Immune System and Inflammation in Hypertension

*Mohammed Ibrahim Sadik*

#### **Abstract**

Hypertension is a widely prevalent and a major modifiable risk factor for cardiovascular diseases. Despite the available long list of anti-hypertension drugs and lifestyle modification strategies for blood pressure control, a large number of hypertensive patients fail to achieve adequate blood pressure control even when prescribed a combination of drugs from three or more classes. Thus, identifying and targeting of further mechanisms that underlie hypertension is decisive in alleviating burden of this disorder. In recent decades research have shown that perturbed immune system and inflammation contribute to hypertension. Experimental studies on animal models have shown that immune cells such as dendritic cells, macrophages, and lymphocytes contribute for the development and/or sustaining of hypertension. In hypertension, inflammatory immune cells that infiltrated the kidney cause retention of sodium, renal fibrosis, glomerular injury, and chronic kidney disease, all of them contribute for elevated blood pressure. Similarly, immune cells and inflammatory cytokines are involved in blood vessels structural and functional changes associated with hypertension. Perturbed immune system and chronic low-grade systemic inflammation enhance SNS activity and this contributes to elevated blood pressure by its effect on blood vessels tone, on the kidneys, and on immune system.

**Keywords:** hypertension, immune system, inflammation

## **1. Introduction**

Hypertension is defined as office or clinic systolic blood pressure (SBP) values >140 mmHg and/or diastolic blood pressure (DBP) values >90 mmHg in adult population [1, 2]. It is one of the major modifiable risk factors for cardiovascular diseases (CVDs) [3]. Hypertension is the main risk factor for cardiovascular diseases, especially for coronary heart disease, heart failure, arrhythmia, stroke, peripheral vascular disease, and also for chronic kidney disease and dementia [4]. Globally, in the year 2017, high systolic blood pressure was the leading risk factor of all-cause deaths, accounting for 10.4 million deaths and 218 million disability-adjusted life-years (DALYs), followed by smoking, high fasting plasma glucose (FPG), high body-mass index (BMI), and short gestation for birth weight. Astonishingly, from 1990 to 2017, high SBP was consistently responsible for the largest number of all-cause deaths, followed by smoking and high FPG respectively [5]. In 2010, 31.1% (1.39 billion people) of the world's adults had hypertension [6]. The number of adults with hypertension in 2025 was predicted to be a total of 1.56 billion [7].

Currently, hypertension treatment drugs such as adrenoceptor antagonists (propranolol and prazosin), ACE inhibitors (perindopril), angiotensin receptor blockers (irbesartan), mineralocorticoid antagonists (spironolactone), diuretics (thiazides and amiloride), and vasodilators (nitrates, calcium channel blockers, and hydralazine) are being used to control blood pressure in hypertensive patients [8]. Despite, the presence of a plethora of antihypertensive drugs and lifestyle modification strategies for blood pressure control a large number of hypertensive patients remained undiagnosed or untreated or did not control their blood pressure to target level in spite of being treated [6]. The proportion of hypertensive population that got treatment (55.6% in high-income countries (HIC), 29.0% in low and middle-income countries (LMIC)) and that got their blood pressure controlled (28.4% in HIC, 10.3% in LMIC) is astonishingly low [9]. Moreover, up to 40% of patients with hypertension fail to achieve adequate blood pressure control, even when prescribed a combination of drugs from three or more classes [10]. These observations highlight lack of efficacy of the current hypertension prevention and control strategies and also indicate that in some patients at least, additional drivers of hypertension must exist, and new targets need to be identified and targeted for the treatment of hypertension.

Hypertension is associated with chronic low-grade systemic inflammation [11]. It is hypothesized that perturbation in immune system and chronic low-grade systemic inflammation is one of the contributors in development and/or sustaining of hypertension. Accordingly, this book chapter composed existing evidence to show the contribution of perturbation in immune system and chronic low-grade systemic inflammation to the development and/or sustaining of hypertension.
