Since each of the antigens exists, in different individuals, in as many as 20 varieties, the number of possible HLA types is about 10,000. The genes that encode the HLA antigens, located on chromosome 6, are the subject of intense research. When normal cells turn into cancer cells, some of the antigens on their surface change. These new or altered antigens flag immune defenders, including cytotoxic T cells, natural killer cells, and macrophages. According to one theory, patrolling cells of the immune system provide continuing bodywide surveillance, spying out and eliminating cells that undergo malignant transformation.
Tumors develop when the surveillance system breaks down or is overwhelmed.
A new approach to cancer therapy uses antibodies that have been specially made to recognize specific cancer. When coupled with natural toxins, drugs, or radioactive substances, the antibodies seek out their target cancer cells and deliver their lethal load. Alternatively, toxins can be linked to a lymphokine and routed to cells equipped with receptors for the lymphokine. The Immune System and the Nervous System Biological links between the immune system and the central nervous system exist at several levels. In addition, networks of nerve fibers have been found to connect directly to the lymphoid organs.