Impact of growth hormone (GH) deficiency and GH replacement upon thymus function in adult patients.
Level 3 - non-randomized controlled study
Prospective single-arm withdrawal-and-rechallenge cohort study without an external control group.
PubMed 19479077 · doi:10.1371/journal.pone.0005668
What was done
Thymic function was evaluated in 22 adult patients with documented growth hormone deficiency (AGHD) receiving maintenance growth hormone (GH) replacement. Plasma IGF-1 concentrations, signal-joint T-cell receptor excision circle (sjTREC) frequency, and sj/beta TREC ratio (measuring intrathymic T-cell proliferation) were assessed at three time points: on maintenance GH, 1 month after GH withdrawal, and 1 month after GH resumption.
What was found
One month after GH withdrawal, both plasma IGF-1 levels and sjTREC frequency decreased significantly (p < 0.001), and these decreases were correlated (r = 0.61, p < 0.01). Intrathymic T-cell proliferation also declined, as shown by a decreased sj/beta TREC ratio (p < 0.01). Following 1 month of GH resumption, IGF-1 and sjTREC frequency returned to baseline levels, while the sj/beta TREC ratio increased but did not fully recover to pre-withdrawal levels. Exact baseline and post-treatment numerical values were not provided in the abstract.
Why it matters
This study provides evidence in adult humans that the somatotrope GH/IGF-1 axis is directly involved in maintaining adult thymic function and T-cell output.
Limits
The study is limited by a small sample size (n = 22), lack of a parallel control group, short 1-month observation windows, and relying entirely on circulating surrogate markers without measuring clinical immune endpoints.
Cited by
- supports The human thymus grows from birth until puberty under the influence of hormones like melatonin, growth hormone, and DHEA, and undergoes involution after puberty.