Based upon the combined observations that 1) HCV progression is faster in HIV co-infection; 2) this effect is not necessarily solely due to immunodeficiency; and 3) TRAIL dysregulation characterizes both HIV disease and HCV liver injury, we hypothesized that the ability of HIV to modulate TRAIL signaling in T cells might also occur in hepatocytes. The gene discussed is TNFSF10; the disease is immunodeficiency disease.