A recent PLoS One study by Gabriel Morrhaye et al., demonstrates that the functional integrity of the somatotrope growth hormone/insulin-like growth factor-1 axis is important for the maintenance of a normal thymus function in human adults.
The secretion of growth hormone (GH) declines with aging until only low levels can be detected in individuals aged ≥60 years. Recent evidence also indicates that infusion in old mice of ghrelin, a GH secretagogue, significantly improves thymopoiesis, whereas GH treatment may reverse thymic atrophy and enhance the number of circulating naive CD4 T cells in HIV-infected adults.
The PLoS One study shows that, in patients with well-documented GH deficiency, both the frequency of circulating sjTRECs (marker of thymic T cell output) in PBMCs and the sj/bTREC ratio (marker of intrathymic precursor T cell proliferation) are significantly decreased one month after GH withdrawal.
Resumption of GH treatment for one month is sufficient to increase thymic T cell output to a level similar or close to the one measured before GH interruption.
The authors suggest that the use of GH and/or GH secretagogues should be considered in the future for restoring an important set of thymic functions that are compromised by aging.