Immune System Diseases

1. Immune system sometimes respond to harmless foreign substances as if they were pathogens
2. Sometimes mistakes self for pathogens and attacks own body cells
3. Certain diseases can also attack and damage immune system so it loses ability to defend body
4. Allergies
• immune system makes inflammatory response to harmless antigen
• antigen that causes allergic reaction is an allergen
• allergies vary from person to person
• tendency to develop allergies are inherited
5. Severity of allergies
• symptoms caused by release of histamines, chemicals that stimulate inflammation
• ranges from scarcely noticeable to fatal
• typical symptoms: itchy eyes, sneezing, and skin rashes
• uncomfortable but not life-threatening
• usually treated with antihistamines
• immunotherapy ("allergy shots") are recommended for more severe allergies
• injected with larger and larger amounts over the years
• desensitizes immune system
• reduces severity of allergy or eliminates it altogether
• most severe allergic reaction: anaphylaxis
• massive release of histamines
• causes collapse of circulatory system and constriction of breathing passages
• likely to b fatal if without emergency treatment
• injection of epinephrine treatment
• suppresses non-emergency body processes
1. including immune response
6. Immediate hypersensitivity reaction
• when exposure to antigen causes immediate allergy symptoms
• called immediate hypersensitivity reaction
• humoral immune response
• anaphylaxis may occur if allergy is severe
• affects mainly mucous membranes lining nose
• usually runny nose and nasal congestion
• pollen most common cause of allergic rhinitis
• also called hay fever, but pollen is most likely cause
7. Delayed hypersensitivity reaction
• antigen causes allergy symptoms hours or days after exposure
• cell-mediated immune response
• rashes may develop
8. Autoimmune diseases
• immune system fails to recognize body's own molecules and attack's own body cells
• ex: rheumatoid arthritis, type 1 diabetes mellitus, multiple sclerosis and systemic lupus erythematosis
• currently incurable
• treatment can help relieve symptoms and prevent long-time damage
• causes are unknown
• one way it may develop: molecular mimicry
• pathogens bearing similar antigens to person's own molecules
• immune system mounts attack, but also attack own cells
9. Acquired immunodeficiency
• immune function declines person who was born with normal immune system
• causes: 
• age: older people have a less effective immune system
• obesity
• alcoholism
• illegal drug abuse
• malnutrition in some third world countries
• medications can interfere with normal immune function
• immune suppressive drugs are deliberately given to people with autoimmune diseases and transplanted organs
• immune suppression can be a side effect
• chemotherapy
• cancer cells attack immune system cells
10. HIV transmission
• transmitted through direct contact of mucous membranes or bloodstream with body fluids that contain HIV
• body fluids: blood, semen, vaginal fluid, preseminal fluid, and breast milk
• transmission can occur through sexual contact or contaminated hypodermic needles
• in the past, transmitted through blood transfusions
• blood now screened for HIV, so it is no longer transmitted this way
11. HIV and the immune system
• HIV destroys helper T cells
• proteins on virus coat allows it to fuse with host's helper T cells
• injects own DNA into helper T cells and uses T cell's "machinery" to make copies of itself
• virus copies destroys cells in process of reproducing
• copies go to infect other helper T cells throughout body
• first several weeks, immune system will attempt to fight off virus
• at first, reduces number of virus copies in blood
• immune system unable to destroy virus
• virus continues to multiply in lymphatic system
• HIV avoids immune system by: 
• undergoing frequent mutations to keep changing antigens, so antigen-specific lymphocytes cannot develop to destroy virus
• virus uses host's membrane to cover up viral antigens to escape detection
• helper T cells continue to decline in the blood and copies of virus keep increasing
• helper T cells declining means immune response is weakened
• treatment can only slow down he increase of virus copies
• still no cure for HIV infection or AIDS, and no vaccine to prevent infection
• field of intense study by biomedical scientists
12. AIDS
• collection of symptoms and diseases
• result of years of damage to immune system by HIV
• AIDS diagnosed when helper T cells fall to very low levels
• opportunistic diseases also develop
• penumocytis pneumonia and Kaposi's cancer
• called opportunistic because the viruses take the "opportunity" to infect someone with damaged immune system
• often direct cause of death of someone with AIDS
• AIDs first identified in 1981