Worldwide, the heterosexual route is the most common mode of sexual transmission of HIV-1 and women are particularly susceptible to this infection. After penetration of the mucosal epithelium HIV-1 interacts with potential target cells, i.e. dendritic cells (DCs) and CD4+ T cells. The complement system, a key component of the innate immune system, is immediately activated by HIV-1 in vivo. However, HIV-1 can resist complement mediated lysis and become coated with complement fragments and this opsonization influences the viral interaction with immune cells. The DCs are the most potent antigen presenting cell. This cell effectively links the innate recognition of viruses to the generation of an adaptive immune response. However, HIV-1 exploits the function of the DCs to facilitate viral spread and infection. HIV-1 interacts with a range of receptors expressed by the DCs including C-type lectins, integrins and complement receptors (CRs). The uptake of virions by DCs leads to their activation and migration to the lymph nodes. At this site DCs present HIV-1 derived antigen on MHC class I and II molecules and trigger an HIV-1 specific T cell response. The interplay between the virus and the DCs is complex and the initial receptor binding may affect antigen uptake, infection, and antigen presentation.

The fundamental questions of this thesis are the following: How is free and opsonized HIV-1 internalized, processed, and presented on MHC class I and II molecules by DCs and how do free and opsonized HIV-1 particles interact with immune cells in the cervical mucosa?

Our results indicate that opsonization of HIV-1 plays a critical role in the interaction with immune cells. Complement opsonization of HIV-1 (C-HIV) significantly enhanced the internalization by the DCs compared to free HIV (F-HIV). Both C-HIV and F-HIV interacted with the CD4 receptor, C-type lectins and integrins. In addition, opsonization of HIV-1 favored an MHC class I presentation by DCs compared to F-HIV. However, the endocytic receptors macrophage mannose receptor, β7 integrin, and CR3 guided the antigens to different compartments with distinct properties and efficiencies for degradation and MHC class I and II presentation of viral antigens. MHC class I presentation of F-HIV and C-HIV was dependent of viral fusion in a CD4/coreceptor dependent manner. Moreover, MHC class II presentation of antigens derived from HIV-1 required endocytosis and proteolysis in acidified compartments. HIV-1 infection of cervical mucosa immune cells and tissue was assessed in a cervical tissue explant model. C-HIV significantly enhanced infection of DCs compared to F-HIV, whereas C-HIV decreased the infection of CD4+ T cells. Blocking the viral use of integrins in the cervical tissue explants significantly decreased the HIV-1 infection of both emigrating DCs and CD4+ T cells and the establishment of founder populations in these tissues. This thesis work has brought forward new facts that can be used to facilitate the development of an effective vaccine or microbicide.