Hypovitaminosis D upscales B-cell immunoreactivity in multiple sclerosis

Background: While vitamin D is increasingly recognized as a potential immune regulator of MS disease activity, its impact on B lymphocytes, however, remains ill-defined. Methods: We assessed the impact of vitamin D on B-cell proliferation and cytokine secretion ex vivo and screened for effects of hypovitaminosis D and vitamin D supplementation on the compartmentalized distribution of B-cell subtypes in peripheral blood and cerebrospinal fluid (CSF) from patients with relapsing remitting MS (n = 95) and various neurologic and healthy controls (n = 57). Results: B cells from MS patients with 25(OH)D serum levels <20 ng/ml, displayed enhanced immunoreactivity ex vivo as a consequence of more vigorous responses of CD27(+) memory phenotypes. Immune responses decreased when B cells from either source were co-cultured in the presence of vitamin D or when retesting B cells from MS patients after prolonged supplementation with vitamin D. Hypovitaminosis D was detectable in the serum of 40/95 MS patients, correlated with decreased vitamin D concentrations in CSF and with higher disease activity, and was paralleled by intrathecal accumulation of CD27(+) B-cell subtypes and plasma cells. Conclusion: B-cell immunoreactivity is attenuated by vitamin D. Our finding that vitamin D deficiency affects the intrathecal compartment and coincides with increased frequencies of effector B-cell subtypes in the CSF suggests that hypovitaminosis D might contribute to augmenting disease activity in the target organ and supports a potential benefit of vitamin D supplementation in MS. (C) 2016 Elsevier B.V. All rights reserved.