Dionna W. Williams

Monocytes mediate HIV neuropathogenesis: mechanisms that contribute to HIV associated neurocognitive disorders.

HIV infected people are living longer due to the success of combined antiretroviral therapy (cART). However, greater than 40-70% of HIV infected individuals develop HIV associated neurocognitive disorders (HAND) that continues to be a major public health issue. While cART reduces peripheral virus, it does not limit the low level, chronic neuroinflammation that is ongoing during the neuropathogenesis of HIV. Monocyte transmigration across the blood brain barrier (BBB), specifically that of the mature CD14(+)CD16(+) population that is highly susceptible to HIV infection, is critical to the establishment of HAND as these cells bring virus into the brain and mediate the neuroinflammation that persists, even if at low levels, despite antiretroviral therapy. CD14(+)CD16(+) monocytes preferentially migrate into the CNS early during peripheral HIV infection in response to chemotactic signals, including those from CCL2 and CXCL12. Once within the brain, monocytes differentiate into macrophages and elaborate inflammatory mediators. Monocytes/macrophages constitute a viral reservoir within the CNS and these latently infected cells may perpetuate the neuropathogenesis of HIV. This review will discuss mechanisms that mediate transmigration of CD14(+)CD16(+) monocytes across the BBB in the context of HIV infection, the contribution of these cells to the neuropathogenesis of HIV, and potential monocyte/macrophage biomarkers to identify HAND and monitor its progression.

Astrocyte-shed extracellular vesicles regulate the peripheral leukocyte response to inflammatory brain lesions

Vesicles shed from astrocytes after brain trauma trigger hepatic cytokine release to mobilize the peripheral immune response. An astrocyte “call to arms” after brain injury Brain injuries, such as stroke, physical trauma, and inflammation, stimulate the infiltration of peripheral immune cells that may cause persistent, secondary tissue damage that can impair patient recovery. Using a mouse model of inflammatory brain injury, Dickens et al. found that astrocytes at the site of inflammation released vesicles carrying proteins, RNAs, and microRNAs into the circulation. When these vesicles reached the liver, they stimulated the secretion of cytokines that mobilized peripheral immune cells to infiltrate the brain. Inhibiting this long-range communication between the brain and the liver might accelerate and improve recovery from brain injuries. Brain injury induces a peripheral acute cytokine response that directs the transmigration of leukocytes into the brain. Because this brain-to-peripheral immune communication affects patient recovery, understanding its regulation is important. Using a mouse model of inflammatory brain injury, we set out to find a soluble mediator for this phenomenon. We found that extracellular vesicles (EVs) shed from astrocytes in response to intracerebral injection of interleukin-1β (IL-1β) rapidly entered into peripheral circulation and promoted the transmigration of leukocytes through modulation of the peripheral acute cytokine response. Bioinformatic analysis of the protein and microRNA cargo of EVs identified peroxisome proliferator–activated receptor α (PPARα) as a primary molecular target of astrocyte-shed EVs. We confirmed in mice that astrocytic EVs promoted the transmigration of leukocytes into the brain by inhibiting PPARα, resulting in the increase of nuclear factor κB (NF-κB) activity that triggered the production of cytokines in liver. These findings expand our understanding of the mechanisms regulating communication between the brain and peripheral immune system and identify astrocytic EVs as a molecular regulator of the immunological response to inflammatory brain damage.

CCR2 on CD14+CD16+ monocytes is a biomarker of HIV-associated neurocognitive disorders

Objective: To evaluate C-C chemokine receptor type 2 (CCR2) on monocyte subsets as a prognostic peripheral blood biomarker of HIV-associated neurocognitive disorders (HAND). Methods: We characterized monocyte populations in HIV-infected individuals with and without HAND from 2 cohorts and assessed their transmigration across an in vitro model of the human blood-brain barrier (BBB). We examined CCR2 expression among the monocyte populations as a prognostic/predictive biomarker of HAND and its functional consequences in facilitating monocyte diapedesis. Results: We determined that CCR2 was significantly increased on CD14+CD16+ monocytes in individuals with HAND compared to infected people with normal cognition. CCR2 remained elevated irrespective of the severity of cognitive impairment, combined antiretroviral therapy status, viral load, and current or nadir CD4 T-cell count. There was no association between CCR2 on other monocyte populations and HAND. There was a functional consequence to the increase in CCR2, as CD14+CD16+ monocytes from individuals with HAND transmigrated across our model of the human BBB in significantly higher numbers in response to its ligand chemokine (C-C) motif ligand 2 (CCL2) compared to the cell migration that occurred in people with no cognitive deficits. It should be noted that our study had the limitation of a smaller sample size of unimpaired individuals. In contrast, there was no difference in the transmigration of other monocyte subsets across the BBB in response to CCL2 in seropositive individuals with or without HAND. Conclusions: Our findings indicate CCR2 on CD14+CD16+ monocytes is a novel peripheral blood biomarker of HAND.

