MODULE SUPPLEMENT: IMMUNE SYSTEM
The Macrophage

Granulocytes and monocytes/macrophages are considered key effector cells of the defense system, and are likened to "Attilla the Hun" by Isbister in that they deploy a wide range of weapons that tend to be very non-selective in their attack--including oxidizing agents. (Isbister, 1994).

(Also see the Free Radical Theory of Aging--note: this link will open in a new browser window which you can close to return here.)

When phagocytic cells are stimulated there is a marked change in how they handle oxygen--rates of oxygen uptake are increased significantly and produce large amounts of superoxide which, while potent in itself, is then rapidly converted to hydrogen peroxide and hydroxyl radical which is even more potent in its impact (Groer, 2001). This process is called the "Respiratory Burst." With the "Respiratory Burst," the cell protects itself with the presence of lots of potent protective enzymes such as Superoxide dismutase, but of note is that some data suggest that with aging the respiratory burst is less effective and there is greater production of the toxic products and less of some of the protective enzymes (or detoxification mechanisms). Data also indicate that the macrophage becomes somewhat less effective with age, although this may be site specific and data are often conflicting (Lloberas & Celada, 2002). Thus, the reactive oxygen substances can accumulate in the cells.