Clare L. V. Westhorpe

Background: In some studies HIV infection confers approximately two-fold higher risk of cardiac events compared with the general population. C-reactive protein (CRP) is a well-characterised biomarker of cardiac events in the general population and is also elevated in patients with HIV infection. The aim of this study was to determine the predictive value of CRP for cardiac events in HIV-infected individuals. Methods: We retrospectively analysed CRP levels in stored plasma samples from HIV-infected patients who did or did not experience a coronary event in a case-controlled manner. All CRP measurements were performed using a high-sensitivity assay (hs-CRP). Results: Of the study participants with samples available, we found slightly elevated hs-CRP levels in the cardiac cases (median 3.5, IQR 1.6–14.4, n = 23) compared with controls (median 2.6, IQR1.2–8.3, n = 49) which were shown to not be statistically significant P = 0.20. Analysis of CRP as a binary variable (=5 mg L–1) was also not statistically significant (OR: 1.32, 95% CI 0.48–3.63). Conclusions: CRP levels may indicate elevated risk of future cardiac events, however this must be interpreted with caution due to the generalised elevation of CRP during HIV infection. CRP has no predictive value for atherosclerosis, and further research is required to improve early prediction of cardiovascular disease in HIV infection.

Regulatory T cells (Tregs) play critical roles in restricting T cell–mediated inflammation. In the skin, this is dependent on expression of selectin ligands required for leukocyte rolling in dermal microvessels. However, whether there are differences in the molecules used by Tregs and proinflammatory T cells to undergo rolling in the skin remains unclear. In this study, we used spinning disk confocal microscopy in Foxp3-GFP mice to visualize rolling of endogenous Tregs in dermal postcapillary venules. Tregs underwent consistent but low-frequency rolling interactions under resting and inflamed conditions. At the early stage of the response, Treg adhesion was minimal. However, at the peak of inflammation, Tregs made up 40% of the adherent CD4+ T cell population. In a multiple challenge model of contact hypersensitivity, rolling of Tregs and conventional CD4+ T cells was mostly dependent on overlapping contributions of P- and E-selectin. However, after a second challenge, rolling of Tregs but not conventional CD4+ T cells became P-selectin independent, and Tregs showed reduced capacity to bind P-selectin. Moreover, inhibition of E-selectin at this time point resulted in exacerbation of inflammation. These findings demonstrate that in this multiple challenge model of inflammation, Treg selectin binding capacity and the molecular basis of Treg rolling can be regulated dynamically.

Chronic HIV infection is associated with increased risk of cardiovascular disease (CVD), including in patients with virological suppression. Persistent innate immune activation may contribute to the development of CVD via activation of monocytes in these patients. We investigated whether changes in monocyte phenotype predict subclinical atherosclerosis in virologically suppressed HIV-positive individuals with low cardiovascular risk. We enroled 51 virologically suppressed HIV-positive individuals not receiving protease inhibitors or statins and 49 age-matched uninfected controls in this study. Carotid artery intima-media thickness (cIMT) was used as a surrogate marker for CVD, and traditional risk factors, including Framingham risk scores, were recorded. Markers of monocyte activation (CD14, CD16, CCR2, CX3CR1, CD38, HLA-DR and CD11b) were measured in whole-blood samples by flow cytometry. Associations were assessed using univariate and multivariate median regressions. Median cIMT was similar between HIV-positive and HIV-negative participants (P = 0.3), although HIV-positive patients had significantly higher Framingham risk score (P = 0.009) and systemic inflammation. Expression of two monocyte markers, CD11b and CX3CR1, independently predicted carotid artery thickness in HIV-positive individuals after controlling for Framingham risk score (P = 0.025 and 0.015, respectively). These markers were not predictive of carotid artery thickening in controls. Our study indicates that monocyte surface markers may serve as novel predictors of CVD in HIV-positive individuals and is consistent with an important role for monocyte activation in the progression of HIV-related cardiovascular pathology.

Intravital microscopy has been essential in establishing the multi‐step paradigm that describes how leukocytes in the bloodstream interact with the blood vessel wall during the process of leukocyte recruitment. Much of this work has been performed in readily‐visualized tissues such as the mesentery and the cremaster muscle, where leukocyte‐endothelial cell interactions are restricted to postcapillary venules. However, the microvasculatures of the liver, lung and renal glomerulus differ markedly from these conventionally structured microvascular beds. Moreover, the liver, lung and kidney can be the target of life‐threatening leukocyte‐mediated inflammation. Therefore, a clear understanding of the mechanisms of leukocyte recruitment to these sites is critical. In this review, we examine the advances made in the understanding of leukocyte recruitment in the liver, lung and glomerulus, as determined using intravital microscopy. We describe how leukocyte recruitment to these sites occurs via mechanisms distinct from the conventional rolling/adhesion/transmigration paradigm, and in some cases involves adhesion molecules with minimal roles in conventional postcapillary venules. In addition, we describe how advanced forms of in vivo imaging in combination with novel approaches for labeling immune cell subsets is revealing new complexities in leukocyte function and immune cell interactions in these specialized microvascular beds.

