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.