Nef Protein of Human Immunodeficiency Virus and Lipopolysaccharide Induce Expression of CD14 on Human Monocytes through Differential Utilization of Interleukin-10

Abstract

We investigated the expression of membrane-bound CD14 (mCD14) on monocytes and soluble CD14 (sCD14) released into the culture supernatants of peripheral blood lymphocytes (PBMC) from human immunodeficiency virus (HIV)-infected individuals. Monocytes from HIV-positive individuals exhibited both enhanced mCD14 expression and sCD14 production in the PBMC culture supernatants compared to the levels of mCD14 and sCD14 in HIV-negative individuals. This enhanced mCD14 expression and sCD14 production in HIV-infected individuals may be due to the effects of cytokines, the bacterial product lipopolysaccharide (LPS), and/or the HIV regulatory antigens Tat and Nef. Interleukin-10 (IL-10), an immunoregulatory cytokine, as well as LPS enhanced mCD14 expression and the release of sCD14 in the culture supernatants. HIV-Nef, unlike Tat, enhanced mCD14 expression on monocytes but did not induce the release of sCD14 into the culture supernatants. Studies conducted to investigate the mechanism underlying HIV-Nef-induced mCD14 expression revealed that HIV-Nef upregulated mCD14 expression via a mechanism that does not involve endogenously produced IL-10. In contrast, LPS upregulated the expression of mCD14 and increased the release of sCD14 via a mechanism that involves, at least in part, endogenously produced IL-10. Furthermore, dexamethasone, an anti-inflammatory and immunosuppressive agent, inhibited HIV-Nef-induced CD14 expression in an IL-10-independent manner. In contrast, dexamethasone inhibited IL-10-dependent LPS-induced CD14 expression by interfering with IL-10-induced signals but not by blocking IL-10 production. These results suggest that HIV-Nef and IL-10 constitute biologically important modulators of CD14 expression which may influence immunobiological responses to bacterial infections in HIV disease.

HIV-1 Nef Inhibits Lipopolysaccharide-induced IL-12p40 Expression by Inhibiting JNK-activated NFκB in Human Monocytic Cells

“…THP-1 cells infected with nef retroviruses produced 114 Ϯ 102 pg/ml IL-10 as compared with the 142 Ϯ 110 pg/ml in cells infected with control viruses following LPS stimulation. These results confirmed our prior observations that recombinant nef did not affect LPS-induced IL-10 production (38). Equal infectivity of primary monocytes and THP-1 cells with nef retroviruses was shown by performing RT-PCR analysis on the same samples for the neomycin gene present in both nef and pSR␣ retroviruses (Fig.…”

STAT-1 Mediates the Stimulatory Effect of IL-10 on CD14 Expression in Human Monocytic Cells

“…The interaction of LPS with CD14 on monocytic cells plays a critical role in the activation of these cells during inflammation and sepsis (31). CD14 is one of the few surface receptors whose expression is enhanced by IL-10 on human monocytes (30). In this study, we investigated the molecular mechanism by which IL-10 induces upregulation of surface CD14 by using primary human monocytes and promyelocytic HL-60 cells as model systems.…”

“…We have previously demonstrated that LPS, a component of Gram-negative bacterial cell walls, induced CD14 expression (30). CD14 is the primary LPS receptor expressed on cells of the monomyelocytic lineage (31).…”

“…CD14 expression on monocytes and HL-60 cells was determined by flow cytometry as previously described (30). Briefly, cells were stained with PE-conjugated anti-CD14 mAbs (BD Biosciences).…”

Monocytes and their Role in Human Immunodeficiency Virus Pathogenesis

“…A recent study undertaken by Creery et al (2002) showed that the HIV-regulatory protein Nef upregulated mCD14 expression but fails to induce the release of sCD14. Higher levels of mCD14 and circulating sCD14 in HIV-infected individuals may reflect their chronic state of inflammation and may be involved in enhanced susceptibility to gram-negative infections (Creery et al, 2002).…”