In contrast with many capillary beds, the glomerulus readily supports leukocyte recruitment. However, little is known regarding the actions of leukocytes following their recruitment to glomeruli. We used multiphoton confocal microscopy to examine leukocyte behavior in the glomerular microvasculature. In normal glomeruli, neutrophils and monocytes were retained in capillaries for several minutes, remaining static or migrating intravascularly. Induction of glomerular inflammation resulted in an increase in the duration of retention of static and migratory leukocytes. In response to immune complex deposition, both static and migratory neutrophils generated oxidants in inflamed glomeruli via a Mac-1-dependent mechanism. Our results describe a new paradigm for glomerular inflammation, suggesting that the major effect of acute inflammation is to increase the duration of leukocyte retention in the glomerulus. Moreover, these findings describe a previously unknown form of multicellular intravascular patrolling that involves both monocytes and neutrophils, which may underlie the susceptibility of the glomerulus to inflammation.

CD163, a haptoglobin-hemoglobin (Hp-Hb) scavenger receptor, expressed by monocytes and macrophages, is important in resolution of inflammation. Age-related non-AIDS co-morbidities in HIV-infected individuals, particularly dementia and cardiovascular disease, result in part from effects of HIV-1 infection on monocyte and macrophage biology. CD163 co-expression on CD14+CD16++ monocytes has been proposed as a useful biomarker for HIV-1 disease progression and the presence of HIV associated dementia. Here we investigated CD163 expression on monocyte subsets ex vivo, on cultured macrophages, and soluble in plasma, in the setting of HIV-1 infection. Whole blood immunophenotyping revealed CD163 expression on CD14++CD16- monocytes but not on CD14+CD16++ monocytes (P = 0.004), supported by CD163 mRNA levels. Incubation with M-CSF induced CD163 protein expression on CD14+CD16++ monocytes to the same extent as CD14++CD16− monocytes. CD163 expression on CD14++CD16+ monocytes from HIV-infected subjects was significantly higher than from uninfected individuals, with a trend towards increased expression on CD14++CD16− monocytes (P = 0.019 and 0.069 respectively), which is accounted for by HIV-1 therapy including protease inhibitors. Shedding of CD163 was shown to predominantly occur from the CD14++CD16− subset after Ficoll isolation and LPS stimulation. Soluble CD163 concentration in plasma from HIV-1 infected donors was similar to HIV-1 uninfected donors. Monocyte CD163 expression in HIV-1 infected patients showed a complicated relationship with classical measures of disease progression. Our findings clarify technical issues regarding CD163 expression on monocyte subsets and further elucidates its role in HIV-associated inflammation by demonstrating that CD163 is readily lost from CD14++CD16− monocytes and induced in pro-inflammatory CD14+CD16++ monocytes by M-CSF. Our data show that all monocyte subsets are potentially capable of differentiating into CD163-expressing anti-inflammatory macrophages given appropriate stimuli. Levels of CD163 expression on monocytes may be a potential biomarker reflecting efforts by the immune system to resolve immune activation and inflammation in HIV-infected individuals.

Review of the increased risk of coronary artery disease with HIV-1 infection, association with traditional risk factors, monocyte activation, and impaired cholesterol metabolism. HIV-infected individuals are at increased risk of coronary artery disease (CAD) with underlying mechanisms including chronic immune activation and inflammation secondary to HIV-induced microbial translocation and low-grade endotoxemia; direct effects of HIV and viral proteins on macrophage cholesterol metabolism; and dyslipidemia related to HIV infection and specific antiretroviral therapies. Monocytes are the precursors of the lipid-laden foam cells within the atherosclerotic plaque and produce high levels of proinflammatory cytokines such as IL-6. The minor CD14+/CD16+ “proinflammatory” monocyte subpopulation is preferentially susceptible to HIV infection and may play a critical role in the pathogenesis of HIV-related CAD. In this review, the central role of monocytes/macrophages in HIV-related CAD and the importance of inflammation and cholesterol metabolism are discussed.