HIV-1 Exploitation of Dendritic Cell Functionality and Initial Responses in Mucosal Tissues : Elucidation of Influence of HIV-1 Complement Opsonization, and HIV-1-HSV-2 Co-infection

Sammanfattning: Human immunodeficiency virus (HIV)-1 is transmitted between individuals via sexual intercourse or via blood products. To date there are 38 million people living with chronic HIV infection and around 1.5 million yearly acquire a new infection. HIV is known to have detrimental effects on the immune system and its cell function and leads to the development of acquired immune deficiency syndrome (AIDS). AIDS is characterized by opportunistic infections often fatal to the individual. Mucosal tissues, which are the main site of HIV-1 infection, consist of a complex network of different cell types building up a barrier against the outside world. In the mucosa there are multiple immune cells and one of them is the dendritic cells (DCs), a professional antigen presenting cell needed for priming of adaptive T cell responses. DCs are rarely productively infected with HIV-1 but the virus can modulate the DC phenotype and function by mere exposure to the virus. There are many factors that influence viral transmission including prevalent inflammatory conditions or infections in the genital tract. For instance, a newly acquired herpes simplex virus-2 (HSV-2) infection increases the risk of transmission at HIV-1 exposure by four times. A vital part of the innate immune defense is the complement system, which consists of proteins found in all body fluids. Normally during complement activation, it leads to lysis of pathogens, but HIV-1 can evade this process. This is achieved by the incorporated complement regulatory proteins in the viral plasma membrane leading to accumulation of opsonizing complement fragments on the HIV-1 particles. Our aim with these studies was to deepen the understanding of the HIV-1 exploitation of DC function and elucidate the initial effects exposure and establishment of HIV-1 infection has on the mucosal tissues and immune cells. In addition, we aimed to elucidate the effects HSV-2 exerts on the HIV-1-infection of DCs and how viral complement opsonization affects the viral infection and activation of immune responses. In Paper I we found that coinfection of monocyte derived DCs (MDDCs) with HIV-1 and HSV-2 decreases the amount of the HIV-1 restriction factors SAMHD1 and TREX1 in MDDCs, leading to increased productive HIV-1 infection. In Paper II and III we found that HIV-1 utilizes the complement system to induce higher productive infection of the colorectal and cervical mucosal DCs. The different forms of HIV, free or complement opsonized, had distinct effects on the immune responses and T cell phenotypes in the tissues, all in favor of HIV-1 establishment and productive infection. In Paper IV, HIV-1 exposed DCs triggered after crosstalk with suppressive T cells a prolonged type I interferon response and an upregulation of coinhibitory molecules on the DCs. The findings in this thesis add to the knowledge of HIV-1 early transmission events, how co-infection modulates DC function, and how the presence of HIV-1 affects the priming of adaptive immune responses.