Dual opposing roles of adaptive immunity in hypertension

Abstract

Hypertension involves remodelling and inflammation of the arterial wall. Interactions between vascular and inflammatory cells play a critical role in disease initiation and progression. T effector and regulatory lymphocytes, members of the adaptive immune system, play contrasting roles in hypertension. Signals from the central nervous system and the innate immune system antigen-presenting cells activate T effector lymphocytes and promote their differentiation towards pro-inflammatory T helper (Th) 1 and Th17 phenotypes. Th1 and Th17 effector cells, via production of pro-inflammatory mediators, participate in the low-grade inflammation that leads to blood pressure elevation and end-organ damage. T regulatory lymphocytes, on the other hand, counteract hypertensive effects by suppressing innate and adaptive immune responses. The present review summarizes and discusses the adaptive immune mechanisms that participate in the pathophysiology in hypertension.

Keywords: Adaptive immunity; Blood pressure; Cytokines; Inflammation; T effector lymphocytes; T regulatory lymphocytes.

Figure 1

Differentiation of naïve T lymphocytes into various subsets in a normal immune response. Antigen-presenting cells (dendritic cells and monocyte/macrophages) present antigens on major histocompatibility complex (MHC)-II to naïve T cells (T_h0) in secondary lymphoid tissues, leading to T-cell clonal expansion and differentiation into effector T cells, such as T helper (T_h)1, T_h2, and T_h17 or T regulatory (T_reg) cells according to combined stimulation by different cytokines. T_h effector lymphocytes and Tregs migrate into tissues such as the vasculature, particularly at the level of the adventitia and perivascular fat. The effector lymphocytes (T_h1 and T_h17) cells activate other immune cells and participate in inflammation by producing pro-inflammatory cytokines such as interferon-γ, interleukin (IL)-6, and IL-17. T regulatory lymphocytes suppress innate and adaptive responses via production of anti-inflammatory cytokines IL-10 and transforming growth factor-β. CD, cluster of differentiation; DC, dendritic cell; MΦ, macrophage; NK cell, natural killer cell; T_c, cytotoxic T cell; TCR, T-cell receptor.

Figure 2

Proposed role of T effector and regulatory lymphocytes in hypertension. Slight elevation in blood pressure (BP) in response to hypertensive stimuli (angiotensin II, aldosterone, endothelin-1, salt and genetic susceptibility) occurs due to increased central signalling, perhaps causing mild tissue injury and formation of damage-associated molecular patterns (DAMPs) and neoantigens. This may lead to activation of innate antigen-presenting cells (APCs) and, subsequently, activation and polarization of naïve CD4⁺ T effector lymphocytes (T_h0) towards pro-inflammatory T helper (T_h)1/T_h17 phenotypes. T_h1/T_h17 may contribute to vascular and kidney damage via production of reactive oxygen species (ROS), interferon (IFN)-γ and interleukin (IL)-17 and lead to maintenance of hypertension and progression of end-organ damage. T regulatory lymphocytes counteract hypertension and associated injury by producing IL-10 or by other mechanisms, and suppression of innate and adaptive immune responses. CD, cluster of differentiation; CNS, central nervous system; MHC-II, major histocompatibility complex-II; PAMPs, pathogen-associated molecular patterns; TCR, T-cell receptor.