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Hypersensitivity (Type 1 - Immediate (anaphlactic) (Clinical aspects…

- - - - antigen re-exposure binds to IgE and triggers granules release from mast cells and basophils (degranulation of mast cells)
        
        Ways which mast cells can degranulate
        
        Lectin cross linking (lectin binds to two IgE)
        
        Chemical cross linking (chemical binds to two IgE)
        
        Anti IgE cross linking (anti IgE binds to two IgE)
        
        Anti Fc-epsilon receptor high affinity (FcεRI) cross linking (anti FcεRI binds to FcεRI)
        
        Granules releases preformed mediators and newly synthesized mediators
        
        Thromboxane, cytokines, eosinophil chemotactic factor
        
        esosinophil chemotaxis activation, degranulation
        
        tissue damage
        
        Neutrophil chemotactic factor
        
        neutrophil chemotaxis activation, phagocytosis, degranulation
        
        tissue damage
        
        Cytokines
        
        infiltration of B lymphocytes, T lymphocytes and macrophages
        
        antibody production, macrophage phagocytosis
      - Requirement: at least 2 Fc receptors are joined together in stable configuration
    - - Results of granules binding to target cells in the host
      - 2 effector cells : mast cells and basophils
        
        Mast cells - in tissue
        
        Basophils - in circulation
      - Both possess Fc receptor for IgE
    - - First encounter with antigen results in IgE production (T-cell dependent)
      - IgE binds mast cells and basophils
  - - - leads to detrimental effects
  - - - Injection of increasing antigen dosage
        over extended period
    - - Usage of drugs such as cromolyn solution,
        antihistamines, epinephrine
    - - avoid potential allergens area
- - - - Graft vs host reaction
      - Contact sensitivity (Dermatitis)
        
        target cells - in skin
        
        eg. Metal like nickel chromate
        
        metal coupled with to free amino group of skin protein to form neoantigen (non-self antigen)
        
        Neoantigen processed in Langerhans cells and sensitized T helper 1 cells
        
        re-exposure to metal cause inflammatory reaction at the site of contact
        
        Characteristics - skin is rough and scaly (Eczema)
        
        Caused by Poison Ivy
        
        Pentadeca catechol molecules binds to skin proteins
        
        Primary contact - 7-10 days (no dermatitis)
        
        Secondary contact - 1-2 days (dermatitis)
        
        Caused by wearing latex gloves
  - - - In some cases, the edge of granuloma is walled off by epitheloid cells and fibrin, leading to further necrosis due to lack of oxygen
      - Lytic agents and enzymes released by the macrophage-derived cells within the granuloma causes tissue damage and necrosis
      - Mixture of Th cells, macrophages, epitheloid cells and giant multinucleated cells form granuloma
      - Stimulated macrophages will differentiate into epitheloid cells which can fuse to form giant multinucleated cells
      - if the macrophage cant engulf the pathogen, Th cell will continue stimulating and at the same time will stimulate macrophages
  - - - the protein is injected subcutaneously
      - induration forms within 48 hours
- - - - Rh- mother carrying her first Rh+ fetus. Rh antigens from the developing fetus can enter the mother's blood during delivery
      - In response to the fetal Rh antigens, the mother will produce anti-Rh antibodies
      - Rh+ from father
      - If the woman becomes pregnant with another Rh+ fetus, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells
    - - binding of drugs or metabolites to red blood cell or platelets
        
        Sedormid binds platelets - thrombocytopenia
        
        Penicillin binds RBC - anaemia
      - Mechanisms
        
        Antibody binds to the complex on plasma membrane
        
        Complement is activated
        
        Drug-plasma protein complex bind to membrane of red blood cell
        
        Cell is lysed
        
        Drug binds to plasma protein forming drug-plasma protein complex
    - - ABO blood groups variants due to differences in glycosylation of red blood cell glycoprotein
      - If incompatible blood is given in a transfusion, the donor cells are treated as if they were foreign invaders, and the patient's immune system attacks them accordingly. Not only is the blood transfusion rendered useless, but a potentially massive activation of the immune system and clotting system can cause shock, kidney failure, circulatory collapse, and death.