1000/1000
Hot
Most Recent
| Version | Summary | Created by | Modification | Content Size | Created at | Operation |
|---|---|---|---|---|---|---|
| 1 | José Miguel Azevedo-Pereira | -- | 1761 | 2023-04-14 12:09:22 | | | |
| 2 | José Miguel Azevedo-Pereira | + 10 word(s) | 1766 | 2023-04-14 18:11:44 | | | | |
| 3 | José Miguel Azevedo-Pereira | Meta information modification | 1766 | 2023-04-14 18:13:41 | | | | |
| 4 | José Miguel Azevedo-Pereira | + 22 word(s) | 1788 | 2023-04-14 18:20:24 | | | | |
| 5 | Peter Tang | Meta information modification | 1788 | 2023-04-17 08:37:05 | | |
Human immunodeficiency virus (HIV) types 1 and 2 (HIV-1 and HIV-2, respectively) are the causative agents of acquired immunodeficiency syndrome (AIDS). At the end of 2021, an estimated 38.4 million people were infected with HIV (mainly HIV-1), which has claimed 40.1 million lives since the beginning of the AIDS pandemic. Even in the presence of highly active and multi-target antiretroviral drugs, HIV resists eradication. More importantly, through the direct induction of CD4+ lymphocyte depletion and the establishment of a chronic inflammatory environment, HIV infection is the primary driver of premature immune senescence and exhaustion, creating a series of deleterious conditions that enable the proliferation and decontrol of multiple pathogens, the development of tumors, and the onset of other non-AIDS comorbidities such as neurocognitive disorders and cardiovascular disease.
HIV is mainly transmitted through unprotected vaginal, anal, and oral sex. HIV can also be transmitted by blood transfusion, the sharing of contaminated needles, and vertical transmission from an infected and untreated mother to her child during pregnancy, childbirth, and breastfeeding. Following HIV transmission through the sexual mucosa, viral spread occurs through draining lymph nodes and the bloodstream, allowing viral infection to spread to multiple compartments of the body, namely the brain, lungs, and gut-associated lymphoid tissue (GALT) [1].
T-CD4+ lymphocytes and macrophages are the major target cells for HIV infection and replication in vivo. Although infection of the latter is characteristically non-cytopathic, allowing for the survival of infected macrophages with low levels of virus production throughout the cell’s life [8], infection of T-CD4+ lymphocytes invariably leads to their destruction and to an irreversible depletion of this crucial immune cell population [9]. This depletion is observed in the peripheral blood, as reflected by a decrease in circulating T-CD4+ lymphocytes [10], but it has also been documented in mucosa-associated lymphoid tissues, such as GALT [11][12].
One of the key questions in HIV pathogenesis concerns how CD4+ T lymphocytes die during HIV infection. One of the processes involved is the apoptosis of infected and bystander non-infected cells [13][14]. The death of non-infected bystander cells involves multiple mechanisms and players and includes the activation of host cell pathways (e.g., FAS ligand, TNF-α, TRAIL) that induce apoptotic events [13][15][16], and the effect of viral proteins released from infected cells that induce bystander cell death, such as Nef, Tat, Vpr, or Vpu [17][18][19][20][21].
One of the most important features of the HIV life cycle in an infected human host is resistance to eradication, even in the presence of highly active and multi-target antiretroviral drugs. In addition, when antiretroviral therapy (ART) is stopped, HIV viremia that was suppressed and undetectable during ART rebounds and returns to pre-ART levels.
This inability to cure HIV infection has been the subject of intense research and is based on HIV’s ability to infect cells that act as cellular reservoirs in multiple body compartments. These cells are latently infected, as defined by the absence of viral production, and consist mainly of memory CD4+ T lymphocytes, monocytes, and macrophages.
The establishment of latency is one of the strategies used by HIV to persist in infected hosts; it results from the HIV replication cycle, in which viral double-stranded DNA is retrotranscribed from genomic RNA. Under certain circumstances, this proviral DNA can be maintained in a non- transcriptional state so that HIV antigens are not expressed, and infected cells cannot be detected and targeted for a cytolytic lymphocyte response.
There are two types of latency: pre-integration latency and post-integration latency. Pre- integration latency is defined by the presence of complete or incomplete forms of viral double- stranded DNA that are not integrated into the cellular chromosomes. It appears to be quite common and occurs in resting CD4+ T lymphocytes [26][27][28][29]. However, the pre-integrated form of viral DNA in resting CD4+ T lymphocytes appears to be labile and short-lived, with a half- life of approximately one day [28], although other reports have found a longer lifespan of one week [30].
Post-integration latency in memory CD4+ T lymphocytes is considered the true latency state responsible for the lifelong persistence of HIV in an infected host. It is established after the integration step of the retroviral replication cycle and relies on the complete silencing of proviral transcription. The mechanisms underlying this non-transcriptional state include the epigenetic regulation of proviral transcription and post-transcriptional regulation (reviewed in [31]). Furthermore, it has been noted that the survival of latently infected CD4+ T lymphocytes in patients on long-term ART regimens depends not only on HIV gene silencing, but also on high expression levels of immune checkpoint molecules that negatively regulate T lymphocyte immune function [32][33][34][35][36].
In addition to CD4+ T lymphocytes, cells of the monocyte/macrophage lineage are also susceptible to HIV infection soon after transmission through genital and anorectal mucosa [37]. This susceptibility includes both those viruses that enter the cells through engagement of the CD4 and CCR5 chemokine receptors (R5 viruses) and those that use the CD4 and CXCR4 chemokine receptors (X4 viruses) [38][39][40]. This cell group includes peripheral blood monocytes, tissue macrophages, dendritic cells, and Langerhans cells.