PERSISTENT T-LYMPHOCYTE RHYTHMS DESPITE SUPPRESSED CIRCADIAN CLOCK OUTPUTS IN RATS

Circadian rhythms in circulating leukocyte and lymphocyte counts persi sted with halved amplitudes in constant light (LL) of 300 Ix intensity for 8 wk, whereas circadian rhythms in body temperature, locomotor ac tivity, and plasma catecholamines were completely suppressed. Subseque nt exposure to constant darkness (DD) normalized all circadian rhythms within 2 wk. Rhythms in circulating T lymphocyte subsets were studied in LL or DD using double labeling with monoclonal antibodies and flow cytometry. Circadian rhythms were suppressed for leukocytes and lymph ocytes but were maintained for both T helper cells (Th) and T cytotoxi c cells (Ts) lymphocytes after 11 wk in LL. A group 24-h rhythm was on ly validated for total lymphocytes after 16 wk in LL. However, individ ual total, Th, and Ts lymphocytes maintained their usual respective ph ase relationships in each rat. The alteration of immune cell circulato ry rhythms likely stemmed from a progressive loss of circadian synchro nization among rats kept in LL. Conversely, after 11 or 16 wk in DD, l eukocytes and lymphocyte subsets circadian rhythms were maintained. Th us catecholamines do not drive circulatory T cell rhythms. The loss of coupling between T lymphocyte rhythms and three major outputs of the circadian system further supports the hypothesis of an independent imm unologic oscillator.