The Effects of Catecholamines on the Immune System in Particularly the Effects They Have on T-Helper Lymphocytes

Topics: Immune system, T helper cell, Humoral immunity Pages: 9 (3198 words) Published: October 25, 2012
The effects of catecholamines on the immune system in particularly the effects they have on T-helper lymphocytes The immune system is a vast and versatile collection of cells within the human body. These cells prevent the spread of infections, viruses and bacteria throughout the entire body and help in maintaining a healthy lifestyle. The immune system can be affected in many ways with a variety of substances up or down regulating its ability to function correctly. Catecholamines which are found in varying quantities are one such substance. Catecholamines are commonly known as the “flight or fright” hormone and are chemical compounds derived from the amino acid tyrosine (Elenkov et al, 2000) and act as hormones and neurotransmitters. Catecholamine is a collective name for the three main molecules known as adrenaline, noradrenaline and dopamine. The stimulation of the central nervous system results in the direct activation of its two major outflow systems which subsequently regulate the release of catecholamines and cortisol. These 2 systems, the hypothalamic-pituitary-adrenal axis (HPA-axis) and the sympathetic nervous system (SNS) (Smith, 2003), can activate one another and are often triggered by circulating cytokines within the blood. The more important of the two systems, SNS, regulates catecholamines and excitation causes the release of the two most important compounds adrenaline from the adrenal medulla and noradrenaline from the sympathetic nerve terminals. This produces an elevated arterial plasma concentration of both hormones which is thought to occur in a linear fashion with the duration and intensity of exercise performed (Pedersen and Hoffman-Goetz, 2000). Catecholamines released due to the excitation of the SNS affect lymphocytes, monocytes, macrophages and granulocytes each to a varying degree. These changes in immune cells subsequently cause a change in cellular trafficking, proliferation, antibody production and cytokine secretion and activity (Padgett and Glaser, 2003). When released adrenaline and noradrenaline circulate within the blood and express their effects on immune species which express adrenergic receptors on their surface (Pedersen and Hoffman-Goetz, 2000). These receptors are known as α- and β- receptors. The majority of immune cells (T and B lymphocytes, NK cells, macrophages and neutrophils) which are vital to immune function express β2-adrenergic receptors on their surface. Without the presence of the receptor many immune cells would not be able to instigate an immune reaction and therefore during times of heightened adrenaline and noradrenaline immune function would not be as effective. Adrenaline and noradrenaline are known to have either direct or indirect effects on the redistribution of immune cells during exercise and stress. They indirectly cause mobilisation of immune cells by causing demargination of lymphocytes from the vascular endothelium. This effect is brought about by the release of noradrenaline from the SNS which causes an increase in heart rate and blood pressure which consequently causes an increase in shear stress through the blood vessel (Blannin, 2006). When adrenaline is released from the adrenal medulla it acts directly on the immune cells themselves. Adrenaline binds to the β2-adrengenic receptors on many lymphocytes subclasses and directly leads to alteration in its cellular function (Blannin, 2006). It was previously thought that catecholamines had immunosuppressive effects and during physical or psychological stress the increase in these substances blunted the body's ability to combat infection. Previous literature from the 1970s and 1980s (Calcagni and Elenkov, 2006) has provided evidence that catecholamines cause lymphocytopenia, inhibit lymphocyte cytotoxicity and decrease the secretion of certain cytokines. However more recent literature contradicts this, stating that catecholamine could influence the immune system in a positive way (Padgett and Glaser, 2003)....
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