JAM-A and ALCAM are therapeutic targets to inhibit diapedesis across the BBB of CD14+CD16+ monocytes in HIV-infected individuals

Monocyte transmigration across the BBB is a critical step in the development of cognitive deficits termed HAND that affect 40–70% of HIV‐infected individuals, even with successful antiretroviral therapy. The monocyte subsets that enter the CNS during HIV infection are not fully characterized. We examined PBMC from HIV‐positive individuals from 2 distinct cohorts and enumerated monocyte populations, characterized their transmigration properties across an in vitro human BBB model, and identified surface proteins critical for the entry of these cells into the CNS. We demonstrated that the frequency of peripheral blood CD14+CD16+ and CD14lowCD16+ monocytes was increased in HIV‐seropositive compared with ‐seronegative individuals, despite virologic control. We showed that CD14+CD16+ monocytes selectively transmigrated across our BBB model as a result of their increased JAM‐A and ALCAM expression. Antibody blocking of these proteins inhibited diapedesis of CD14+CD16+ monocytes but not of T cells from the same HIV‐infected people across the BBB. Our data indicate that JAM‐A and ALCAM are therapeutic targets to decrease the entry of CD14+CD16+ monocytes into the CNS of HIV‐seropositive individuals, contributing to the eradication of neuroinflammation, HAND, and CNS viral reservoirs.

Splenic Damage during SIV Infection : Role of T-Cell Depletion and Macrophage Polarization and Infection

The effects of HIV infection on spleen and its cellular subsets have not been fully characterized, particularly for macrophages in which diverse populations exist. We used an accelerated SIV-infected macaque model to examine longitudinal effects on T-cell and macrophage populations and their susceptibilities to infection. Substantial lymphoid depletion occurred, characterized by follicular burn out and a loss of CD3 T lymphocytes, which was associated with cellular activation and transient dysregulations in CD4/CD8 ratios and memory effector populations. In contrast, the loss of CD68 and CD163(+)CD68(+) macrophages and increase in CD163 cells was irreversible, which began during acute infection and persisted until terminal disease. Mac387 macrophages and monocytes were transiently recruited into spleen, but were not sufficient to mitigate the changes in macrophage subsets. Type I interferon, M2 polarizing genes, and chemokine-chemokine receptor signaling were up-regulated in spleen and drove macrophage alterations. SIV-infected T cells were numerous within the white pulp during acute infection, but were rarely observed thereafter. CD68, CD163, and Mac387 macrophages were highly infected, which primarily occurred in the red pulp independent of T cells. Few macrophages underwent apoptosis, indicating that they are a long-lasting target for HIV/SIV. Our results identify macrophages as an important contributor to HIV/SIV infection in spleen and in promoting morphologic changes through the loss of specific macrophage subsets that mediate splenic organization.

Dopamine Increases CD14(+)CD16(+) Monocyte Transmigration across the Blood Brain Barrier: Implications for Substance Abuse and HIV Neuropathogenesis.

In human immunodeficiency virus-1 (HIV) infected individuals, substance abuse may accelerate the development and/or increase the severity of HIV associated neurocognitive disorders (HAND). It is proposed that CD14+CD16+ monocytes mediate HIV entry into the central nervous system (CNS) and that uninfected and infected CD14+CD16+ monocyte transmigration across the blood brain barrier (BBB) contributes to the establishment and propagation of CNS HIV viral reservoirs and chronic neuroinflammation, important factors in the development of HAND. The effects of substance abuse on the frequency of CD14+CD16+ monocytes in the peripheral circulation and on the entry of these cells into the CNS during HIV neuropathogenesis are not known. PBMC from HIV infected individuals were analyzed by flow cytometry and we demonstrate that the frequency of peripheral blood CD14+CD16+ monocytes in HIV infected substance abusers is increased when compared to those without active substance use. Since drug use elevates extracellular dopamine concentrations in the CNS, we examined the effects of dopamine on CD14+CD16+ monocyte transmigration across our in vitro model of the human BBB. The transmigration of this monocyte subpopulation is increased by dopamine and the dopamine receptor agonist, SKF 38393, implicating D1-like dopamine receptors in the increase in transmigration elicited by this neurotransmitter. Thus, elevated extracellular CNS dopamine may be a novel common mechanism by which active substance use increases uninfected and HIV infected CD14+CD16+ monocyte transmigration across the BBB. The influx of these cells into the CNS may increase viral seeding and neuroinflammation, contributing to the development of HIV associated neurocognitive impairments.

