Serum BAFF level is positively correlated with immature transitional and naive B cell frequency and negatively correlated with resting memory B cell subset frequency. Serum BAFF level was measured by ELISA, and results comparing HCV-infected and healthy control subjects are shown in A, whereas results comparing BAFF level to peripheral B cell subset frequency were immature transitional (B), naive (C), resting memory (D), mature activated (E), tissue-like memory (F), and plasma cells (G).