A possible mechanism for altered immune response in the elderly.

BACKGROUND

Reciprocal influences and bidirectional connections among the nervous, endocrine and immune systems, mediated by shared neuroendocrine hormones, chemo/cytokines and binding sites contribute to the maintainment of body homeostasis. The hypothalamus-pituitary axis may play an immunomodulating role and influence cellular immune responses by releasing various hormones and neuropeptides into the blood with direct modulatory action on the immune effectors, or by regulating the hormonal secretion of peripheral endocrine glands. Aging is associated with changes in immune function. The aim of this study was to evaluate circadian variations of some endocrine and immune factors in the elderly.

MATERIALS AND METHODS

Serum levels of cortisol, melatonin, thyrotropin-releasing hormone (TRH), thyroid stimulating hormone (TSH), free thyroxine (FT(4)), growth hormone (GH), insulin-like growth factor (IGF) 1 and interleukin (IL) 2 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 individuals (age 35-54 years) and from ten healthy elderly individuals (age 65-76 years).

RESULTS

There was a statistically significant difference between the groups in the observed values of CD20 and TSH serum levels (higher in the young and middle-aged) and CD25 and DR(+) T-cells (higher in the elderly). 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, with the exception of FT(4), IGF1 and IL2. In the group of elderly individuals, a number of rhythms and correlations with neuroendocrine hormones were absent or altered.

CONCLUSION

The results of the current study evidence aging-associated decrease of peripheral B-cell compartment, increase of activated T-cell compartment, decrease of hypophyseal thyrotropin secretion, altered circadian rhythmicity and altered hormone-immune cell correlations.