The independent contributions of microbial translocation and liver fibrosis to immune activation in human immunodeficiency virus (HIV) and/or hepatitis C virus (HCV)–infected persons are unclear.

Multivariable linear regression was used to evaluate whether intestinal fatty acid binding protein (I-FABP: a marker of gut epithelial integrity) and transient elastography-measured liver fibrosis might mediate the association of HIV and HCV with the soluble CD14 (sCD14) level in 120 individuals with HIV and HCV coinfection, 262 with HIV monoinfection, 72 with HCV monoinfection, and 170 without infection.

Coinfected individuals, HIV-monoinfected individuals, and HCV-monoinfected individuals had 37%, 21%, and 12% higher sCD14 levels, respectively, than uninfected individuals, after multivariable adjustment. Additional adjustment for I-FABP level modestly attenuated the association of HIV infection, but attenuation occurred to a lesser extent in the HCV-monoinfected group. Adjustment for liver fibrosis substantially attenuated the association of HCV infection, but attenuation occurred to a lesser extent in the HIV-monoinfected group. Relative to the uninfected group, the primary mediator of the sCD14 level was the I-FABP level in the HIV-infected groups and liver fibrosis in the HCV-monoinfected group.

HIV and HCV are independently and additively associated with higher a sCD14 level. Our findings suggest that microbial translocation contributes to an increased sCD14 level during HIV infection, whereas liver fibrosis plays a stronger role during HCV monoinfection. Coinfected persons may be at greatest risk for progression, because of the independent effects of microbial translocation and liver fibrosis on immune activation.