Data regarding: Seasonal variations in macrophages/microglia underlie changes in the mouse model of multiple sclerosis severity
Multiple sclerosis (MS) patients show seasonal variations in relapses, lesion numbers and activity and in several cytokines important for the disease. These variations have been associated with environmental factors, as solar exposure, either during adult life or during perinatal period. Data regarding seasonal variations in the MS animal model, experimental autoimmune encephalomyelitis (EAE), are scarce, but suggest that these variations may be endogenous, since they were detected in animals maintained under a controlled environment. We aim to address the effect of both the season of birth and of EAE induction on EAE severity and on immune pathogenic (Th1, Th17 cells, macrophages/microglia) and protective (T regulatory cells) responses in the central nervous system (CNS). A total of 51 independent experiments in which EAE was induced in C57BL/6 mice maintained under a 12:12 light:dark cycle and controlled conditions of temperature and humidity were retrospectively analyzed. EAE induction protocol and EAE score assessment, and protocols for isolating CNS mononuclear cells and assessing immune subsets cells can be found in Álvarez-Sánchez et al. Brain, Behavior, and Immunity. 2015. Briefly, EAE was induced by s.c. administration of 100 μg of MOG35-55 emulsified in CFA containing 50 μg of heat-killed Mycobacterium tuberculosis (H37Ra), followed by two i.p. doses of 400 ng of pertussis toxin on days 0 and 2. Clinical signs of EAE were assessed as follows: 0: no clinical signs; 1: limp tail; 2: impaired righting reflex; 3: partial hind limb paralysis; 4: complete hind limb paralysis; 5: complete hind limb paralysis + frontal limb paralysis; 6: dead or moribund. CNS (brain + spinal cord) isolated at the peak of disease from EAE mice perfused with cold PBS were digested with 1.25 mg/ml of collagenase IV and 0.5 mg/ml of DNase I for 35 minutes at 37°C, and mononuclear cells were isolated using a 30%:70% discontinuous Percoll gradient. CNS mononuclear cells were cultured at final density of 3x106 cells/ml (RPMI 1640 supplemented with 5% fetal bovine serum, 2 mM L-glutamine and 50 U/ml of penicillin/streptomycin). T effector cells (Th1 and Th17 responses) were studied by flow cytometry on CNS-infiltrating mononuclear cells cultured overnight with MOG 10 μM and incubated with brefeldin A for the last 5 hours of culture. Treg cells and macrophages/microglia were studied in ex-vivo CNS-infiltrating mononuclear cells. Our data show that summer-born or summer-immunized animals developed a milder disease, which coincided with variations in numbers of T effector/Treg subsets, and significantly low count of macrophages/microglia. Moreover, both the season of birth and the season in which EAE was induced were independently associated with EAE susceptibility. These data suggest that endogenous rhythms in immune responses might cause seasonal variations in EAE severity and that they might be related to macrophages/microglia.