Upregulation of IL-32 Isoforms in Virologically Suppressed HIV-Infected Individuals: Potential Role in Persistent Inflammation and Transcription From Stable HIV-1 Reservoirs

BACKGROUND: Human IL-32 is a polyfunctional cytokine that was initially reported to inhibit HIV-1 infection. However, recent data suggest that IL-32 may enhance HIV-1 replication by activating the HIV-1 primary targets, CD4 T-cells. Indeed, IL-32 is expressed in multiple isoforms, some of which are proinflammatory, whereas others are anti-inflammatory. SETTING AND METHODS: Here, we aimed to determine the relative expression of IL-32 isoforms and to test their inflammatory nature and potential to induce HIV-1 production in latently infected cells from virologically suppressed HIV-infected individuals. IL-32 and other cytokines were quantified from plasma and supernatant of CD4 T-cells by ELISA. Transcripts of IL-32 isoforms were quantified by qRT-PCR in peripheral blood mononuclear cells. The impact of recombinant human IL-32 isoforms on HIV-1 transcription was assessed in CD4 T-cells from HIV-1cART individuals by qRT-PCR. RESULTS: All IL-32 isoforms were significantly upregulated in HIV-1cART compared to HIV individuals with IL-32beta representing the dominantly expressed isoform, mainly in T-cells and NK-cells. At the functional level, although IL-32gamma induced typical proinflammatory cytokines (IL-6 and IFN-gamma) in TCR-activated CD4 T-cells, IL-32alpha showed an anti-inflammatory profile by inducing IL-10 but not IL-6 or IFN-gamma. However, IL-32beta showed a dual phenotype by inducing both pro- and anti-inflammatory cytokines. Interestingly, consistent with its highly pro-inflammatory nature, IL-32gamma, but not IL-32alpha or IL-32beta, induced HIV-1 production in latently infected CD4 T-cells isolated from combined antiretroviral therapy-treated individuals. CONCLUSIONS: Our data report on the differential expression of IL-32 isoforms and highlight the potential role of IL-32, particularly the gamma isoform, in fueling persistent inflammation and transcription of viral reservoir in HIV-1 infection.