Strain differences in some immune parameters can be obscured by circadian variations and laboratory routines: studies of male C57BL/6J, Balb/c and CB6F1 mice

This is a report on the potential influence of circadian changes and laboratory routines on some immune parameters (thymic and splenic weights, the numbers of bone marrow, peripheral blood, and peritoneal leukocytes) in: (1) males of C57BL/6J, Balb/c, and CB6 F1 mice kept under identical laboratory conditions; (2) males of CB6 mice kept under the same laboratory conditions, except for opposite light/dark regimes, either light/dark (LD) or dark/light (DL). All the animals were purchased from the same supplier and adapted for 4-5 weeks to strictly controlled housing conditions. Some parameters were similar at certain time points but statistically significantly different at others due to strain-specific daily variations. In order to make the interstrain comparisons more reliable, the data collected around the day/night cycle were pooled for calculations of mean values. Several immune parameters of CB6 mice kept under DL conditions were significantly different than those in mice under the conventional LD conditions. In conclusion, the extrapolation of results (especially in the field of neuroimmunology) to other strains (or species) should, be done with great caution; and all interstrain (interspecific) comparisons, especially those from various laboratories, should always be related to specific time points and laboratory conditions.