Peripheral Blood B Cell Subset Skewing Is Associated with Altered Cell Cycling and Intrinsic Resistance to Apoptosis and Reflects a State of Immune Activation in Chronic Hepatitis C Virus Infection

Chronic hepatitis C virus (HCV) infection is associated with B cell activation, although underlying mechanisms are unclear. To investigate B cell regulation during HCV infection, we measured bulk B cell CpG and Staphylococcus aureus Cowan-induced IgG Ab-secreting cell (ASC) frequency, HCV and tetanus-specific ASC frequency, BCR- and CD40L-dependent CD80/CD86 expression, and activation of memory CD4 cells. Immature transitional, naive, resting memory, mature activated, tissue-like memory, and plasma B cell subset frequencies, cell cycling, and intrinsic apoptosis were quantified. We observed intact or enhanced tetanus-specific and total IgG ASC frequency, serum IgG, BCR- and CD40L-dependent CD80/CD86 expression, and CD40L-dependent bulk B cell activation of memory CD4 cells in HCV infection. HCV-specific ASCs were observed in HCV-infected but not control subjects, although frequencies were lower compared with tetanus-specific cells. Immature transitional and mature activated B cell subset frequencies were increased in HCV-infected subjects, with immature transitional frequency associated with liver inflammation and serum B cell-activating factor. Mature activated B cells less commonly expressed Ki67, more commonly expressed Bcl2, and were more intrinsically resistant to apoptosis, whereas immature transitional B cells more commonly expressed Ki67, the latter associated with plasma HCV level. Taken together, these results indicate that in the setting of chronic HCV infection, a state of activation results in B cell subset skewing that is likely the result of alterations in homeostasis, cell cycling, and intrinsic resistance to apoptosis and that results in an overall intact or enhanced B cell response to BCR and CD40L. The Journal of Immunology, 2010, 185: 3019-3027.