HMBG1 and other soluble factors in HIV-1 pathogenesis

Abstract

The innate immune system is the first defense mechanism invading pathogens encounter. Macrophages, dendritic cells and cytokines/chemokines are important factors for the functionality of the innate immunity, and provide the adaptive immune system with sufficient signals for the proper action. Immune activation occurring during HIV-1 infection is essential to understand and investigate.

The aims of this thesis were to evaluate the role of immune activation factors of the innate immune system, such as cytokines and chemokines, in different sets of patient categories, cellular systems and phases during the HIV-1 infection. We were most interested in a particular cytokine, the high mobility group box protein 1 (HMGB1). In addition to our in vitro experiments, we had access to an unique cohort, the Quest study, which is the first placebo controlled treatment trial in acute HIV-1 infection. For our substudy, we selected 22 patients, categorized into responders and non-responders regarding the outcome of their viral load after analytical treatment interruption (ATI). We found that high levels of immune activation as determined by the pattern of cytokines/chemokines during PHI, did not favor a better virological outcome after ATI. The early initiation of ART did not seem to affect the preservation of the immune system.

HMGB1 is a proinflammatory cytokine, ubiquitously expressed in all nucleated cells, with a functional importance as a regulator of transcription and stabilization of the nucleosomal structure. HMGB1 is actively secreted from LPS- or TNF-activated macrophages/monocytes, pituicytes and other cells. HMGB1 can also be passively released by damaged necrotic or apoptotic cells. We studied the role of HGMB1 in different systems and modes during HIV-1 infection. Extracellular HMGB1 upregulated HIV-1 infection in latently infected U1 monocytic cells, but did not have impact on viral replication in ACH-2 Tlymphocytic cells. In acute HIV-1 infected monocyte-derived macrophages (MDMs), HIV-1 production was downregulated, most likely due to the increased production of the chemokines MIP-1alpha, MIP-1beta and Rantes. Furthermore, higher levels of HMGB1 were found in HIV-1 infected patients with deteriorated immune status and opportunistic conditions, compared to uninfected individuals and HIV-1 infected patients with less preserved immune status. Additionally, HMGB1 was released by HIV-1 infected MT4 cells and CD4+ T-cells, in connection with virus induced cell death. This release could be interfered by addition of a pan-caspase inhibitor Z-vad to MT4 cells cultures. We suggest that HMGB1 was released passively from MT4 cells not only during necrosis but also during apoptosis.

In conclusion, the presented data cast a light on the importance of the immune activation process during HIV-1 pathogenesis. HMGB1 is released during the viral cell infection and may be a molecule connecting the cell death processes and the immune activation during HIV-1 infection.