Hypersensitivity Reaction Essay Example | Topics and Well Written Essays - 1250 words

Hypersensitivity Reaction - Essay Example Hypersensitivity Reaction This paper aims to review the immunological mechanisms giving rise to the four groups of hypersensitivity. It also compares and contrasts hypersensitivity reactions caused by antibodies and those caused by T-lymphocytes, while also discussing the clinical consequences of each of the reactions using examples. Hypersensitivity reactions can be divided into type I-IV, based on the various involved mechanisms. Type I, often associated with allergy, is mediated by IgE. IgE triggers basophil and mast cell degranulation cross linking with antigen. Type II occurs on binding of the host’s cells to antigens, which marks them for destruction (Phillips, 2006 p89). Mediation is by IgG and IgM antibodies. Type III hypersensitivity triggering occurs due to aggregates of IgM, IgG, complement proteins, and antigens deposited in tissues. Type IV hypersensitivity’s mediation is by macrophages, monocytes, and T cells. Infectious diseases and autoimmune involve this hypersensitivity in thei r reactions. Most hypersensitivity injuries develop due to interactions between antibodies and antigens or between sensitized T-lymphocytes and antigens. The general symptoms  accompanying the reaction depend on the involvement of either T-lymphocytes, or antibodies. During antibody involvement, immediate hypersensitivity results, while T-lymphocyte involvement results in delayed hypersensitivity reaction. Immediate hypersensitivity includes immune complex reactions, cytotoxic reactions, allergic reactions, and anaphylaxis. Delayed hypersensitivity includes infection allergies and contact dermatitis. Antibody Mediated Hypersensitivity vs. T-lymphocyte Mediated Hypersensitivity Antibody mediated hypersensitivity depends on the antigen nature, its frequency, and antigen contact route (Phillips, 2006 p11). It also depends on antibody type that reacts with the antigen. The initial antigen dose is known as sensitizing dose. On exposure, a latent period follows. Later, a dose of the sam e antigen, referred to as shocking or eliciting dose, sets off the reaction. This results in tissue damage. In T-lymphocyte mediated hypersensitivity, T-lymphocytes function rather than antibodies. These T-lymphocytes function in cell mediated immunity. They produce Lymphokines, which stimulate macrophage influx in order to perform phagocytosis. This results in immune response exaggeration. For both antibody mediated and T-lymphocyte mediated hypersensitivity reactions, local tissue destruction results. However, destruction of tissue by T-lymphocyte mediation occurs via phagocytosis. For antibody mediated hypersensitivity, reactions begin minutes after antigen administration (Phillips, 2006 p31). On direct administration of the antigen directly to the tissue, for example, injection or bee stings, a systemic reaction occurs. For instance, anaphylactic shock may result. When the contact involved is superficial, involving epithelial tissue, a localized reaction results, for example, ha y fever and asthma. These reactions can also be referred to as atopy or allergy. T-lymphocyte mediated hypersensitivity, on the other hand, requires one day or more in order to develop. It can manifest in the form of infection allergy, such as in the tuberculin test (Phillips, 2006 p34). A second manifestation of T-lymphocyte mediated hypersensitivity is contact dermatitis. Large blister like lesions accompany the reaction, with vesicles surrounded by redness. The vesicles usually itch intensely.