Microbiology

Microbiology Study Guide

4.4 Disorders of the Immune System Hypersensitivity Reactions The immune system is likely to have a number of human disorders, known as hypersensitivities. At this stage, the immune system becomes sensitive to the cellular factors or antibodies. Disorders happen when the antibody or cell-mediated immunity fails and is known as an immunodeficiency . The role of the immune system is to protect the body from microorganisms and the infections they cause. If the immunity becomes over-reactive or works in excess, the development of a hypersensitivity reaction takes place, which triggers injury or even death. The ill effects of hypersensitivities, like injuries, occur upon the interaction of antigens with the antibodies or sensitized T-lymphocytes. Immediate hypersensitivity takes place when the reaction of antigens connects with antibodies, while delayed hypersensitivity takes place when the reaction occurs with T-lymphocytes. The outcomes of immediate hypersensitivity involve the development of allergies, cytotoxic reactions, and immune complex reactions. Outcomes of delayed hypersensitivity involve contact dermatitis or an infection allergy. Type I Anaphylactic Hypersensitivity Anaphylaxis , or type I hypersensitivity, is a whole body, immediate hypersensitivity also known as anaphylactic shock . In this case, allergens enter body tissues in the form of a concentration (injections). Once the dosage has been administered, the IgE type of immunity is generated by the plasma cells. The antibodies then travel in the bloodstream and thereby attach at the Fc of the antibody molecule and basophils in the blood. Once the reaction between the antigen and antibody occurs, then histamine and serotonin, which are physiologically active substances, are released from granules within the cell. Allergic reactions are likely to occur, which are referred to as localized anaphylaxis. These localized reactions are induced by foods, pollen grains, and animal dander. Type II Cytotoxic Hypersensitivity Cytotoxic reactions are a form of immediate hypersensitivity, sometimes referred to as type II hypersensitivity . When the antigens react with antibodies in the bloodstream, the immunity types IgE and IgM are generated. These reactions also take place on the surface of the cells of the human body. The output of this reaction is the activation of the complement system, which destructs local tissue cells. For instance, with thrombocytopenia, the antibodies unite with the antigens on the thrombocytes surface and then the complement gets activated. This is when the destruction of thrombocytes takes place. This results in an impaired blood-clotting mechanism. These reactions are apparent by the transfusion reaction that happens with the improper transfusion of blood.

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