Microbiology

Microbiology Study Guide

Type III Immune Complex Hypersensitivity This type of hypersensitivity is the result of the combination of the antibodies and antigens that result in fixation of the complement. Antigens are in the form of fluid solutions that react with the antibodies of type IgM or IgG. In this case, the nucleic acids or proteins are also involved. For instance, in the case of serum sickness, the serum of the animals is injected to the human body and in this event, the proteins obtain the antibody production. When the reaction between the antibody and antigen takes place, immune complexes are formed and activated, which leads to the destruction of body tissues. Symptoms of this hypersensitivity are edema of the organs like the face, hands, and feet, and interference with normal functioning of the respiratory system. Instances of the diseases due to type III immune complex hypersensitivity include systemic lupus erythematosus, rheumatoid arthritis, and glomerulonephritis. Type IV Cellular Hypersensitivity In this type of hypersensitivity, the immune cells T-lymphocytes participate instead of the antibodies. Lymphokines are generated by these T-cells, which initiate the macrophages; the final result is phagocytosis. In this case, the immune system gets aggravated and the phagocytes cause the destruction of the tissues of the body. This form of hypersensitivity is also known as delayed hypersensitivity, as the time taken to develop the reaction between antigens and T-cells are as long as a day or more. One of the major symptoms of this hypersensitivity is the development of infection allergy. For instance, in the case of a tuberculin skin test, superficial application of the purified protein derivative (PPD) of Mycobacterium tuberculosis is done and then after the lapse of one or two days, the reaction on the skin takes place if the person experienced any previous episode of tuberculosis. Immune Deficiency Disease Deficiencies contribute towards a possible disorder of the immune system itself. These disorders can be congenital or iatrogenic, or due to any malignancy in the lymphatic system. For instance, abnormalities of the B-cells of the immune system lead to immunodeficiency and, in this case, the antibodies produced are not normal. The triggers for these disorders may be due to liver diseases, systemic lupus, erythematosus, etc. Another instance of immune deficiency disease is multiple myeloma, in which an excess of antibodies is generated by the clones of B-cells; these are then secreted in urine and are called Bence Jones proteins. B-cells reduce and form lesser antibodies, called hypogammaglobulinemia, which may be due to a gene defect or a disorder of bone marrow. Another possible abnormality is the inability of the T-lymphocytes to initiate cell-mediated immunity. This condition is termed as DiGeorge's syndrome and results from the improper formation or absence of thymus gland. In this case, the person is highly prone to getting infections from fungi, viruses, and protozoa.

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