Clinical and radiologic correlates of a novel T lymphocyte γ‐interferon‐activated Ca ²⁺ influx in patients with relapsing remitting multiple sclerosis

T lymphocytes are the main cellular mediators in MS pathogenesis, and their activity is modulated by a complex cytokine network in which gamma-interferon (gamma-IFN) is considered essential. We have recently identified a new transplasmalemma Ca2+ influx activated by gamma-IFN in T lymphocytes (mainly CD4+) from patients with MS that makes T cells more susceptible to proliferation. To define the possible role of this Ca2+ influx as a marker of disease activity, we correlated its appearance with clinical and MRI findings in a cross-sectional study of 67 patients with relapsing-remitting MS (RR-MS). We also conducted a short-term longitudinal evaluation (every 15 days over a 5- to 7-month period) in three of the RR-MS patients. Sixty-five percent of all clinically active RR-MS patients showed the gamma-IFN-activated Ca2+ influx. However, positivity was higher in the first week (78%) after the onset of a clinical exacerbation than the second (57%) and third (44%) weeks. The influx was also detected in 45% of clinically stable RR-MS patients, 30% of RR-MS patients with a "benign" course of the disease, 14% of the other active autoimmune or neurologic disease patients, and 9% of healthy subjects (RR-MS versus control subjects, p < 0.001). Brain-MRI gadolinium-enhancing lesions were more frequently found in influx-positive (72%) than in influx-negative (47%) patients (p < 0.005). In the longitudinal study, we recorded five intracellular Ca2+ ([Ca2+]i) elevations and three clinical attacks (one per patient). A peak increase of [Ca2+]i due to the gamma-IFN-activated Ca2+ influx always preceded the clinical attacks from 4 to 45 days and coincided to MRI evidence of inflammation. [Ca2+]i had returned to baseline levels by the time of the onset of two clinical attacks. This finding may account for the lack of detection of the gamma-IFN-activated Ca2+ influx in some RR-MS patients during the first week after clinical onset. The strong association between the influx and clinical and MRI evidence of disease activity supports its role in the early phases of cellular immune activation leading to demyelination in MS. The detection of [Ca2+]i elevations due to the gamma-IFN-activated Ca2+ influx may represent a valuable prognostic marker of disease activity and may be useful to monitor immunologic studies of MS patients in future clinical trials.