguado, M. Dolores Cañete, Lourdes Roldán, Ramón Cañete, Manuel Santamaría
Studies of animals (Foster et al. 2000, Brown et al. 2004) and humans (Napolitano et al. 2008) have demonstrated that thymic involution may be pharmacologically reversed. These results are promising for the development of future treatments for HIV-infected patients, as a complement to antiretroviral therapy (Hansen et al. 2009).