Beta-carotene stimulates many aspects of immunity.

Beta- carotene enhances the activity of T cells and B cells, and boosts the tumor-destroying ability of macrophages, natural-killer cells, and cytotoxic T cells.

Beta-carotene's antioxidant properties compliments the action of vitamin A.

White blood cells use large numbers of free radicals to kill bacteria. After an infection, many of these free radicals can damage healthy cells and DNA, contributing to cardiovascular disease and cancer.

Beta-carotene plays a dual role in immunity.

First, it helps white blood cells produce more free radicals to kill bacteria.

Second, it helps clean up many of the excess free radicals during and after an infection, thereby reducing free radical damage to DNA.

When your health is compromised by infection or other stresses, your immunity is depressed. When this is combined with a low intake of beta-carotene, your immunity may be significantly affected.

In a clinical study, supplemental beta-carotene in high doses (180 milligrams, equivalent to 300,000 IU per day) was found to increase the number of T- lymphocyte "helper" cells in healthy males with normal immune function. T- helper cells are very important immune cells.

There was a 30 percent increase in T-helper cell after only two weeks of supplementation. Researchers have speculated that even more dramatic increases might be achieved among individuals who are immune compromised.

Beta-carotene supplementation, in conjunction with other therapies, may be helpful in AIDS patients and in some cancer patients. Supplements of 60 milligrams (100,000 IU) of beta-carotene daily was found to increase the number of natural-killer cells, which help defend the body.

http://www.holisticonline.com/cancer/Cancer_beta-car-2-nat-rem.htm

http://www.mnwelldir.org/docs/immune/immune2.htm