Hypersensitivity Disease 1

Question 1

define hypersensitivity reactions

Answer 1

immune response that results in bystander damage to the self
usually exaggeration of normal immune mechanisms
pathophysiological basis for many chronic diseases, including allergy and autoimmunity
(the basis of transplanted tissue rejection)

Question 2

explain classification of hypersensitivity reactions

Answer 2

type I - immediate hypersensitivity - allergy
type II - direct cell effects (cytotoxic or stimulatory - type V hypersensitivity reactions)
type III - immune complex mediated
type IV - delayed type hypersensitivity

Question 3

describe type I hypersensitivity - allergy

Answer 3

IgE mediated antibody response to external antigen (allergen), onset in seconds
characterised by greatly enhanced sensitivity to normally innocuous substances, leading to physiological responses and tissue damage, resulting in the signs and symptoms of allergic reactions 
wide variety of conditions (asthma, hayfever, eczema etc.)
very common (prevalence increasing, environmental cause)
infectious trigger - helminths and worms

Question 4

describe the hygiene hypothesis

Answer 4

cause of increasing prevalence of allergens
improved sanitation and decreased incidence of infectious disease has a result in the world that is too clean;
results in increased predisposition to allergic conditions during childhood

Question 5

describe risk factors for allergic disease

Answer 5

environmental factors 
Th1 differentiation stimuli - no allergies;
older siblings 
early daycare exposure
rural environment 
childhood infections 
microbial exposure
pets

lack of Th1 differentiation stimuli - Th2 allergies and asthma;
only child
widespread use of ABX
urban environment with allergen sensitisation - dust mites and cockroaches

Question 6

describe Th2 effector cells

Answer 6

dendritic cell 
CD4+ T cell
Th0 via IL-2
Th0 differentiates;
Th1 - macrophages (super killers)
Tfh - B cell stimulation and high affinity Ig secretion 
Th2 - B cell - IgE class switching causing killing of parasites and drives allergic responses
refer to PP

Question 7

describe sensitisation stage of allergic disease

Answer 7

normal adaptive immune response;
mast cells and eosinophils express receptors or the Fc region of IgE antibody on their surface (Fce receptors)
on first encounter with allergen, B cells IgE antibody
allergen is cleared
residual IgE antibodies bind to circulating mast cells via Fce receptors

Question 8

describe allergic stage of allergic disease

Answer 8

re-encounter of allergen
allergen binds to IgE-coated mast cells and disrupts cell membrane
immediate release of vasoactive mediators (histamine, tryptase)
also increased expression of inflammatory cytokines and leukotrienes
causes calor, tumor, rubor and dolor

Question 9

describe clinical features of allergic disease

Answer 9

muscle spasm;
bronchoconstriction
wheeze

mucosal inflammation;
mucosal oedema and increases secretions
sputum production

inflammatory cell infiltrate;
infiltration of lymphocytes and eosinophils into bronchioles
sputum yellow