No correlation between anti–vaccinia virus antibodies and memory B cells in blood. Anti–vaccinia virus IgG titer and anti–vaccinia virus memory B-cell frequency from the same blood samples were compared. Data are from n = 23 individuals including 12 control individuals (circles), 5 splenectomized patients (diamonds), and 6 rituximab-treated patients (triangles) for whom both values were measurable. Dashed symbols correspond to maximum estimates for individuals for whom memory B cells were undetectable (“Memory B-cell assay”) and anti–vaccinia virus serum titer were positive. Shown is the Spearman coefficient of correlation R² for the n = 23 samples (P = .88).