Hepatitis C virus (HCV) infects approximately 170 million people worldwide and is the leading indication of liver transplantation in the United States. HCV is primarily a blood-borne infection, and heterosexual transmission is rare. However, acute HCV infection is increasingly being reported among HIV-positive men who have sex with men (MSM) with no risk factors for parenteral HCV transmission, suggestive of a possible mucosal route of infection in these individuals. While it is possible that HCV may be transmitted into the bloodstream via mucosal tears induced by sexual activity, is also possible that a mucosal immune defect predisposes HIV+ persons to mucosal HCV transmission. Our pilot study aims to study gut B cells in HCV+HIV+, HCV+HIV-, HCV-HIV+, and HCV-HIV- volunteers. Volunteers will undergo a screening blood draw and flexible sigmoidoscopy with biopsy. We will isolate peripheral and mucosal mononuclear cells and we will perform HCV-specific ELISPOT and single B cell immunoglobulin (Ig) RT-PCR to assess volunteers' gut B cell repertoire. If successful, we would like to expand the study so as to better assess Ig repertoire differences among HCV+HIV+ and HCV+HIV- individuals.