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The immune system evolved for what purpose?
To isolate/eliminate pathogens
What 2 problems can occur with the immune system?
What is hypersensitivity?
An immune response to an environmental agent (allergen)
Hypersensitivity = ?
What are the 4 types of hypersensitivity?
Type I: immediate or anaphylactic
Type II: antibody-dependent cytotoxic
Type III: immune-complex
Type IV: delayed or cell-mediated
What is Type I hypersensitivity?
Immediate-type or anaphylactic hypersensitivity
Fast! Occurs 5-30 minutes after exposure
Give examples of Type I hypersensitivity.
Immediate-type or anaphylactic hypersensitivity:
inhaled: hay fever, pet dander, mold spores, dust mites
injected: bee sting allergies, vaccines, drugs
ingested: food, orally administered drugs (penicillin)
Describe the step-by-step process of Type I hypersensitivity.
1. initial allergen exposure induces IgE production
2. IgE "sensitizes" mast cell by attaching its FC region (leg of Ab) to mast cell surface receptor (IgE normally is not on mast cells.
3. subsequent allergen exposure
4. Fc receptors cross linked
5. degranulaltion of histamine and/or leukotriens (highly inflammatory)
What is Type II hypersensitivity?
Antibody-dependent cytotoxic hypersensitivity
Ab combines with host cell--death by complement activation or phagocytosis
Give examples of Type II hypersensitivity.
Antibody-dependent cytotoxic hypersensitivity:
blood group incompatibility
Rh factors in pregnancy
AB - universal recipient
O - universal donor
Rh+ can accept + or -
Rh- can only accept -
Ab can cross placenta
What is Type III hypersensitivity?
Small particulate Ab-Ag combination (called immune complex)
This complex can stimulate the rest of the immune system
-results in surrounding host cell/tissue destruction
What is Type IV hypersensitivity?
Delayed or Cell-mediated hypersensitivity:
Occurs ~24-72 hours after Ag exposure
-TB skin test
What is Autoimmunity?
An immune response to self proteins
Immune cells that attack the host (self) are removed during fetal development
Autoimmunity is loss of self tolerance
Types of Autoimmune Diseases:
Cytotoxic autoimmune reactions
Immune complex autoimmune reactions
Cell-mediated autoimmune reactions
An Autoimmune disease--Cytotoxic autoimmune reactions
Antibodies react to cell-surface Ag
No cytotoxic destruction of host cells
(muscle weakness)--make Ab against Ach receptors and the receptors get destroyed
An Autoimmune disease--Immune complex autoimmune reactions
Immune complexes are deposited on host cells
Systemic lupus erythematosus
--autoimmune response is directed at autoantigens present in almost all host cells. Inflammatory reaction = cell/tissue destruction. Trigger factors remain unknown
--joint infiltration with immune cells. Eventually, immune cells release proteinases and collagenases that damage cartilage, ligaments, and tendons.
An Autoimmune disease--Cell-mediated autoimmune reactions
Mediated by T cells (no antibodies)
--immune response to myelin basic protein. Infiltration of immune cells in CNS. Create T cells that attack myelin sheath.
Insulin-dependent diabetes mellitus
--selective destruction of insulin producing cells in the pancreas. AKA type I diabetes (juvenile-onset). Attacks insulin-making cells--> B cells.