topic 3.2

Question 1

what are hypersensitivity or allergic reactions?

Answer 1

excessive or unusual immune reactions that cause tissue damage

Question 2

what does sensitised mean?

Answer 2

the development of an immune response subsequent to exposure to an antigen

Question 3

what is hypersensitivity?

Answer 3

when the immune system produces an excessive and damaging immune response to a harmless antigen

Question 4

what three types of antigens does hypersensitivity usually occur to?

Answer 4

1. harmless antigens from the environment (allergens)
2. antigens from microbes
3. antigens from own self (self-antigens)

Question 5

what are the 4 types of hypersensitivity?

Answer 5

1. allergic reaction
2. cytotoxic hypersensitivity
3. immune complex hypersensitivity
4. cell-mediated/delayed hypersensitivity

Question 6

explain type 1 hypersensitivity (allergic reaction)

Answer 6

• caused by production of IgE antibodies from B cells which bind to mast cells
• re-exposure to antigen causes it to attach to IgE sensitised mast cell = release of chemical mediators which = rapid inflammatory response

Question 7

explain immune complex hypersensitivity?

Answer 7

• antigen + antibody = complex deposited into tissue, causing local inflammatory response
• soluble agents bind to antibodies, forming immune complex
• immune complexes lodges into blood vessels, joints + glomeruli, causing inflammatory process to start

Question 8

explain cytotoxic hypersensitivity?

Answer 8

• antigen present on cell membrane, may be normal or foreign
• circulating IgG antibodies bind to antigens on patient’s cell surfaces
• these cells recognised by macrophages, then act as antigen-presenting cells, causing B cell response + antibody production against antigen
• cell then destroyed

Question 9

explain cell-mediated/delayed hypersensitivity?

Answer 9

• delayed response by sensitised T cells to specific antigen = cytokine release + inflammatory response + destruction of antigen
• helper T cells recognise antigen on surface of APC
• CD4+ T cells secrete IL-2 + interferon = immune response
• activated T cytotoxic cells destroy target cells on contact

Question 10

what is anaphylaxis?

Answer 10

a serious, life-threatening, systemic type 1 hypersensitivity reaction

Question 11

explain the pathophysiology of anaphylaxis

Answer 11

• chemical mediators (histamines) released rapidly from mast cells within connective tissue, into general circulation
• general and/or systemic vasodilation occurs = sudden, severe onset of hypotension (low BP)
• in lungs, oedema of mucosa + bronchoconstriction = serious respiratory dysfunction

Question 12

what is recommended treatment for anaphylaxis?

Answer 12

1. noradrenaline (epinephrine) injection immediately
2. antihistamine useful in early stages

Question 13

briefly explain autoimmune disorders

Answer 13

these occur when excessive and inappropriate inflammatory reaction occurs against self-antigens

Question 14

explain the mechanism of autoimmune disorders

Answer 14

• occur when individuals develop antibodies against own cells/cellular material
• self-tolerance to own antigens lost, thus immune system cannot discern self from non-self, auto-antibodies then trigger immune response, leading to inflammation + possible necrosis

Question 15

what are immunomodulating agents?

Answer 15

agents that modify the body’s immune responsiveness

Question 16

what are the two categories of immunomodulating agents?

Answer 16

1. immunostimulants - increase immune responsiveness to fight cancer or infection
2. immunosuppressants - suppress immune reactions associated with hypersensitivity reactions + autoimmune disease

Question 17

true or false: immunosuppressant agents can be used to prevent rejection of transplanted tissues/organs, autoimmune diseases and hypersensitivity reactions?

Answer 17

true

Question 18

what effect do corticosteroids have on the immune system?

Answer 18

• reduce size and contents of lymph nodes and spleen
• suppress T cell activity
• suppress macrophage activity

Question 19

explain cyclosporin?

Answer 19

• cyclosporin belongs to group of immunosuppressants called calcineurin inhibitors
• it is actually an antibiotic but has immunpsuppressing actions

Question 20

what is the mechanism of action of calcineurin inhibitors?

Answer 20

prevent proliferation of T cells after antigen presentation, done without affecting phagocytosis, sensitised T cell function or suppressing bone marrow cells

Question 21

what are monoclonal antibodies?

Answer 21

those made by a single B cell clone, which makes each antibody identical and highly specific for one antigen

Question 22

what does the suffix ‘_mab’ indicate?

Answer 22

that it is a monoclonal antibody