Angiotensin II regulates cellular immune responses through a calcineurin-dependent pathway

The renin-angiotensin system (RAS) is a key regulator of vascular tone and blood pressure. In addition, angiotensin II also has a number of cellular e ffects that may contribute to disease pathogenesis. Using Agtr1a(-/-) mice, which lack AT(1A) receptors for angiotensin II, we have identified a novel function of the RAS to modulate the immune system. We find that angiotensi n II, acting through type 1 (AT(1)) receptors on immune cells, triggers the proliferation of splenic lymphocytes. These actions contribute to the vigo r of cellular alloimmune responses. Within lymphoid organs, sufficient comp onents of the RAS are present to activate AT(1) receptors during an immune response, promoting cell growth. These actions require activation of calcin eurin phosphatase. In an in vivo model of cardiac transplantation, the abse nce of AT(1) signaling accentuates the immunosuppressive effects of the cal cineurin inhibitor cyclosporine. We conclude that inhibition of AT(1) recep tor signaling should be useful as an anti-inflammatory and immunosuppressiv e therapy. Furthermore, the actions of the RAS to promote lymphocyte activa tion may contribute to inflammation that characterizes a number of diseases of the heart and the vascular system.