Inhibitory and Stimulatory Effects of IL-32 on HIV-1 Infection

Abstract

The proinflammatory cytokine IL-32 is elevated in the plasma and tissues of HIV-1–infected individuals. However, its significance in HIV-1 infection remains unclear because IL-32 inhibits and stimulates viral production in monocyte-derived macrophages (MDMs) and CD4+ T cells, respectively. In this study, we initially found that the inhibitory effect on human MDMs depends on SAMHD1, a dNTP triphosphohydrolase that inhibits viral reverse transcription. IL-32 increased the unphosphorylated active form of SAMHD1, which was consistent with the reduced expression of the upstream cyclin-dependent kinases. Indeed, IL-32 lost its anti–HIV-1 activity in MDMs when SAMHD1 was depleted. These results explain why IL-32 inhibits HIV-1 in MDMs but not CD4+ T cells, because SAMHD1 restricts HIV-1 in noncycling MDMs but not in cycling CD4+ T cells. Another unique feature of IL-32 is the induction of the immunosuppressive molecule IDO1, which is beneficial for HIV-1 infection. In this study, we found that IL-32 also upregulates other immunosuppressive molecules, including PD-L1, in MDMs. Moreover, IL-32 promoted the motility of MDMs, which potentially facilitates intercellular HIV-1 transmission. Our findings indicate that IL-32 has both the direct inhibitory effect on HIV-1 production in MDMs and the indirect stimulatory effects through phenotypic modulation of MDMs, and they suggest that the stimulatory effects may outweigh the inhibitory effect because the window for IL-32 to inhibit HIV-1 is relatively confined to SAMHD1-mediated reverse transcription suppression in the viral life cycle.

CD34-positive monocytes are highly susceptible to HIV-1

“…CD34 + monocytes (CD3 − CD14 + CD16 − CD34 + ) or CD34 − monocytes (CD3 − CD14 + CD16 − CD34 − ) of healthy donors were purified by sorting, and cellular RNA was isolated using RNeasy micro kit (QIAGEN). Complementary DNA was prepared using M-MLV RT (Invitrogen), and quantitative PCR (qPCR) was performed with SYBR Premix Ex Taq II (TaKaRa-Bio) using a LightCycler (Roche) as described previously (18). The expression levels of mRNA of HIV-1 restriction factors (MX2, SAMHD1, BST2, and APOBEC3G) were calculated using the ΔΔCt method and normalized to that of GAPDH.…”

“…was isolated using RNeasy micro kit (QIAGEN). Complementary DNA was prepared using M-MLV RT (Invitrogen), and quantitative PCR (qPCR) was performed with SYBR Premix Ex Taq II (TaKaRa-Bio) using a LightCycler (Roche) as described previously (18).…”