Memory (CD27⁺) B cells and progression of HIV infection. (A) Relationship between memory B-cell percentages and CD4⁺ T-cell counts. The relationship between memory B cells and CD4⁺ T cells in 80 subjects with CHI was tested by linear regression. (B) Comparison of memory B-cell percentages at different stages of HIV infection. PBMCs from HIV-negative controls and individuals with PHI or CHI, and LTNP patients were analyzed for percentage of cells staining double positive for CD19 and CD27 (CD19⁺CD27⁺) using fluorescence-activated cell sorter (FACS) analysis. The box plot for LTNP patients represents data pooled from 7 subjects, each sampled twice, with a 7-year interval between samples. (C) IgM⁺IgD⁺CD27⁺ and IgM^-IgD^-CD27⁺ B cells in controls, patients with PHI, and patients with CHI. Expression of IgM and IgD was analyzed in CD19⁺CD27⁺ (memory B cells) from HIV-negative controls and individuals with PHI or CHI.