**1. Introduction**

Combined antiretroviral therapy (cART) does not eradicate HIV-1 [1,2] due to the early establishment of a long-lived viral reservoir [3–6]. This reservoir can include cells of macrophage lineage

where, in contrast to CD4+ lymphocytes, HIV is relatively non cytopathic and can replicate extensively in intracellular compartments in a long-lasting manner [7–10]. HIV-1 infected monocyte-derived macrophages (MDM) are fully capable of producing infectious viral particles when cART is discontinued [11–16] and may play a key role in regulating the disease progression [17].

Over the following decades, after the discovery of CD4 as the main virus receptor [18,19], further studies have demonstrated that the chemokines coreceptors CCR5 and CXCR4 play crucial duties in supporting infection of HIV-1 in target cells.

Binding of chemokine receptors CCR5 or CXCR4 is widely thought to be the cause that stimulates the membrane fusion during HIV-replicative life cycle [19,20]. Infection with HIV-1 is generally initiated by macrophages, slowly replicating, non-syncytium-inducing (NSI) variants [20,21] that utilize CCR5 as a coreceptor [22–24]. In 50% of instances, disease evolution is correlated with the development of syncytium-inducing (SI) variants which at least use CXCR4 [25–28].

The tropism of HIV-1 for specific and relevant cell populations in diverse compartments is determined by the coreceptor utilized by HIV-1 Env for the entrance of the viral particles [28]. For infection of MDM cultures, HIV viruses preferentially utilize CCR5 as a coreceptor [22–26], whereas viruses in T-cells use CXCR4 [27]. Dual-tropic viruses can utilize both coreceptors (CCR5/CXCR4) [29,30]. Thus, the coreceptor particularity of primary HIV-1 isolates is commonly utilized to characterize cellular tropism [31].

Previous studies have shown that CCR5 is present on a wide variety of cells that can be infected by HIV-viruses, including T cells, monocytes and macrophages. A lot of research has shown the existence of CCR5-tropic viruses, which were proficient in replication of primary CD4+ T cells but which could not e ffectively infect MDM [32–38]. Also, some CCR5-tropic primary HIV-1 strains utilize CXCR4 for input into MDM [32,38]. Hence, the viral determinants that regulate HIV-1 tropism for macrophages are considerably more complicated than the coreceptor specificity of the virus. HIV-1 viruses use CCR5 for their infection, although their primary targets are T cells not macrophages. It is widely agreed that these CCR5 and CXCR4 viruses can replicate in both macrophages as well as in T cells. However, their replication e ffectiveness changes in di fferent cell classes which depend upon the cellular environment [37,38]. Moreover, viral progeny from macrophages and T cells may have divergent groups of host protein integrated in their viral particle [39].

HIV-mediated patterns of replication in latently infected cells (virus reservoir) have not been completely understood. HIV infections lead to increased expression of specific proteins like B-cell lymphoma 2 (BCL-2), B-cell lymphoma-extra large (BCL-XL), cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein (cFLIP), Induced myeloid leukemia cell di fferentiation protein (Mcl-1) [40–42] or downregulation of proteins Bcl-2-associated X protein (BAX), Bcl-2-associated death promoter protein (BAD proteins), Fas-associated protein with death domain (FADD) [42–44]. These factors contribute to regulate the transcription of genes correlated with host defense, cellular anti-oxidant molecules like glutathione and thioredoxin, signal transduction, survival, and the cell cycle, including the cyclin-dependent kinase inhibitor 1A (CDKN1A/p21) gene whose maximum extent of mRNA and protein expression parallels active HIV-1 replication in latent cells.

This work aims at defining: (i) the role of CCR5-tropic and CXCR4- tropic strains in MDM; (ii) assessment of di fferent patterns of replication in this cell type by evaluating the extent of DNA degradation, viral production, p38 MAPK activation and survival gene modulation in CXCR4 and the CCR5 infected MDM.

#### **2. Materials and Methods**
