Clinical hypertension is associated with raised serum IgG antibodies. However, whether antibodies are causative agents in hypertension remains unknown. We investigated whether hypertension in mice is associated with B-cell activation and IgG production and moreover whether B-cell/IgG deficiency affords protection against hypertension and vascular remodeling. Angiotensin II (Ang II) infusion (0.7 mg/kg per day; 28 days) was associated with (1) a 25% increase in the proportion of splenic B cells expressing the activation marker CD86, (2) an 80% increase in splenic plasma cell numbers, (3) a 500% increase in circulating IgG, and (4) marked IgG accumulation in the aortic adventitia. In B-cell-activating factor receptor-deficient (BAFF-R(-/-)) mice, which lack mature B cells, there was no evidence of Ang II-induced increases in serum IgG. Furthermore, the hypertensive response to Ang II was attenuated in BAFF-R(-/-) (Δ30±4 mm Hg) relative to wild-type (Δ41±5 mm Hg) mice, and this response was rescued by B-cell transfer. BAFF-R(-/-) mice displayed reduced IgG accumulation in the aorta, which was associated with 80% fewer aortic macrophages and a 70% reduction in transforming growth factor-β expression. BAFF-R(-/-) mice were also protected from Ang II-induced collagen deposition and aortic stiffening (assessed by pulse wave velocity analysis). Finally, like BAFF-R deficiency, pharmacological depletion of B cells with an anti-CD20 antibody attenuated Ang II-induced hypertension by ≈35%. Hence, these studies demonstrate that B cells/IgGs are crucial for the development of Ang II-induced hypertension and vessel remodeling in mice. Thus, B-cell-targeted therapies-currently used for autoimmune diseases-may hold promise as future treatments for hypertension.

Macrophages accumulate in blood vessels during hypertension. However, their contribution to vessel remodeling is unknown. In the present study, we examined the polarization state of macrophages (M1/M2) in aortas of mice during hypertension and investigated whether antagonism of chemokine receptors involved in macrophage accumulation reduces vessel remodeling and blood pressure (BP). Mice treated with ANG II (0.7 mg·kg(-1)·day(-1), 14 days) had elevated systolic BP (158 ± 3 mmHg) compared with saline-treated animals (122 ± 3 mmHg). Flow cytometry revealed that ANG II infusion increased numbers of CD45(+)CD11b(+)Ly6C(hi) monocytes and CD45(+)CD11b(+)F4/80(+) macrophages by 10- and 2-fold, respectively. The majority of macrophages were positive for the M2 marker CD206 but negative for the M1 marker inducible nitric oxide synthase. Expression of other M2 genes (arginase-1, Fc receptor-like S scavenger receptor, and receptor-1) was elevated in aortas from ANG II-treated mice, whereas M1 genes [TNF and chemokine (C-X-C motif) ligand 2] were unaltered. A PCR array to identify chemokine receptor targets for intervention revealed chemokine (C-C motif) receptor 2 (CCR2) to be upregulated in aortas from ANG II-treated mice, while flow cytometry identified Ly6C(hi) monocytes as the main CCR2-expressing cell type. Intervention with a CCR2 antagonist (INCB3344; 30 mg·kg(-1)·day(-1)), 7 days after the commencement of ANG II infusion, reduced aortic macrophage numbers. INCB334 also reduced aortic collagen deposition, elastin loss, and BP in ANG II-treated mice. Thus, ANG II-dependent hypertension in mice is associated with Ly6C(hi) monocyte and M2 macrophage accumulation in the aorta. Inhibition of macrophage accumulation with a CCR2 antagonist prevents ANG II-induced vessel fibrosis and elevated BP, highlighting this as a promising approach for the future treatment of vessel remodeling/stiffening in hypertension.

