Free radical immune system function

Selenium is an essential trace element in the human body. This nutrient is an important part of antioxidant enzymes that protect cells against the effects of free radicals that are produced during normal oxygen metabolism. Selenium is also essential for normal functioning of immune system and thyroid gland. 

Nitric oxide and NO synthases. Nitric oxide (NO) is a reactive free radical whose formula is often written as NO to recognize this characteristic. However, NO is not only a toxic and sometimes dangerous metabolite but also an important hormone with functions in the circulatory system, the immune system, and the brain.510 512 The hormonal effects of NO are discussed in Chapter 30, but it is appropriate here to mention a few reactions. Nitric oxide reacts rapidly with 02 to form nitrite (Eq. 18-61). 

When a diet is rich in polyunsaturated fatty acids, the inflammatory response and production of free radicals appear to be strengthened. Arachidonic acid is held responsible for this reaction, as it is used by lipoxygenases of the immune system cells to produce, via biochemical transformations, leukotrienes, compounds which function as mediators and perform an important function in the immune system (Szponar and Respondek 1998, Fimmel and Zouboulis 2005). 

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