1. Immune System Disorders Occasionally the reactions of the immune system are harmful: Instead of producing a desirable result, such as immunity to disease, the immune system may over-react, react to the wrong substances, or not react when it should. Instead of producing a desirable result, such as immunity to disease, the immune system may over-react, react to the wrong substances, or not react when it should. The immune system may fail to detect an infectious agent that has penetrated the first and second lines of defense. Some immune system disorders cause only discomfort, as in the case of hayfever. Immune system failure may lead to life- threatening conditions, such as anaphylaxis, AIDS and cancer (when the abnormal tumor cells escape immune system detection). Kaposi’s sarcoma in the foot area of an immune supressed AIDS patient Photo: CDC

2. Autoimmune Diseases Some people have an immune system that fails to appropriately recognize substances from their own body and attacks them. Some people have an immune system that fails to appropriately recognize substances from their own body and attacks them. Autoimmune diseases are the result of the damage caused by the immune system responding to self antigens. Rheumatoid arthritis Inflammation of joints leading to destruction of cartilage. Hemolytic anemia A disorder in which the red blood cells rupture or are destroyed at an excessive rate. Caused by a variety of factors including excessively fragile red blood cells, hereditary, and autoimmune disorders. Multiple sclerosis A progressive inflammatory disease causing paralysis. Caused by the myelin layers around nerve axons being destroyed. Axon Myelin layer

3. Hypersensitivity Hypersensitivity refers to an immune system response to an antigen beyond what is considered normal. The immunological response to the antigen (or allergen) leads to tissue damage rather than immunity. Hypersensitivity reactions occur when a person has been sensitized to an antigen. Allergic reactions (e.g. hayfever, asthma, and anaphylaxis from insect venom or drug injections) are rapid. They occur when antibodies respond to an allergen by causing the release of histamine from mast cells. An SEM photo showing a pollen grain Photo: EII Photo: Eyewire

5. Allergies When the immune system responds to harmless substances When the immune system responds to harmless substances Allergens – antigenic substances which do no real harm Allergens – antigenic substances which do no real harm Allergens include house dust, animal skin, pollen, house dust mite and its faeces Allergens include house dust, animal skin, pollen, house dust mite and its faeces

6. Allergies Histamine causes blood vessels to widen and become leaky. Histamine causes blood vessels to widen and become leaky. Fluid and white blood cells leave capillaries. Fluid and white blood cells leave capillaries. The area of leakage becomes hot, red and inflamed The area of leakage becomes hot, red and inflamed

7. Allergies Allergic responses such as asthma are the result of a vigorous overreaction of the immune system to a previously encountered antigen. Allergic responses such as asthma are the result of a vigorous overreaction of the immune system to a previously encountered antigen. Mast cells are immune cells involved in allergic responses, they are non- motile, found around blood vessels, in connective tissue and in the lungs. Mast cells release active agents such as Histamine, which cause contraction of smooth muscles & vasodilation of blood vessels, leading to swelling and inflammation. Treatment includes use of antihistamine drugs. Mast cells are immune cells involved in allergic responses, they are non- motile, found around blood vessels, in connective tissue and in the lungs. Mast cells release active agents such as Histamine, which cause contraction of smooth muscles & vasodilation of blood vessels, leading to swelling and inflammation. Treatment includes use of antihistamine drugs.

8. The mast cell binds the allergen when it encounters it again. The mast cell releases histamine and other chemicals, which together cause the symptoms of an allergic reaction. Vesicles with histamine Antibodies bind to specific receptors on the surface of the mast cells. Mast cell The Basis of Hypersensitivity The plasma cell produces antibodies. Plasma cell B cell encounters the allergen and differentiates into numerous plasma cells. B cell

9. Hayfever Hayfever (allergic rhinitis) is an allergic reaction to airborne substances such as: dust, moulds, pollens, and animal fur or feathers. Allergy to wind-borne pollen is the most common. Certain plants (e.g. ragweed and privet) are highly allergenic. There appears to be a genetic susceptibility to hayfever, as it is common in people with a family history of eczema, hives, and/or asthma. Those with hayfever are best to avoid the allergen, although anti-histamines, decongestants, and steroid nasal sprays will assist in alleviating symptoms. A privet plant in flower Photo: James H. Miller, USDA Forest Service, Forestryimages.org An SEM photo showing a pollen grain Photo: EII

11. Asthma Attacks can occur at any time Attacks can occur at any time Genes play a role in who develops asthma Genes play a role in who develops asthma Breathing becomes difficult, sufferers experience wheezing, coughing, a tightness about the chest and shortage of breath. Breathing becomes difficult, sufferers experience wheezing, coughing, a tightness about the chest and shortage of breath. 1/7 children in UK has asthma, number is increasing. 1/7 children in UK has asthma, number is increasing. >1000 people die each year from asthma every year in the UK >1000 people die each year from asthma every year in the UK

12. Asthma Airways in asthmatics are always inflamed, during an attack this worsens. Airways in asthmatics are always inflamed, during an attack this worsens. Fluid leaks from blood into airways and goblet cells secrete lots of mucus Fluid leaks from blood into airways and goblet cells secrete lots of mucus Airways can become blocked Airways can become blocked Muscles surrounding trachea and bronchioles contract which narrows airways further Muscles surrounding trachea and bronchioles contract which narrows airways further

13. Asthma Vaccines are being developed to make allergic responses less severe Vaccines are being developed to make allergic responses less severe Designed to desensitise people so they do not produce antibodies to allergens Designed to desensitise people so they do not produce antibodies to allergens Genetic tests may be used to screen children and then a vaccine could be given to prevent them developing asthma Genetic tests may be used to screen children and then a vaccine could be given to prevent them developing asthma

14. Blood groupAntigens present on the red blood cellsAntibodies present in the plasma A Contains anti-B antibodies, but no antibodies that would attack its own antigen A B Contains anti-A antibodies, but no antibodies that would attack its own antigen B AB Contains neither anti-A or anti-B antibodies O Contains both anti-A and anti-B antibodies antigen A antigen B antigens A and B Neither antigen A nor B