Any quantity varying in the spatial-temporal dimension may be considered as a signal. Human lymphocyte cell surface molecules and subsets present circadian variation and this variation may represent a kind of signalling in the neuroendocrine-immune system. We have analyzed the dynamics of variation of specific lymphocyte subsets in healthy humans.

In our study, lymphocyte subpopulation analyses were performed and cortisol, melatonin, GH and TSH serum levels were measured on blood samples collected every 4h for 24hours from eleven healthy men, ages 35–53 years (mean=44±6SD).

A clear circadian rhythm was validated for CD8 and cortisol with acrophase during the day and for CD3, CD4, melatonin, GH and TSH with acrophase at night. Cross-correlation showed that CD3 correlated positively with CD4 (ρ=0.67, P<0.05) and negatively with CD8 (ρ=−0.41, P<0.05), CD4 correlated positively with melatonin (ρ=0.90, P<0.05), GH (ρ=0.92, P<0.05) and TSH (ρ=0.71, P<0.05), negatively with CD8 (ρ=−0.90, P<0.05) and cortisol (ρ=−0.18, P<0.05), CD8 correlated positively with cortisol (ρ=0.38, P<0.05).

The different profiles of nyctohemeral changes of lymphocyte cell surface molecules and specific lymphocyte subsets realize different relationships with the neuroendocrine hormones and might represent a way of signal transmission among the multiple components of the neuroendocrine-immune system.