CD38 and primary progressive multiple sclerosis: We found an expansion of one population of NK cells with a phenotype suggestive of terminally differentiated mature NK cells (NK-4 or named mNK/CD16high, characterized by CD56+, CD57+, CD16+, CD38+) in PPMS patients with leptomeningeal enhancement (active PPMS) compared to those without (inactive PPMS) (Kruskal Wallis H test, p= 0.027, PPMS active versus inactive; adjusted p-value = p = 0.059) (Figures 6C, D).