**6. Mechanism of action of antioxidants in improving the immune status of AIDS and TB patients**

Antioxidants are compounds that dispose, scavenge and suppress the formation of free radicals or oppose their actions. Free radicals, primarily the ROS, superoxide and hydroxyl radicals, which are highly reactive, with an unpaired electron in an atomic or molecular orbit, are generated under physiological conditions during aerobic metabolism (Semba & Tang, 1999; Champe *et al*., 2005). Because free radicals are potentially toxic, they normally are inactivated or scavenged by antioxidants before they can damage lipids, proteins or nucleic acids.

Superoxide dismutase (SOD), catalase and glutathione peroxidase (GSH-Px) are the primary antioxidant enzymes involved in the direct elimination of ROS whereas glutathione transferase, glucose-6-phosphate dehydrogenase (G6PD) and copper-binding ceruloplasmin are secondary antioxidant enzymes which assist in maintaining a steady concentration of glutathione and NADPH required for optimal functioning of the primary antioxidant enzymes (Kiremidjian-Schumacher *et al*., 1994; Champe *et al*., 2005). Antioxidant enzymes require micronutrients such as selenium, iron, copper, zinc and manganese as cofactors for optimal catalytic activity and to act as effective antioxidant defence mechanisms. If homeostasis between the rate of formation of free radicals and the rate of neutralization of free radicals is not maintained, oxidative damage, known as oxidative stress occurs which further damages the already compromised immune system and consequently enhances HIV and TB progression (Cunningham-Rundles, 2001; Cunningham-Rundles *et al*., 2005) and it has been reported that most of these antioxidants are derived from dietary sources (fruits and vegetables including red palm oil (Maxwell & Lip, 1997; Ebong *et al*., 1999; Edem, 2002; Van Rooyen *et al*., 2008).
