Slides Pathology-2 SU (4).ppt.pdf

Dr. Mohammed Abdellah General Pathology-2 sinaiuniversity. net • DISORDERS OF IMMUNE REACTION By the end of lecture you should be able to understand: . -DISORDERS OF IMMUNE REACTION. Definitions Antigen: a foreign protein that can evoke an immune response mediated by B (plasma cells) or T lymp...

Dr. Mohammed Abdellah General Pathology-2 sinaiuniversity. net • DISORDERS OF IMMUNE REACTION By the end of lecture you should be able to understand: . -DISORDERS OF IMMUNE REACTION. Definitions Antigen: a foreign protein that can evoke an immune response mediated by B (plasma cells) or T lymphocytes. When a tissue is antigenic = auto-antigen and leads to an autoimmune disease. Hapten: (incomplete antigen) a non-protein foreign substance (e.g. drug) that can evoke an immune response by combining with one of the body proteins (this combination acts as an antigen) . Antibodies: proteins secreted by plasma cells called immunoglobulins e.g. IgA, IgG, IgM ,IgE & IgD. -Secretions of T lymphocytes are called lymphokines. IMMUNITY: body defense mechanisms aiming at disposal of living irritants. Nonspecific immunity : including phagocytosis (macrophages and neutrophils), natural killer cells (nonspecific cytotoxic cells), opsonins (antibodies that help phagocytosis) and lysozyme (in saliva and other body secretions). Specific (acquired) immunity 1-Humoral immunity: Serum antibodies (immunoglobulins IgG , IgM, IgA, IgD & IgE) are secreted by plasma cells. Plasma cells develop from stimulated B lymphocytes. Examples of useful antibodies include bacteriolysins, agglutinins & others . 2-Cell- mediated immunity: Lymphokines (cellular antibodies) are secreted by stimulated T lymphocytes. These lymphokines have several functions e.g. specific activation of macrophages to engulf an organism. IMMUNOPATHOLOGY I- Hypersensitivity or allergy II- Autoimmunity III- Immunodeficiency IMMUNOPATHOLOGY I- Hypersensitivity or allergy -This is Exaggerated immune response. -It represents a harmful reaction against living irritants (bacteria, virus. etc) or non living irritants (such as food proteins, dust, pollens, drugs…etc) leading to tissue destruction. -There are 4 main types -Type I, II & III are mediated by immunoglobulins and develop rapidly (immediate hypersensitivity), -Type IV is mediated by sensitized T cells (cellmediated) and the reaction develops in a longer time, up to several days (delayed hypersensitivity). TYPE I HYPERSENSITIVITY (Immediate Hypersensitivity) Mechanism: Introduction antigen for the first time stimulates IgE formation, which becomes fixed to surface of mast cells. Re-exposure to same antigen produces reaction with IgE fixed on mast cell leading to liberation of histamine and other chemical mediators leading to: #Tissue necrosis. #Vasodilatation (which in systemic reactions leads to hypotension) #Allergic inflammation characterized by excess fluid exudate (oedema) and eosinophils #Bronchospasm #Increased mucus secretion by mucous glands TYPE I HYPERSENSITIVITY Examples: 1-Anaphylactic Shock: May follow rupture of hydatid cyst, injection of penicillin or antitoxic sera.... Manifestations develop within minutes and include: #Urticaria #Bronchospasm #Generalized oedema #Hypotension, shock and sometimes death. 2-Atopy (Atopic Diseases): Atopy means strange. This type of hypersensitivity has genetic predisposition. It differs from anaphylaxis in that IgE production is localized within a certain tissue or organ in contrast to the systemic production of IgE in case of anaphylaxis. Examples : #bronchial asthma, allergic rhinitis & allergic conjunctivitis. Thanks