(A–H) The absolute number of total lymphocytes and all investigated B cell populations and surface molecules, except CCR5 at 12 months, increases significantly and persistently in patients with multiple sclerosis during natalizumab treatment. (I) The proportion of CD19+CD20+ B cells of all peripheral blood lymphocytes increases in patients with multiple sclerosis already after 1 week of natalizumab treatment. (J) The proportion of CD10+CD19+CD20+ pre–B cells increases already after 1 week of natalizumab treatment. (K) The proportion of CD5+CD19+CD20+ B cells is not altered during natalizumab treatment. (L) The proportion of VLA-4+CD19+ cells decreases already after 1 week of natalizumab treatment. (M) The proportion of CCR5+CD19+ cells is not altered during natalizumab treatment (N) The proportion of CCR6+CD19+ cells is not altered during natalizumab treatment. (O) The proportion of CXCR3+CD19+ cells increased after 1 month of natalizumab treatment. (P) The proportion of CXCR3+CD19+ cells increased in 11 of 13 patients from baseline to 3 months during natalizumab treatment. Median, lower and upper quartiles, and range (A–H) or mean ± standard error (I–O) is shown except (P), where lines represent intraindividual changes.*p < 0.05, **p < 0.01, ***p < 0.001 compared to baseline (0 months). m = month; VLA-4 = very late activation antigen 4; w = week.