FCGR3A and primary progressive multiple sclerosis: Studies on membrane FCGR3A expression in NK cells in MS have yielded mixed results: some report decreased cytotoxic activity of CD16+ NK cells in RRMS patients, correlating with disease activity (35) while others found no significant differences in the percentages of NK cells expressing or lacking CD16 between untreated RRMS patients and HC (36), or even higher percentages of these NK cells in PPMS and SPMS patients (37).