Background
Inflammasome activation in response to “danger-associated stimuli” including HIV can lead to the release of inflammatory cytokines such as IL-1ß and IL-18 as well as pyroptotic cell death. The HIV-1 protease can activate the CARD8 inflammasome in CD4 T cells, resulting in T-cell loss during untreated HIV infection. Since myeloid cells are equipped to mount an inflammatory response upon inflammasome activation, we hypothesize that CARD8 activation in these cells might be driving IL-18 production upon HIV infection.
Methods
We tested our hypothesis using an in vitro, ex vivo, and in vivo model. In vitro, we cocultured monocyte-derived macrophages (MDMs) with HIV-infected autologous CD4 T cells (CD4s) or HIV viral particles. We used either CARD8 knockout (KO) or Cas9 control cells. Ex vivo, we co-cultured MDMs with autologous CD4s from people living with HIV (PLWH) in which latent HIV-1 was reactivated by CD3/CD28 antibodies. For in vivo experiments, humanized mice were engrafted with either Cas9 control or CARD8 KO CD34+ cells, and then infected with HIV at week 9. Plasma or supernatant levels of IL-18 were measured by ELISA. P values were calculated using t test or ANOVA test.
Results
Coculture of MDMs with autologous CD4s infected with CCR5-tropic HIV or from PLWH resulted in higher levels of IL-18 compared to controls. Cytokine release was not triggered by free viral particles or X4-infected CD4s. Coculture with CARD8 KO CD4s resulted in significantly lower levels of IL-18 compared to Cas9 only controls. In humanized mice, CARD8 KO did not affect overall human CD45 engraftment, CD4 development or HIV viral loads. CARD8 KO and Cas9 control mice had similar IL-18 at baseline. However, CARD8 KO mice had a blunted inflammatory response to HIV compared to controls. While IL-18 levels trended up after infection in both groups, this increase was significant only in the Cas9 control group.
Conclusions
CARD8 inflammasome activation drives the release of inflammatory cytokines from autologous myeloid cells in vitro and ex vivo. Moreover, CARD8 KO decreases IL-18 surge during untreated HIV infection in humanized mice. These findings offer novel insights into HIV pathogenesis since they provide a mechanism for myeloid cell activation during acute infection. Since inflammation appears to persist even during effective antiretroviral therapy, understanding the contribution of CARD8 activation in PLWH could offer new strategies to decrease chronic inflammation.
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