SPP1 and multiple sclerosis: The last decade of the 20th century was marked by the discovery of MCP-1/CCL 2, with a role in neuroinflammation and blood–brain barrier disruption [88], the discovery of osteopontin, with early studies of elevated CSF/serum osteopontin levels in multiple sclerosis [89], and the description of neurofilament light chains, which only gained interest later on, with the early studies being limited by assay sensitivity.