Hypersensitivity Case Study

*Poison Ivy- The body's immune system is normally in the business­ of protecting us from bacteria, viruses, and other foreign invaders that can make us sick. But when urushiol from the poison ivy plant touches the skin, it instigates an immune response, called dermatitis, to what would otherwise be a harmless substance. Hay fever is another example of this type of response; in the case of hay fever, the immune system overreacts to pollen, or another plant-produced substance. Here's how the poison ivy response occurs.

Urushiol makes its way down through the skin, where it is metabolized, or broken down. Immune cells called T lymphocytes (or T-cells) recognize the urushiol derivatives as a foreign substance, or antigen. They send out inflammatory signals called cytokines, which bring in white blood cells.

Under orders from the cytokines, these white blood cells turn into macrophages. The macrophages eat foreign substances, but in doing so they also damage normal tissue, resulting in the skin inflammation that occurs with poison ivy.

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­ The allergic reaction to poison ivy is known as delayed hypersensitivity. Unlike immediate hypersensitivity, which causes an allergic reaction within minutes of exposure to an antigen, delayed hypersensitivity reactions don't emerge for several hours or even days after the exposure. Most people don't have a reaction the first time they touch poison ivy, but develop an allergic reaction after repeated exposure. Everyone has a different sensitivity, and therefore a slightly different reaction, to poison ivy. Sensitivity usually decreases with age and with repeat exposures to the plant.

*Transfusing a person of Type A Blood with Type B Blood- ABO blood type system The ABO system consists of A, B, AB, and O blood types. People with type A have antibodies in the blood against type B. People with type B have antibodies in the blood against type A. People with AB have no anti-A or anti-B antibodies. People with type O have both anti-A and anti-B antibodies. People with type AB blood are called universal recipients, because they can receive any of the ABO types. People with type O blood are called universal donors, because their blood can be given to people with any of the ABO types. Mismatches with the ABO and Rh blood types are responsible for the most serious, sometimes life-threatening, transfusion reactions.

So unless the person is RH- there usually isn't that big of a reaction when An Type A is given Type B blood. These reactions may be mild or severe. Most mild reactions are not life-threatening when treated quickly. Even mild reactions, though, can be frightening. Severe transfusion reactions can be life-threatening, but this is very rare. Mild allergic reactions may involve itching, hives, wheezing, and fever. Severe reactions may cause anaphylactic shock.

Exposure to a field of Ragweed- Ragweed allergy, similar to other pollen allergies, may include symptoms of allergic rhinitis, allergic conjunctivitis and allergic asthma. Symptoms caused by ragweed pollen allergy would be expected to start during August and September and last until October or November, depending on the climate. So stay out of a field of Ragweed during those times a year if you experience allergy or hypersensitivity around ragweed.

*Unsuccessful Kidney Transplant- Transplant rejection is when transplanted tissue is rejected by the recipient's immune system, which destroys the transplanted tissue. Transplant rejection can be lessened by determining the molecular similitude between donor and recipient and by use of immunosuppressant drugs after transplant. Hyper-acute rejection occurs a few minutes after the transplant when the antigens are completely unmatched. The tissue must be removed right away so the recipient does not die. This type of rejection is seen when a recipient is given the wrong type of blood. For example, a person given type A blood when he or she is type B.