Failures of the Immune Response PDF

FAILURES OF THE IMMUNE RESPONSE Chapter 4 MIC343 Syllabus Content Immunodeficiencies Autoimmune disease Allergic reactions (Hypersensitivities)  Immunodeficiencies Immunodeficiency Primary caused by immunodeficiency infection diseases  Im...

FAILURES OF THE IMMUNE RESPONSE Chapter 4 MIC343 Syllabus Content Immunodeficiencies Autoimmune disease Allergic reactions (Hypersensitivities)  Immunodeficiencies Immunodeficiency Primary caused by immunodeficiency infection diseases  Immunodeficiency caused by infection HIV stands for Human Immunodeficiency Virus. It is the virus that causes AIDS. Structure  Course of infection The pathology of HIV infection consists of three phases : 1) The acute phases 2) The asymptomatic phases 3) The symptomatic phases The acute phases Virus is produced in large quantities by infected lymphocytes This initial viremia is greatly reduced → actions of Tc cells, which kill infected targets The asymptomatic phases The symptomatic phases Begins 3-4 months after the initial infection End stage of infection, the infected individual develops Memory T cells and dormant macrophages that the clinical symptoms of AIDS. contain HIV provirus serve as reservoirs for the Th and Tc cells count drops infection. When Th counts drop below 200 per microliter, the HIV is latent and does not make any new virions. patients are said to have AIDS Population of CD4 T helper declines at a steady rate. Increased susceptibility to opportunistic infections Also known as clinical latency (last for years) Cancers such as Kaposi’s sarcoma and B-cell lymphoma also develop in some patients Pathogenesis Multiplication steps Virus particles then bud from the cell  HIV → AIDS HIV infection leads to a weakened immune system. This makes a person with HIV vulnerable to a group of illness, e.g., opportunistic infections, that would not as easily affect a healthy person. AIDS results when HIV infection progresses to an advanced stage, damaging the immune system to a point at which the body can no longer fight illness. AIDS is a syndrome because it is characterized by a group of illnesses. Drugs are available which can treat HIV and AIDS. These drugs are called antiretrovirals (ARVs). They prevent the virus from replicating and slow the progress of the disease, but there is still no cure for AIDS or vaccine to prevent HIV transmission. Symptoms Symptoms Symptoms Transmission Transmission  Primary immunodeficiency diseases Result from genetic abnormalities present in the affected individual at birth Characterized by an immune system that does not function properly Can be caused by mutations in immune response genes Inherited immunodeficiency diseases are caused by genetic defects and these diseases can affect both the development and function of T cells ad B cells. There can also be defects in phagocytic cells, complement, or cytokine receptors → will result in a lack of proper host defense.  Primary immunodeficiency diseases B-Cell Defects Defects in Ab production → can result in severe and repeated infection with bacteria Defects in the development of B cells or to defects in the activation of the humoral response T-Cell Defects Defects in T-cell function can result in severe combined immunodeficiency syndrome (SCID) There is no T-cell function and therefore no cellular adaptive immune response Common primary immunodeficiency syndromes Respiratory infections Defects in accessory cells Defects in complement cascade → can lead to an increase in the occurrence of infectious disease Defects in phagocytic cells can cause widespread bacterial infections  Autoimmune disease Cause of Mechanisms of autoimmunity autoimmunity  Autoimmune disease Causes of autoimmunity In autoimmune reactions, the immune system reacts against the host Many autoimmune diseases are the result of production of autoantibodies, but multiple parts of the immune response are usually involved Some people are genetically predisposed to autoimmune disease but there is also some disease can be influenced by environmental factors Drugs and toxins can also cause autoimmunity  Organ specific Systemic Type 1 insulin-dependent diabetes mellitus → Systemic lupus erytomatosus (SLE) → autoimmune response to insulin producing cells in anti-chromatin ab attack the skin, the pancreas kidneys and brain Hashimoto’s thyroiditis and Grave’s disease → attack thyroid gland Rheumatoid arthritis → attacks joints Multiple sclerosis → attacks nervous system  Autoimmune disease Mechanism of autoimmunity Allergic reactions (Hypersensitivity) Effector mechanisms Clinical effects of in allergic reactions allergic reactions  Allergic reactions An allergic reactions is a type of immune response This response is generated against allergens (antigens) such as peanuts, pollen, dust-mite feces and etc Allergies can cause discomfort and distress for the patient Not life threatening but can sometimes cause anaphylaxis, a condition that can be fatal There are 4 main types of hypersensitivity reaction : type I, type II, type III, type IV Tissue  Effector mechanisms in allergic reactions Most IgE is found on the surface of mast cells, basophils and activated eosinophils → bound there by high-affinity receptors Mast cells → residents of mucosal and epithelial tissues, located in blood vessel, where they guard against invading pathogens and continuously express the IgE receptor on their surface When a person facing an allergens, the allergens crosslinks with IgE molecule bound to a receptor on a mast cell This causes degranulation of the mast cells → then a variety of inflammatory mediators are released Some mediators cause : immediate increases in local blood flow, vessel permeability and enzyme production → tissue destruction  Effector mechanisms in allergic reactions Eosinophils → found mainly in the connective tissue lying immediately under the respiratory, digestive and genitourinary epithelial Cause tissue damage and enhance the allergic reactions  Clinical effects of allergic reactions The clinical effects of allergic reactions vary according to the site of mast-cell activation These clinical effects depend on three variables : 1. The amount of allergen-specific IgE present on the mast cells 2. The route by which the allergen is introduced into the body 3. How much allergens enters the body