R ecent data suggest that hypertension and hypertensive end-organ damage are not only mediated by hemodynamic injury but also by innate and adaptive immune responses. 1 In their seminal article, Guzik et al 2 were able to show that RAG-1 -/-mice that lack T and B cells have attenuated hypertension in response to angiotensin II (Ang II) infusion. This finding was confirmed in SCID mice. 3 In 2005, a novel T-helper cell subset (Th17) producing interleukin 17 (IL-17) was discovered.4 IL-17 is a proinflammatory cytokine secreted by innate and adaptive immune cells. Although the source of IL-17 is restricted to hematopoietic cells, the IL-17 receptor is widely expressed. Th17 cells need interleukin 23 (IL-23) for expansion and survival. IL-23 is secreted by activated dendritic cells and macrophages. The potential function of Th17 cells in autoimmune disease was first shown in IL-23p19-deficient mice. IL-23p19 knockout animals demonstrated a substantial decrease in Th17-polarized cells and were resistant to the development of experimental autoimmune encephalomyelitis, 5 experimental induction of multiple sclerosis, and rheumatoid arthritis. A new link between cardiovascular disease and IL-17 has been proposed by recent data showing that increased dietary salt intake drives autoimmune diseases through the induction of Th17 cells. C57black mice are resistant to hypertensive end-organ damage. 7 We recently showed that combining deoxycorticosterone acetate (DOCA) salt and Ang II infusion induces substantial hypertensive renal and cardiac injury. 8 This model has been successfully used to evaluate the role of chemokine receptors and ADMA (asymmetric dimethylarginine) in hypertensive end-organ damage.

Adaptive and innate immune responses contribute to hypertension and hypertensive end-organ damage. Here, we determined the role of anaphylatoxin C5a, a major inflammatory effector of the innate immune system that is generated in response to complement activation, in hypertensive end-organ damage. For this purpose, we assessed the phenotype of C5a receptor 1 (C5aR1)-deficient mice in ANG II-induced renal and cardiac injury. Expression of C5aR1 on infiltrating and resident renal as well as cardiac cells was determined using a green fluorescent protein (GFP)-C5aR1 reporter knockin mouse. Flow cytometric analysis of leukocytes isolated from the kidney of GFP-C5aR1 reporter mice showed that 28% of CD45-positive cells expressed C5aR1. Dendritic cells were identified as the major C5aR1-expressing population (88.5%) followed by macrophages and neutrophils. Using confocal microscopy, we detected C5aR1 in the kidney mainly on infiltrating cells. In the heart, only infiltrating cells stained C5aR1 positive. To evaluate the role of C5aR1 deficiency in hypertensive injury, an aggravated model of hypertension was used. Unilateral nephrectomy was performed followed by infusion of ANG II (1.5 ng·g(-1)·min(-1)) and salt in wild-type (n = 34) and C5aR1-deficient mice (n = 32). C5aR1-deficient mice exhibited less renal injury, as evidenced by significantly reduced albuminuria. In contrast, cardiac injury was accelerated with significantly increased cardiac fibrosis and heart weight in C5aR1-deficient mice after ANG II infusion. No effect was found on blood pressure. In summary, the C5a:C5aR1 axis drives end-organ damage in the kidney but protects from the development of cardiac fibrosis and hypertrophy in experimental ANG II-induced hypertension.

Myeloperoxidase (MPO) is an enzyme expressed in neutrophils and monocytes/macrophages. Beside its well-defined role in innate immune defence, it may also be responsible for tissue damage. To identify the role of MPO in the progression of chronic kidney disease (CKD), we investigated CKD in a model of renal ablation in MPO knockout and wild-type mice. CKD was induced by 5/6 nephrectomy. Mice were followed for 10 wk to evaluate the impact of MPO deficiency on renal morbidity. Renal ablation induced CKD in wild-type mice with increased plasma levels of MPO compared with controls. No difference was found between MPO-deficient and wild-type mice regarding albuminuria 1 wk after renal ablation, indicating similar acute responses to renal ablation. Over the next 10 wk, however, MPO-deficient mice developed significantly less albuminuria and glomerular injury than wild-type mice. This was accompanied by a significantly lower renal mRNA expression of the fibrosis marker genes plasminogen activator inhibitor-I, collagen type III, and collagen type IV as well as matrix metalloproteinase-2 and matrix metalloproteinase-9. MPO-deficient mice also developed less renal inflammation after renal ablation, as indicated by a lower infiltration of CD3-positive T cells and F4/80-positive monocytes/macrophages compared with wild-type mice. In vitro chemotaxis of monocyte/macrophages isolated from MPO-deficient mice was impaired compared with wild-type mice. No significant differences were observed for mortality and blood pressure after renal ablation. In conclusion, these results demonstrate that MPO deficiency ameliorates renal injury in the renal ablation model of CKD in mice.

