Importance of residual thymopoiesis in aged adults

Sep 22 2009

Doctor Manuel Leal is managing the Experimental Immune Virology Laboratory (in Virgen del Rocío University Hospital and Instituto de Biomedicina de Sevilla (IBIS), where clinic and basic science researchers work) where he leads a project to establish the functional nature of the thymus gland in adults. So far, it has been proven that this gland keeps on producing lymphocytes in the old age (Ferrando-Martínez et al. AGE, in press), which is a novelty because until very recently it was considered that this organ lost its immune capacity after the puberty. At the same time, the researchers, in collaboration with the Dr. Antonio Ordoñez from the Hospital Cardiovascular Surgery Service, have developed a successful method to obtain thymus samples in vivo from patients subjected to heart surgery. These are the results of a project of excellence of the Andalusian Ministry of Innovation, funded with 197,299 euros.

The thymus is a gland with an important role in the sexual development and maturing of the lymphatic system, which starts its function in the foetus. After the puberty, this organ appears to gradually reduce its size and up to now, it was believed that it stopped working. Moreover, there is a process called immunosenescence that is the ageing of our immune system, which undergoes a loss of its capacity of response to diseases and vaccines. This phenomenon is linked to a higher number of infections in people and it is believed that it can affect the development of cancer or autoimmune diseases. An important aspect of the research led by Manuel Leal is that the thymic function in adults is very heterogeneous and is related to the ageing of the immune system.

'With this discovery, we have proven the importance of residual thymopoiesis (the function of the thymus gland to produce T-lymphocytes) in aged adults by means of a direct quantification of the thymic function', Leal said. We have specifically worked with 65 people with an average of 68.5 years of age, who have taken a sample of thymic tissue that was analysed later. As the thymus gland is placed just behind the breastbone and it is very difficult to get to it, rests of in vivo thymus gland have been used for this research for the first time ever. Until now, only ex vivo glands had been used, after the death of patients or in lab animals.

'We have used the percentage of double positive thymocytes (CD4 and CD8) as the marker of the thymic activity as well as the quantification of DNA rest bearer cells that come from the arranging of genes (TRECs). Both of them are direct markers of the degree of thymopoiesis', Leal pointed out. Another discovery is the direct relationship between the degree of the thymic function and the number of virgin T-lymphocytes in peripheral blood, which refers to the blood that flows all over the body, indicating that the function of the gland is directly related to the T-lymphocytes homeostasis (constant concentration of blood).

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