Treatment for HCV patients with mixed cryoglobulinemia is similar to treatment for HCV patients without cryoglobulinemia, namely pegylated interferon-alfa and ribavirin to reduce viral load. One of the newer treatment option to alleviate symptoms of cryoglobulinemia is rituximab;a drug originally approved for the treatment of Non-Hodgkins lymphoma but is now being trialled as a new treatment option for rheumatoid arthritis, multiple sclerosis and lupus patients. Rituximab is a chimeric murine/human monoclonal antibody directed against the CD20 antigen found on the surface of some immature B cells and all mature B cells except long-lived plasma cells. Binding of Rituximab to CD20 triggers B cell death through direct cell lysis, complement dependent cellular cytotoxicity or antibody dependent cellular cytotoxicity, which is mediated by natural killer cells or macrophages. B cell depletion is complete within the first few months of the start of treatment and is sustained for 6-9 months in 83% of patients. Recovery of B cell numbers commences at 6 months following completion of treatment with median B cell levels returning to normal by 12 months post treatment. The rationale for using this agent to treat HCV-infected patients with mixed cryoglobulinema is that it would deplete the oligoclonal/polyclonal population of B cells that are producing rheumatoid factor and driving this disease whilst having a minimal effect on other populations of immune cells and virus control. During the past year we have initiated studies to investigate changes in the B and T cell compartments of patients with chronic HCV infection in the context of mixed cryoglobulinemia, and the impact of rituximab treatment on immune cell function. Chronically infected HCV patients that have either not received treatment for hepatitis C or have failed treatment are currently enrolled in this study and have contributed peripheral blood mononuclear cell samples prospectively during rituximab treatment. As controls for T and B cell function we study healthy blood donors, and to control for general inflammatory conditions induced by a viral infection of the liver we study hepatitis B virus (HBV) e antigen positive and negative patients. We found an expansion of the activated B cell compartment of hepatitis C patients with mixed cryoglobulinema compared to hepatitis C patients without mixed cryoglobulinemia, HBV patients and healthy controls. This expansion was accompanied by a higher percentage of activated B cells expressing BAFF receptor as well as higher total expression of BAFF receptor. During rituximab-induced depletion of B cells total CD8 T cell counts remained largely unchanged whereas CD3 T cells, and in particular CD4 T cells, increased transiently but decreased once B cell numbers start to recover. Th17 cells, a newly defined CD4+ T cell subset linked to autoimmune disease, will be studied by staining for IL-17 expression after HCV peptide-specific stimulation with HCV overlapping peptides followed by intracellular cytokine staining and flow cytometry. We hope that these studies will shed light on the mechanisms of B cell dysfunction in hepatitis C and the pathogenesis of HCV-related autoimmunity.