Binding of renin and prorenin to the (pro)renin receptor (PRR) increases their enzymatic activity and upregulates the expression of pro-fibrotic genes in vitro. Expression of PRR is increased in the heart and kidney of hypertensive and diabetic animals, but its causative role in organ damage is still unclear. To determine whether increased expression of PRR is sufficient to induce cardiac or renal injury, we generated a mouse that constitutively overexpresses PRR by knocking-in the Atp6ap2/PRR gene in the hprt locus under the control of a CMV immediate early enhancer/chicken betaactin promoter. Mice were backcrossed in the C57Bl/6 and FVB/N strain and studied at the age of 12 months. In spite of a 25-to 80-fold renal and up to 400-fold cardiac increase in Atp6ap2/PRR expression, we found no differences in systolic blood pressure or albuminuria between wild-type and PRR overexpressing littermates. Histological examination did not show any renal or cardiac fibrosis in mutant mice. This was supported by real-time PCR analysis of inflammatory markers as well as of pro-fibrotic genes in the kidney and collagen in cardiac tissue. To determine whether the concomitant increase of renin would trigger fibrosis, we treated PRR overexpressing mice with the angiotensin receptor-1 blocker losartan over a period of 6 weeks. Renin expression increased eightfold in the kidney but no renal injury could be detected. In conclusion, our results suggest no major role for PRR in organ damage per se or related to its function as a receptor of renin.

The role of CXCR1, also known as fractalkine receptor, in hypertension is unknown. The present study determined the role of the fractalkine receptor CXCR1 in hypertensive renal and cardiac injury. Expression of CXCR1 was determined using CXCR1 mice that express a GFP reporter in CXCR1 cells. FACS analysis of leukocytes isolated from the kidney showed that 34% of CD45 cells expressed CXCR1. Dendritic cells were the majority of positive cells (67%) followed by macrophages (10%), NK cells (6%) and T cells (10%). Using confocal microscopy, the receptor was detected in the kidney only on infiltrating cells but not on resident renal cells. To evaluate the role of CXCR1 in hypertensive end-organ injury an aggravated model of hypertension was used. Unilateral nephrectomy was performed followed by infusion of Ang II (1.5 ng/g/min) and a high salt diet in wildtype (n=15) and CXCR1-deficient mice (n=18). CXCR1-deficiency reduced the number of renal dendritic cells and increased the numbers of renal CD11b/F4/80 macrophages and CD11b/Ly6G neutrophils in Ang II infused mice. Surprisingly, CXCR1-deficient mice exhibited increased albuminuria, glomerular injury and reduced podocyte density in spite of similar levels of arterial hypertension. In contrast, cardiac damage as assessed by increased heart weight, cardiac fibrosis and expression of fetal genes and matrix components was not different between both genotypes. Our findings suggest that CXCR1 exerts protective properties by modulating the invasion of inflammatory cells in hypertensive renal injury. CXCR1 inhibition should be avoided in hypertension because it may promote hypertensive renal injury.

Streptococcus pneumoniae is a leading cause of bacterial pneumonia worldwide. Given the critical role of dendritic cells (DCs) in regulating and modulating the immune response to pathogens, we investigated here the role of DCs in S. pneumoniae lung infections. Using a well-established transgenic mouse line which allows the conditional transient depletion of DCs, we showed that ablation of DCs resulted in enhanced resistance to intranasal challenge with S. pneumoniae. DCs-depleted mice exhibited delayed bacterial systemic dissemination, significantly reduced bacterial loads in the infected organs and lower levels of serum inflammatory mediators than non-depleted animals. The increased resistance of DCs-depleted mice to S. pneumoniae was associated with a better capacity to restrict pneumococci extrapulmonary dissemination. Furthermore, we demonstrated that S. pneumoniae disseminated from the lungs into the regional lymph nodes in a cell-independent manner and that this direct way of dissemination was much more efficient in the presence of DCs. We also provide evidence that S. pneumoniae induces expression and activation of matrix metalloproteinase-9 (MMP-9) in cultured bone marrow-derived DCs. MMP-9 is a protease involved in the breakdown of extracellular matrix proteins and is critical for DC trafficking across extracellular matrix and basement membranes during the migration from the periphery to the lymph nodes. MMP-9 was also significantly up-regulated in the lungs of mice after intranasal infection with S. pneumoniae. Notably, the expression levels of MMP-9 in the infected lungs were significantly decreased after depletion of DCs suggesting the involvement of DCs in MMP-9 production during pneumococcal pneumonia. Thus, we propose that S. pneumoniae can exploit the DC-derived proteolysis to open tissue barriers thereby facilitating its own dissemination from the local site of infection.

A key finding supporting a causal role of the immune system in the pathogenesis of hypertension is the observation that RAG1 knockout mice on a C57Bl/6J background (B6.Rag1 −/ − ), which lack functional B and T cells, develop a much milder hypertensive response to Ang II (angiotensin II) than control C57Bl/6J mice. Here, we report that we never observed any Ang II resistance of B6.Rag1 −/− mice purchased directly from the Jackson Laboratory as early as 2009. B6.Rag1 −/− mice displayed nearly identical blood pressure increases monitored via radiotelemetry and hypertensive end-organ damage in response to different doses of Ang II and different levels of salt intake (0.02%, 0.3%, and 3% NaCl diet). Similarly, restoration of T-cell immunity by adoptive cell transfer did not affect the blood pressure response to Ang II in B6.Rag1 −/− mice. Full development of the hypertension-resistant phenotype in B6.Rag1 −/− mice appears to depend on the action of yet unidentified nongenetic modifiers in addition to the absence of functional T cells.

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