Sleep restriction alters the temporal expression of major histocompatibility complex class II molecules in murine lymphoid tissues

Abstract

Inadequate sleep is a major health concern of modern societies in view of the increased morbidity and mortality rates from physiological disturbances, including compromised adaptive immune responses. Many studies investigated the effect sleep restriction (SR) on the normal immune response in terms of leukocyte number and circulating cytokine and T helper cell (Th) profiles, but none considered the major histocompatibility complex (MHC), namely class II molecules. As no information exists about the normal temporal expression of MHC class II, the present study aimed at understanding how SR affects the adaptive immune response via altering the 1) normal daily expression profile and 2) overall constitutive levels of murine MHC class II by leukocytes' isolates from spleen and axillary lymph nodes. Male C57BL/6 mice were acclimatized to 12:12 light/dark cycle (lights on at 0700, corresponding to Zeitgeber time (ZT) 0) for a week before splitting into 2 groups: control (C) and SR (exposed to a 12 and 18 h of activity, respectively). SR was carried for one week before lymphoid tissues from both C and SR mice were sampled at the following time points: ZT0, ZT5, ZT10, ZT13, and ZT18. Spleen and lymph node cells were assessed for leukocyte number and MHC class II expression at the preselected time points using flow cytometry. SR resulted in a 21% decrease in granulocyte and 24% increase in agranulocyte numbers. MHC class II expression in both lymphoid tissues of C mice varied synchronously across the preselected times of day; they were relatively high just prior to activity onset and later in this period. Comparatively, the diurnal protein profile was altered in both lymphoid tissues of SR: 1) the rise of MHC class II expression during the rest period occurred 4-5 hours earlier and 2) the cyclical pattern during the activity period was blunted and protein expression was maintained at relatively high levels. MHC class II expression was higher in the lymph nodes and lower in the spleen of SR than C, though these differences did not reach statistical significance. In SR; however, the average protein level was significantly higher in lymph nodes than spleen (376.0 + 184.9 vs 188.6 + 42.2, respectively; p = .002) and higher in the granulocytes relative to agranulocytes. Our findings provide empirical evidence of a constitutive diurnal expression pattern for MHC class II molecules that is prone to upregulation upon SR, namely in lymph nodes, and specifically expressed by granulocytes. We speculate that, in mice, chronic sleep deprivation would further dysregulate MHC class II expression that might result in aberrant T cell activation with probable immune-associated pathological diseases such as allergies, autoimmunity, and tumors.

Keywords: C57BL/6 mice; Circadian rhythms; Immune system; Leukocytes; Major histocompatibility complex; Sleep insufficiency.