Seasonal variation in immune measurements and MRI markers of disease activity in MS

Background: The exact mechanisms by which T cells contribute to MS progression are not known. Recently, the results of cross-sectional studies suggested seasonal variation of both interferon (IFN)-gamma production and the number of active MRI lesions in MS. Objective: To investigate whether seasonal fluctuations of IFN-gamma and active MRI lesions could be confirmed and whether any correlations could be detected. Methods: Data were analyzed from a group of 28 MS patients in whom detailed longitudinal monitoring of both immune function and MRI measurements had taken place. Results: Significant seasonal variation was observed in T-cell activation as measured by the ability of T cells to secrete the pro-inflammatory cytokines tumor necrosis factor-alpha and IFN-gamma. Maximum values were found in samples obtained during autumn. Even though clear fluctuations were observed, no significant seasonal variation could be detected in the number of active MRI lesions. Fluctuations of in vitro IFN-gamma secretion correlated weakly with changes in active MRI lesions. Conclusion: The finding of seasonal variation of immune function in serially MRI-monitored MS patients suggests an environmental role in T-cell activation.