TNF and viral respiratory tract infection: Indeed, the role of viral respiratory tract infections in increasing the risk of MS relapses [26,27,28,29] is widely recognized, especially considering that following a viral infection the activation of proinflammatory patterns, such as the host’s T-cells, proinflammatory cytokines, and tumor necrosis factor (TNF)-α, increases the blood-brain barrier (BBB) permeability, allowing for transmigration of those molecules and promoting central nervous system inflammation [30].