CIRCANNUAL VARIATION IN LYMPHOCYTE SUBSETS, REVISITED

Background: Circadian and circannual variations in lymphocyte subsets, especially CD8+ T-lymphocytes, have been reported. This study focuses on CD4+ T-lymphocyte seasonal variation over a 6-year 8-month period. Study Design and Methods: Lymphocyte subsets were quantitated monthly for four healthy individuals from 1986 through 1992 as part of a flow cytometry quality-control program. Results: In general, there were no significant seasonal changes in the total number of white cells or in total lymphocyte counts. The absolute numbers of CD4+ T-lymphocytes were lowest in summer when the CD8+ T-lymphocytes were highest. Mean CD4+ T-lymphocyte counts were 846, 967, 618, and 695 per mu L for Subjects 1 through 4, respectively, in winter and 432, 670, 355, and 766 per mu L, respectively, in summer. Two healthy subjects had CD4+ T-lymphocyte counts lower than 300 per mu L on one or more occasions during the study period. In three of the four subjects, the percentage of B-lymphocytes In winter was almost double that in summer. In one of the four subjects, no circannual rhythm was observed in these lymphocyte subpopulations. Conclusion: The seasonal variation in CD4+ T-lymphocyte counts demonstrated in three healthy individuals over almost 7 years is again of interest in light of renewed consideration of using surrogate tests, such as CD4+ T-lymphocyte counts, to screen for AIDS-like diseases that may be in the blood supply.