A number of age-related changes in the 24-hour hormonal and non-hormonal rhythms have been found in older human beings. Lymphocyte subpopulations present circadian variation of some of their subsets and this variation may influence magnitude and expression of the immune responses. Numerous interactions exist among the nervous, endocrine and immune systems, mediated by neurotransmitters, hormones and cytokines. The aim of this study is to evaluate circadian variations of some endocrine and immune factors in older adults.

Cortisol and melatonin serum levels were measured and lymphocyte subpopulation analyses were performed on blood samples collected every four hours for 24 hours from ten healthy young and middle-aged subjects and from ten healthy elderly subjects. There was a statistically significant difference between the groups in the observed values of CD20 (higher in young and middle-aged subjects) and CD25 and DR+ T cells (higher in elderly subjects). In the group of young and middle-aged subjects a clear circadian rhythm was validated for the time-qualified changes of all the factors studied. In the group of elderly subjects a number of rhythms were absent or altered.

The results of the current study show that aging is associated with enhanced responsiveness of T cell compartment and alterations of circadian rhythmicity. In the other study scientists also performed measurements of cortisol and melatonin serum levels; although lymphocyte subpopulation analyses were performed on blood samples collected every 4 hours for 24 hours from 15 healthy young-middle-aged subjects (range 36-55 years, mean age ± standard error [SE] 44.08± 1.76) and 15 healthy old-aged subjects (range 67-79 years, mean age ± SE 68.52 ± 1.27). Statistically significant difference between the groups in the observed values of CD20 (total B cells higher in young-middle-aged subjects, P = 0.02), CD25 (activated T cells with expression of the alpha-chain of interleukin-2 receptor, higher in elderly subjects, P = 0.04) and DR(+) T cells (activated T cells higher in elderly subjects, P = 0.01) was found. There were different correlations among lymphocyte subpopulations and hormone serum levels in young and middle-aged subjects in compared to old-aged subjects. In the group of young-middle-aged subjects, a clear circadian rhythm was validated for the time-qualified changes of all the factors studied. In the group of elderly subjects, a clear circadian rhythm was validated for the nyctohemeral changes of CD3 (with a phase delay of 3 hours), CD8, CD4/CD8 ratio, CD16, CD25 (in opposite phase), cortisol (with a phase delay of 1 hour) and melatonin.

The results of the current study show that aging is associated with enhanced responsiveness of the T-cell compartment, impairment of B-cell compartment and alterations in temporal architecture and correlations of neuroendocrine-immune parameters.