It has long been known that circulating levels of IgG and IgM antibodies are elevated in patients with essential and pregnancy-related hypertension. Recent studies indicate these antibodies target, and in many cases activate, G-protein coupled receptors and ion channels. Prominent among these protein targets are AT1 receptors, α 1-adrenoceptors, β 1-adrenoceptors, and L-type voltage operated Ca2+ channels, all of which are known to play key roles in the regulation of blood pressure through modulation of vascular tone, cardiac output, and/or Na+/water reabsorption in the kidneys. This suggests that elevated antibody production may be a causal mechanism in at least some cases of hypertension. In this brief review, we will further describe the protein targets of the antibodies that are elevated in individuals with essential and pregnancy-related hypertension and the likely pathophysiological consequences of antibody binding to these targets. We will speculate on the potential mechanisms that underlie elevated antibody levels in hypertensive individuals and, finally, we will outline the therapeutic opportunities that could arise with a better understanding of how and why antibodies are produced in hypertension.

BackgroundM2 macrophages contribute to vascular fibrosis and stiffening in hypertension (Moore et al., 2015). A potential mediator of these actions is the macrophage‐derived, pro‐fibrotic chemokine, chemokine (C‐C motif) ligand 18 (CCL18), which signals via its cognate chemokine receptor, CCR8. Pro‐fibrotic actions of CCL18 have been reported in the lung (Atamas et al., 2003), yet whether these effects are also observed in the heart and vasculature remains to be seen. In addition, the localisation and expression of CCR8 in the vascular wall has not been investigated.AimsTo (i) determine if angiotensin II augments CCL18 production from human primary M2 macrophages,(ii) identify vascular targets of CCL18 and (iii) investigate the ability of CCL18 to promote fibrosis.MethodsHuman primary macrophages were treated with the M2‐polarising stimulus, interleukin‐4 (IL‐4; 0.05–50 ng/ml, 6–72 h) and CCL18 expression was measured (qRT‐PCR, ELISA). Following incubation with a sub‐maximal concentration of IL‐4 (0.5 ng/ml, 24 h), angiotensin II (100 pM) was added for a further 48 h in the presence or absence of the angiotensin II type 1 receptor (AT1R) antagonist, candesartan (1 μM), and effects on CCL18 expression were measured. Blood pressures of saline or angiotensin II (0.7 mg/kg/d, 28 d; s.c.)‐treated male C57BL/6J mice were measured by tail cuff. Localisation and expression of CCR8 and the murine functional analogue of CCL18, CCL8, were assessed in the thoracic aorta by immunohistochemistry and qRT‐PCR, respectively. Type 1 collagen was measured via western blotting in CCL18 (3–300 ng/ml, 72 h)‐treated human cardiac fibroblasts.ResultsIL‐4 caused concentration‐ and time‐dependent increases in macrophage CCL18 mRNA (up to 1700‐fold, P<0.05, n=4–7) and protein (up to 500‐fold, P<0.05, n=5–7) expression. In M2‐polarised macrophages (0.5 ng/ml IL‐4), angiotensin II increased CCL18 protein levels by a further 40% (P<0.05, n=5), an effect which was partially attenuated by candesartan. In aortas from hypertensive mice, CCL8 mRNA expression was elevated by 3‐fold (p<0.05, n=4–8), and the chemokine was found to co‐localise with the M2 macrophage marker CD206. Importantly there was a 50% increase in the number of CCL8+ M2 macrophages in the aorta of hypertensive versus normotensive mice (P<0.05, n=6). CCR8 was also expressed in the endothelium, adventitia and perivascular fat of hypertensive vessels. Finally, treatment of human cardiac fibroblasts with CCL18 increased pro‐ and mature type 1 collagen expression by up to 4‐fold and 1.5‐fold respectively (n=4).ConclusionsAngiotensin II increases CCL18 generation from M2 macrophages, which may target CCR8 expressing endothelial, adventitial and/or perivascular fat cells to promote fibrosis and vascular stiffening. CCL18 also promotes collagen synthesis from human cardiac fibroblasts. Thus, CCL18 and its receptor CCR8, may serve as potential targets for the treatment of vascular and cardiac fibrosis during hypertension.Support or Funding InformationNHMRC Project Grant APP1041326