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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 2 Immune responses as a function of dietary essential fatty acid. Note the broad<br />

<strong>and</strong> imprecise range of EFA adequacy for immune function; in particular, the upper limit of<br />

‘‘normal’’ EFA varies for different immune functions<br />

estimated that 80% of mobile leukocytes are normally sequestered in organs of the<br />

RES, while the remainder float in the bloodstream.<br />

Functionally, the components of the immune system are often divided into<br />

response elements. That is, humoral (or circulating) <strong>and</strong> cell-mediated immunity are<br />

the most commonly used concepts for describing immune functions, although there<br />

is communication between these facets of immune cells via a variety of soluble<br />

products called cytokines. In addition to the distinctions of humoral <strong>and</strong> cell-mediated<br />

immunity, a number of other components of the immune system play a role in<br />

protecting against pathogenic organisms. These include the polymorphonuclear leukocytes,<br />

which are divided into neutrophils, basophils, <strong>and</strong> eosinophils based on their<br />

staining characteristics in a smear of blood treated with Giemsa or Wright’s stain.<br />

Neutrophils participate in acute inflammatory reactions against bacteria <strong>and</strong> other<br />

foreign bodies. Basophils <strong>and</strong> eosinophils are components of allergic reactions.<br />

Eosinophils are elevated also in response to parasitic infections.<br />

There is a wide range of normal immune functions <strong>and</strong> a wide range of normal<br />

numbers of circulating immune cells. For example, the normal range of leukocytes<br />

in the blood of humans is 5000 to 10,000/mm 3 . Within this range there are no<br />

discernible differences in susceptibility to infection. In fact, there is little increased<br />

risk of infection unless total white blood cells drop below 1000/mm 3 .<br />

Functional terms used to describe the immune system include natural (innate)<br />

<strong>and</strong> specific (acquired). Natural immunity is a result of molecules such as cytokines<br />

Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.

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