Interferon-γ induced increases in intracellular calcium in T lymphocytes from patients with multiple sclerosis precede clinical exacerbations and detection of active lesions on MRI

Abstract

Background - Interferon (IFN)-γ exerts a multiplicity of actions potentially relevant for the pathogenesis of multiple sclerosis, including the expression of a transplasmalemma calcium (Ca2+) influx leading to an intracellular Ca2+ ([Ca2+](i)) increase able to lower T lymphocyte threshold of excitability. It has been previously shown in a cross sectional cumulative study that this influx is associated with clinical and MRI evidence of disease activity. Methods - To evaluate the temporal relation between disease activity and the IFN-γ activated Ca2+ influx in individual patients, a fluorimetric analysis was performed on peripheral blood lymphocytes from eight patients with relapsing-remitting multiple sclerosis every 15 days for one year. Results - Fluctuations of the influx were correlated with clinical events and monthly enhanced brain MRI. The influx was detected a mean of 10.4 (range 7-17) times per patient during our analysis. In 61% of the occasions, influx induced [Ca2+](i) increases were recorded in each patient in more than two consecutive measurements, determining sustained [Ca2+](i) increases lasting for a mean of 31.5 days. Peak [Ca2+](i) increases preceded clinical attacks (P = 0.04) or maximal detection of brain MRI enhancing lesions (P = 0.05) by a mean of 30.8 and 34.2 days respectively. Spectral analysis of time series further indicated that the fluctuation frequency of [Ca2+](i) increases due to the influx over time were superimposable on the appearance of new MRI lesions in all patients and confirmed that in two thirds of the patients these [Ca2+](i) increases occurred significantly before (P < 0.005) or concurred with new lesion appearance. Finally, the overall presence of the influx throughout the follow up period correlated (P = 0.03) with the patients' exacerbation rates. Conclusions - Intracellular events leading to T lymphocyte activation in multiple sclerosis occur in the peripheral blood before CNS specific events become evident and are, in part, sustained by cytokine induced Ca2+ mediated phenomena.