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BackgroundMacrophages are key targets of HIV-1 infection. We have previously described that the expression of CC chemokine ligand 2 (CCL2) increases during monocyte differentiation to macrophages and it is further up-modulated by HIV-1 exposure. Moreover, CCL2 acts as an autocrine factor that promotes viral replication in infected macrophages. In this study, we dissected the molecular mechanisms by which CCL2 neutralization inhibits HIV-1 replication in monocyte-derived macrophages (MDM), and the potential involvement of the innate restriction factors protein sterile alpha motif (SAM) histidine/aspartic acid (HD) domain containing 1 (SAMHD1) and apolipoprotein B mRNA-editing, enzyme-catalytic, polypeptide-like 3 (APOBEC3) family members.ResultsCCL2 neutralization potently reduced the number of p24 Gag+ cells during the course of either productive or single cycle infection with HIV-1. In contrast, CCL2 blocking did not modify entry of HIV-1 based Virus Like Particles, thus demonstrating that the restriction involves post-entry steps of the viral life cycle. Notably, the accumulation of viral DNA, both total, integrated and 2-LTR circles, was strongly impaired by neutralization of CCL2. Looking for correlates of HIV-1 DNA accumulation inhibition, we found that the antiviral effect of CCL2 neutralization was independent of the modulation of SAMHD1 expression or function. Conversely, a strong and selective induction of APOBEC3A expression, to levels comparable to those of freshly isolated monocytes, was associated with the inhibition of HIV-1 replication mediated by CCL2 blocking. Interestingly, the CCL2 neutralization mediated increase of APOBEC3A expression was type I IFN independent. Moreover, the transcriptome analysis of the effect of CCL2 blocking on global gene expression revealed that the neutralization of this chemokine resulted in the upmodulation of additional genes involved in the defence response to viruses.ConclusionsNeutralization of endogenous CCL2 determines a profound restriction of HIV-1 replication in primary MDM affecting post-entry steps of the viral life cycle with a mechanism independent of SAMHD1. In addition, CCL2 blocking is associated with induction of APOBEC3A expression, thus unravelling a novel mechanism which might contribute to regulate the expression of innate intracellular viral antagonists in vivo. Thus, our study may potentially lead to the development of new therapeutic strategies for enhancing innate cellular defences against HIV-1 and protecting macrophages from infection.

Abstract: The apolipoprotein B mRNA editing enzyme catalytic polypeptide‐like 3 (APOBEC3) family of cytosine deaminases plays crucial roles in innate immunity through the ability of restricting viral replication by deamination and mutation of viral genomes. The antiviral function of these proteins was first discovered when research in the field of HIV infection revealed that one member of the family, namely APOBEC3G, restricts HIV infection in T lymphocytes and that the viral infectivity factor protein drives the proteosomal degradation of this enzyme, thus overriding its antiviral function. Recent advances in cancer genomics, together with biochemical characterization of the APOBEC3 enzymes, have now implicated some family members in somatic mutagenesis during carcinogenesis. While several studies investigated the downstream consequences of APOBEC3 expression and activity, either in the context of viral infection or tumorigenesis, little is known on the upstream mechanisms regulating APOBEC3 expression. Such knowledge would be of huge importance in developing innovative approaches to strengthen antiviral innate immunity on one side and to prevent cancer development on the other. This mini review summarizes research advances on the molecular mechanisms regulating the expression of APOBEC3 family members in selected immune cell populations and cancer cells. [ABSTRACT FROM AUTHOR]

Lactoferrin (LF) exhibits a wide range of immunomodulatory activities including modulation of cytokine and chemokine secretion. In this study, we demonstrate that bovine LF (bLF) up-modulates, in a concentration- and time-dependent manner, CCL1 secretion in monocytes (Mo) at the early stage of differentiation toward dendritic cells (DCs), and in fully differentiated immature Mo-derived DCs (MoDCs). In both cell types, up-modulation of CCL1 secretion is an early event following bLF-mediated enhanced accumulation of CCL1 transcripts. Notably, bLF-mediated up-regulation of CCL1 involves the engagement of distinct surface receptors in MoDCs and their Mo precursors. We show that bLF-mediated engagement of CD36 contributes to CCL1 induction in differentiating Mo. Conversely, toll-like receptor (TLR)2 blocking markedly reduces bLF-induced CCL1 production in MoDCs. These findings add further evidence for cell-specific differential responses elicited by bLF through the engagement of distinct TLRs and surface receptors. Furthermore, the different responses observed at early and late stages of Mo differentiation towards DCs may be relevant in mediating bLF effects in specific body districts, where these cell types may be differently represented in physiopathological conditions. [ABSTRACT FROM AUTHOR]

The identification of chemokine receptors as necessary co-receptors for HIV entry into target cells represented a breakthrough in the understanding of the pathogenesis of this viral infection. Since this initial discovery, it was unraveled that chemokines, in addition to their role in blocking viral entry by binding to co-receptors, have other functions in HIV pathogenesis. Indeed, chemokines can either inhibit or enhance HIV replication, and these effects may involve both entry and post-entry events of the viral life cycle. Depending on the balance of their negative versus positive effects on HIV replication and spreading, chemokines contribute to different outcomes of HIV pathogenesis. CCL2 is unique among the chemokines in that mostly enhancing effects on viral replication and pathogenesis have been reported. Either HIV infection itself or exposure to viral products can induce the expression of this chemokine and of its receptor CCR2, and high levels of CCL2/CCR2 are indeed found in HIV-infected subjects. The CCL2/CCR2 axis is tightly linked to the high level of immune activation and inflammation that is the hallmark of HIV infection even in patients undergoing antiretroviral therapy. In addition, more direct effects of CCL2 on HIV replication are becoming apparent. Thus, modulation of CCL2/CCR2-driven effects may have significant impact on HIV disease progression. In this review, we will discuss the complex interaction between CCL2/CCR2 and HIV and the emerging therapeutic approaches based on the inhibition of this axis.