It is possible that the envelope (E) protein 2 of the HCV virion specifically binds to the human CD81 molecule altering the cellular activities in B- and T-cells [7], and it might activate a predominant type-2 immune response contributing to liver inflammation, impaired type-1 immune responses and recurrent flares of type-2 immunity associated with chronic infection [8,9]. Moreover, Meroni et al. [10] have reported that CD81 levels in CD4 T-cells were significantly lower in HIV-infected patients than in healthy controls. It might impair the type-1 response that is required for an adequate immune response against viruses [11]. In lymphocytes, CD81 plays a role in cell activation by lowering the threshold

of cell activation and promoting cell proliferation [12]. CD81-mediated activation of B-cells could promote polyclonal proliferation of naïve FK228 nmr B-cells and play a part

in the development of HCV-associated B-cells disorders [13]. In T-cells, CD81 functions as a co-stimulatory signal which creates a proliferation of T-cells independent of CD28 [14]. Recombinant forms of CD81 and CD81-specific antibodies inhibit infectivity after viral adsorption onto the target cell, suggesting that CD81 does not confer ability of the virus to attach but instead acts as a co-receptor during the internalization process [15,16]. Moreover, CD81 facilitates B-cell–T-cell interaction in the process of antigen presentation [12,17]. In HCV mono-infected patients, it has been reported that Gemcitabine CD81 expression in peripheral blood correlated with the HCV-RNA viral load and that a down-regulation of CD81 was associated with 17-AAG mouse a decrease in the HCV-RNA viral load in patients treated with interferon (IFN)-α [18–21]. However, there is little information for HIV/HCV coinfected patients. The aim of the present study was to quantify CD81 expression in peripheral blood B- and T-cells of HIV/HCV coinfected patients and healthy subjects to examine its association with several virological characteristics and the therapeutic responsiveness to HCV antiviral treatment. We carried out a cross-sectional study on

122 HIV/HCV coinfected patients of the Hospital Gregorio Marañón in Madrid, Spain between January 2005 and September 2007. In addition, we carried out a longitudinal study on 24 out of 122 patients who started HCV antiviral treatment. Twenty HIV seronegative subjects participated as healthy controls. The inclusion criteria were: documented HIV and HCV infections, no prior HCV antiviral treatment, availability of a fresh blood sample, no clinical evidence of hepatic failure, detectable HCV-RNA by polymerase chain reaction (PCR), negative for hepatitis B surface antigen, stable antiretroviral therapy or no need for antiretroviral therapy. The exclusion criteria were absence of diabetes, active opportunistic infections and active drug or alcohol addiction. All work was conducted in accordance with the Declaration of Helsinki.