CD27⁺CD21^low, compared with CD27⁺CD21^high, B cells have attenuated Ca²⁺ responses after BCR cross-linking. Analyses of B cells from one healthy volunteer (ECH 503), 2 HCV⁺MC⁻ patients (ECH 530 and ECH 537), and 5 HCV⁺MC⁺ patients (ECH 546, ECH 559, 110, LDU 125, and 1931) are shown. PBMCs from 1931 and LDU 125 were collected 4 and 10 months, respectively, after the cells collected for the microarray and primary immunophenotyping experiments. (Left panels) CD27 and CD21 staining of IgG⁻ B cells. Indo-1-AM-loaded cells were stained with anti-CD19, anti-IgG, anti-CD27, and anti-CD21, warmed to 37°C, and, after establishing a baseline for 30 seconds, stimulated with 10 μg/mL goat F(ab′)₂ anti–human IgM. Kinetic graphs represent ratios of bound/unbound Indo-1 over time for CD27⁺CD21^high, CD27⁺CD21^low, CD27⁻CD21^high, and CD27⁻CD21^low B-cell populations. Single arrows indicate injection of F(ab′)₂ anti–human IgM; and double arrow, injection of 10 μg/mL ionomycin.