Coinfection with HIV-1 and HCV--a one-two punch

Abstract

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, cirrhosis, and death; it is estimated that 180 million persons are infected with HCV worldwide. The consequences of HCV are worse in those who are coinfected with human immunodeficiency virus 1 (HIV-1), which is unfortunately a common scenario because of shared risk factors of the viruses. More studies into effects of HCV/HIV-1 coinfection are needed, but efforts have been hampered by limitations in our understanding of the combined pathogenesis of the 2 viruses. Gaining insight into the mechanisms that underlie the immunopathogenesis of these persistent viral infections could lead to new therapeutic strategies for patients with HCV/HIV-1 coinfection.

Figure 1

Schematic representation of the outcomes of HIV-1 and HCV infection. Persistent viruses such as HIV-1 and HCV achieve high levels of chronic viral replication. The ultimate outcomes of HIV-1 and HCV infection depend on host-viral interactions. (A) After initial HIV-1 infection, the viral set point can vary considerably and is related to the ultimate speed of progression to AIDS. About 5%–15% of individuals experience slow progression, while a very small subset of individuals are termed “elite controllers” of HIV-1. (B) After HCV infection, a subset is able to control the virus over a sustained period, termed “spontaneous clearance” or “spontaneous control,” but the majority (~50%– 80%) progress to chronic viremia.

Figure 2

Influence of the order of infection promoting the persistence of HCV in the setting of HIV-1 coinfection. Uninfected individuals are represented in gray, HCV antibody–positive individuals in blue, HIV-1 antibody–positive individuals in red, and dually HCV/ HIV-1 antibody–positive individuals in purple. (A) Most blood-borne exposures result in HCV infection well before HIV-1. The usual outcome is chronicity, represented in the first line. HCV titers become progressively higher after HIV-1 seroconversion. The second line represents the situation where protective immunity is generated. Progressive HIV-1 infection, signified by progressive CD4 T-cell dysfunction and depletion, may abrogate this protective immunity. When rechallenged with HCV, the likely outcome is chronicity. The third line represents a situation where HCV is cleared and HIV-1 is never contracted, and thus protective immunity is preserved. (B) When HIV-1 precedes HCV infection, the generation of protective immunity may be primarily impaired, thus resulting in a greater likelihood of persistent outcome. Together, this schematic may help to explain why there are higher persistence rates in coinfected individuals compared with mono-infected individuals.

Figure 3

Influence of HIV-1 replication and its treatment on the liver in HCV coinfection. The red arrows represent the “vicious cycle” of immune activation and CD4 activation, infection, and depletion, as well as effects on the gut mucosa promoting microbial translocation that are proposed to be central to the immunopathogenesis on the liver. These may affect liver fibrosis by a variety of mechanisms. Treatment of HIV-1 by antiretroviral therapy may interrupt the above processes but may introduce additional issues that are on balance negative to liver disease.

Figure 4

Loss of mucosal lymphoid tissue related to HIV-1 infection could promote HCV-related disease. A recent study in GASTROENTEROLOGY highlights the potential role of bacterial translocation in promoting liver disease, perhaps by direct effects of LPS or indirectly by enhancing immune activation. In addition, the loss of mucosal integrity can be hypothesized to enhance permucosal transmission of HCV in cases of sexual transmission, as has been detected among sexual networks in Europe. Adapted with permission from Balagopal et al.