Complement vs.IgG:HIV opsonisation determines DC modulation

It is no surprise that all HIV-1 in vivo isolates tested so far are opsonised, because the virus activates the complement (C) system even in the absence of HIV-specific antibodies. Thus already at initial phases of infection, HIV is coated with complement fragments (C-HIV). During the chronic phase, when HIV-specific IgGs appear, the virus circulates immune-complexed together with IgG and complement (C/IgG-HIV). Recent in vitro experiments in our laboratory revealed that C-coating of HIV-1 enhanced the productive infection of immature dendritic cells (iDCs) when comparised to application of non-opsonised virus. In contrast, HIV-1 opsonised with anti-HIV-1-IgG did not productively infect iDCs independent on the presence of C; this was not due to a neutralising capacity of the antibodies since IgG-coated HIV-1 preparations infected PHA-/IL-2- stimulated CD4 + cells very efficiently. Further differences induced by differentially opsonized virus were observed with respect to MAPK signaling and cytokine secretion in iDCs. While C-HIV triggered the ERK1/2 pathway upon binding to iDCs similar to the positive controls, the signal induced by C/IgG-virus was impaired. In contrast, the IgG-opsonized virus induced the highest levels of IL-10. The opsonisation pattern of HIV-1 may have profound consequences for the outcomes of an adequate immune response since DCs direct nave T cells via their HLA class I- or II-peptide surface complexes into a TH 1- or TH 2- direction. At the beginning of infection, the virus is opsonised with complement fragments only. Under these circumstances, iDCs are productively infected in vitro. In vivo, after seroconversion, when anti-HIV-IgGs have appeared, productively infected DCs are rarely found. Thus the results observed in our preliminary in vitro experiments may reflect the in vivo situation. Therefore, starting from the finding that non- or complement- (C-) opsonised and C- /IgG- or IgG-coated HIV-1 are differentially handled by iDCs, this proposal addresses the putative mechanisms responsible for these phenomena and tries to elucidate the functional consequences concerning signal transduction pathways, cytokine patterns and HLA expression induced by non- or C-opsonised vs. IgG-coated HIV-1. Based on the knowledge that in vivo HIV-1 is differentially opsonised, a detailed understanding of these first steps in HIV infection may help to identify new targets to fight HIV.

During the project `Complement vs. IgG: The way of HIV-opsonisation determines dendritic cell modulation` we identified basic mechanisms taking place during early and late stages of HIV pathogenesis. Upon entry of HIV via mucosal surfaces, the virus activates complement even in the absence of HIV-specific antibodies. Thereby, HIV is opsonised (coated) with complement (C) fragments already at the beginning of infection. After seroconversion, when HIV-specific antibodies are produced, the virus is additionally coated with specific antibodies (IgGs). We found that the different opsonisation patterns of the virus - also detectable in these forms in HIV-infected individuals - exerted a profound impact on the infection and integration of dendritic cells with HIV. Dendritic cells (DCs) represent the most important antigen-presenting cells. In an immature state they sample mucosal surfaces for antigens and following uptake of an antigen they start to mature. Mature DCs migrate to the lymphatic tissues, where they present the captured antigen to nave CD4 and CD8 T cells. We found that dendritic cells were differentially modulated dependent on the opsonisation pattern of HIV. C-opsonised HIV (HIV-C) efficiently integrated in and infected DCs, while no or a significantly impaired infection and integration was observed with Ig- opsonised HIV (HIV-Ig). Additionally, the transfer of the virus to T cells was dependent on the opsonisation pattern of the virus. HIV-C-loaded DCs efficiently transmitted the virus to T cells in short- and long-term experiments, while DCs exposed to HIV-Ig infected T cells only in short-term experiments. To further characterise the differences that were found in DC infection and integration with differentially opsonised HIV preparations we performed microarray analyses in collaboration with the University College London. Also these still on-going analyses revealed significant differences with respect to genetic changes induced by complement- or IgG-opsonised HIV. The most important finding of our project was that the opsonisation pattern of HIV exerts profound consequences for the outcomes of the antigen-presenting capacity of dendritic cells. We could show, that complement acts as an endogenous adjuvant for dendritic cell-mediated induction of HIV-specific cytotoxic lymphocytes. Based on these findings we are now working on the impact of the HIV-opsonisation pattern on the antigen-presenting capacity of dendritic cells within the follow-up project P22165-B13: `Dendritic cells exposed to complement-opsonised HIV: A key to better vaccines?` supported by the Austrian Science Fund in 2009.