Evidence of inflammasome activation and formation of monocyte-derived ASC specks in HIV-1 positive patients

Abstract

Objective: The formation of large intracellular protein aggregates of the inflammasome adaptor protein ASC (apoptosis-associated speck-like protein containing a caspase-recruitment domain; also know as PYCARD) is a hallmark of inflammasome activation. ASC speck-forming cells release the highly proinflammatory cytokine IL-1β in addition to ASC specks into the extracellular space during pyroptotic cell death. There ASC specks can propagate inflammation to other nonactivated cells or tissues. HIV-1 retroviral infection triggers inflammasome activation of abortively infected CD4⁺ T cells in secondary lymphatic tissues. However, if pyroptosis occurs in other peripheral blood mononuclear cells (PBMCs) of HIV-1-infected patients is currently unknown. We investigated if ASC speck positive cells are present in the circulation of HIV-1-infected patients.

Design and methods: PBMCs or plasma of HIV-1 infected, antiretroviral therapy-naive patients were analyzed for the presence of ASC speck⁺ cells or extracellular ASC and compared with healthy controls. Intracellular staining for ASC was employed to detect ASC speck⁺ cells within PBMCs by flow cytometry, and ELISA to detect free ASC in the plasma. ASC multimerization was confirmed by immunoblot.

Results: Peripheral blood CD14⁺⁺CD16⁻ monocytes were ASC speck⁺ in HIV patients, but not in healthy controls. In the subgroup analysis, HIV patients with lower CD4⁺ T-cell counts and higher viral load had significantly more ASC speck⁺ monocytes. ASC speck formation did not correlate with Gag expression, coinfection, lactate dehydrogenase or C-reactive protein.

Conclusion: Our findings suggest that pyroptotic CD14⁺⁺CD16⁻ classical monocytes of HIV-1-infected patients release ASC specks into the blood stream, a phenomenon that may contribute to HIV-1 induced inflammation and immune activation.