Frontline Science: CXCR7 mediates CD14+CD16+ monocyte transmigration across the blood brain barrier: a potential therapeutic target for NeuroAIDS

CD14+CD16+ monocytes transmigrate into the CNS of HIV‐positive people in response to chemokines elevated in the brains of infected individuals, including CXCL12. Entry of these cells leads to viral reservoirs, neuroinflammation, and neuronal damage. These may eventually lead to HIV‐associated neurocognitive disorders. Although antiretroviral therapy (ART) has significantly improved the lives of HIV‐infected people, the prevalence of cognitive deficits remains unchanged despite ART, still affecting >50% of infected individuals. There are no therapies to reduce these deficits or to prevent CNS entry of CD14+CD16+ monocytes. The goal of this study was to determine whether CXCR7, a receptor for CXCL12, is expressed on CD14+CD16+ monocytes and whether a small molecule CXCR7 antagonist (CCX771) can prevent CD14+CD16+ monocyte transmigration into the CNS. We showed for the first time that CXCR7 is on CD14+CD16+ monocytes and that it may be a therapeutic target to reduce their entry into the brain. We demonstrated that CD14+CD16+ monocytes and not the more abundant CD14+CD16− monocytes or T cells transmigrate to low homeostatic levels of CXCL12. This may be a result of increased CXCR7 on CD14+CD16+ monocytes. We showed that CCX771 reduced transmigration of CD14+CD16+ monocytes but not of CD14+CD16− monocytes from uninfected and HIV‐infected individuals and that it reduced CXCL12‐mediated chemotaxis of CD14+CD16+ monocytes. We propose that CXCR7 is a therapeutic target on CD14+CD16+ monocytes to limit their CNS entry, thereby reducing neuroinflammation, neuronal damage, and HIV‐associated neurocognitive disorders. Our data also suggest that CCX771 may reduce CD14+CD16+ monocyte‐mediated inflammation in other disorders.

A fully human antibody to gp41 selectively eliminates HIV-infected cells that transmigrated across a model human blood brain barrier

Objective:Many HIV patients on combined antiretroviral therapy exhibit HIV-associated neurocognitive disorders because the brain becomes a viral reservoir. There is a need for therapeutics that can enter the central nervous system (CNS) and eradicate the virus. Design:Radiolabeled human mAb 2556 to HIV gp41 selectively kills HIV-infected cells in vivo and in vitro. Here we tested the ability of 213Bi-2556 to cross a tissue culture model of the human blood brain barrier and kill HIV-infected peripheral blood mononuclear cells (PBMCs) and monocytes on the CNS side of the barrier. Methods:2556 mAb isoelectric point was determined with isoelectric focusing. The ability of radiolabeled 2556 to penetrate through the barrier was studied by adding it to the upper chamber of the barriers and its penetration into the CNS side was followed for 5 h. To assess the ability of 213Bi-2556 to kill the HIV-infected cells on the CNS side of barrier, the HIV-infected and uninfected PBMCs and monocytes were allowed to transmigrate across the barriers overnight followed by application of 213Bi-2556 or control mAb 213Bi-1418 to the top of the barrier. Killing of cells was measured by TUNEL and Trypan blue assays. The barriers were examined by confocal microscopy for overt damage. Results:The isoelectric point of 213Bi-2556 was 9.6 enabling its penetration through the barrier by transcytosis. 213Bi-2556 killed significantly more transmigrated HIV-infected cells in comparison to 213Bi-1418 and uninfected cells. No overt damage to barriers was observed. Conclusion:We demonstrated that 213Bi-2556 mAb crossed an in-vitro human blood brain barrier and specifically killed transmigrated HIV-infected PBMCs and monocytes without overt damage to the barrier.

CCR2 on Peripheral Blood CD14+CD16+ Monocytes Correlates with Neuronal Damage, HIV-Associated Neurocognitive Disorders, and Peripheral HIV DNA: reseeding of CNS reservoirs?

HIV-associated neurocognitive disorders (HAND) occur in ~50% of HIV infected individuals despite combined antiretroviral therapy. Transmigration into the CNS of CD14+CD16+ monocytes, particularly those that are HIV infected and express increased surface chemokine receptor CCR2, contributes to neuroinflammation and HAND. To examine whether in HIV infected individuals CCR2 on CD14+CD16+ monocytes serves as a potential peripheral blood biomarker of HAND, we examined a cohort of 45 HIV infected people. We correlated CCR2 on CD14+CD16+ monocytes with cognitive status, proton magnetic resonance spectroscopy (1H-MRS) measured neurometabolite levels, and peripheral blood mononuclear cell (PBMC) HIV DNA copies. We determined that CCR2 was increased specifically on CD14+CD16+ monocytes from people with HAND (median [interquartile range (IQR)]) (63.3 [51.6, 79.0]), compared to those who were not cognitively impaired (38.8 [26.7, 56.4]) or those with neuropsychological impairment due to causes other than HIV (39.8 [30.2, 46.5]). CCR2 was associated with neuronal damage, based on the inverse correlation of CCR2 on CD14+CD16+ monocytes with total N-Acetyl Aspartate (tNAA)/total Creatine (tCr) (r2 = 0.348, p = 0.01) and Glutamine-Glutamate (Glx)/tCr (r2 = 0.356, p = 0.01) in the right and left caudate nucleus, respectively. CCR2 on CD14+CD16+ monocytes also correlated with PBMC HIV DNA copies (ρ = 0.618, p = 0.02) that has previously been associated with HAND. These findings suggest that CCR2 on CD14+CD16+ monocytes may be a peripheral blood biomarker of HAND, indicative of increased HIV infected CD14+CD16+ monocyte entry into the CNS that possibly increases the macrophage viral reservoir and contributes to HAND.