31.6 Diseases that Weaken the Immune System KEY CONCEPT When the immune system is weakened, the body cannot fight off disease.

31.6 Diseases that Weaken the Immune System Leukemia is characterized by abnormal white blood cells. –characterized by immature white blood cells –causes weakened immune system Leukemia is cancer of the bone marrow.

31.6 Diseases that Weaken the Immune System Leukemia leads to opportunistic infections. –occur because white blood cells cannot fight infections –if immune system were healthy, it would fight these infections

31.6 Diseases that Weaken the Immune System HIV targets the immune system. The human immunodeficiency virus (HIV) is a retrovirus. –is transmitted by mixing infected blood with a bodily fluid

31.6 Diseases that Weaken the Immune System HIV infection leads to AIDS. HIV T cell dead T cell antibody activated B cell ---attacks and weakens the immune system –HIV reproduces in and destroys T cells. –The body cannot replace T cells fast enough. –T cells cannot help in immune responses.

31.6 Diseases that Weaken the Immune System AIDS is acquired immune deficiency syndrome. –several opportunistic infections –very low amount of T cells

31.6 Diseases that Weaken the Immune System Page 967 # 1-23 Use notebook paper.