Garlic promotes proper immune system function by stimulating certain types of white blood cells, including: macrophages, lymphocytes, natural killer (NK) cells, and eosinophils and the dendritic cells that are messengers among them. These components of the immune system regulate inflammatory proteins called cytokines. With the balancing of these opposing immune system devices, inflammation is kept under control. (9)
Immunoregulation is significant in the context of autoimmune and inflammatory diseases, such as rheumatoid arthritis and cancer. Organosulfur compounds in garlic (and other members of its plant family like onions and leeks) are what give garlic its pungent smell. In the wild, they act as a defense against predators: when a garlic bulb is damaged (i.e., cut or smashed), a chemical reaction ensues that gives off a strong smell to scare away the perpetrator. It’s this same chemical reaction that stimulates the defensive reaction of human immune cells.
The anti-inflammatories and antioxidants in garlic counteract inflammation that is the precursor to cancer. It’s been found that administration of garlic to mice before and during induced cancer inhibits tumor development and growth. (10)