Circadian changes in human natural killer-cell activity

The circadian changes in natural killer (NK) activity of peripheral blood mononuclear cells (PDM) were studied in five clinically healthy, diurnally active, nocturnally resting women. Data on spontaneous NK-cell activity were complemented by data on the chronosusceptibility to in vitro inhibition by 1 X 10(-6) M cortisol and by the rhythmometric evaluation of rectal temperature and plasma cortisol as potential circadian markers. In April-July, 1985, blood was drawn at 4-hr intervals for 24 hr starting at 0800 hr. Cells were immediately separated and assayed for NK activity using K 562 cultured cells as a target and a 4-hr 51Cr-release assay. Circadian variations of the spontaneous NK activity were apparent; the maximum of the activity occurred in the morning or in the early afternoon. In individual subjects, peak-to-through differences were 50% or more of the 24-hr mean. Chronosusceptibility to cortisol (20 hr incubation prior to the cytotoxic assay) was ecphasic with respect to the spontaneous NK-cell activity, with a maximum in the evening or night. Data obtained by immunofluorescence using specific anti-NK cell monoclonal antibodies confirm the occurrence of a higher number of phenotypically identifiable NK effectors in the morning vs. other circadian stages. Our data confirm previous findings and extend their scope to immunopharmacology emphasizing the need for time-qualified investigations on immune coordination in vivo.