PATHOPHYSIOLOGY STUDY GUIDE
Hypersensitivity • Autoimmunity •
Immunodeficiency
Easy Memory Tricks + Simplified Notes
1. HYPERSENSITIVITY REACTIONS
Hypersensitivity = OVERREACTIVE immune response. The immune system attacks too hard and causes
tissue damage.
MEMORY TRICK: Think ACID → A = Allergic (Type 1), C = Cytotoxic (Type 2), I = Immune
complex (Type 3), D = Delayed (Type 4)
TYPE 1 – ALLERGIC / ANAPHYLACTIC
Main mechanism: IgE + mast cells + histamine
Key idea: Fast reaction
Examples: Anaphylaxis, asthma, allergic rhinitis
TYPE 2 – CYTOTOXIC
Main mechanism: IgG or IgM attack cells
Key idea: Cell destruction
Examples: Graves disease, hemolytic anemia
TYPE 3 – IMMUNE COMPLEX
Main mechanism: Antigen + antibody complexes deposit in tissue
Key idea: Inflammation + tissue damage
Examples: SLE
TYPE 4 – DELAYED
Main mechanism: T-cell mediated
Key idea: Delayed 24–72 hr reaction
Examples: Poison ivy, latex rash
2. TYPE 1 HYPERSENSITIVITY
Mediated by IgE antibodies
Mast cells release HISTAMINE
Causes vasodilation, bronchoconstriction, mucus
, Symptoms: urticaria, wheezing, itching, hypotension
MEMORY TRICK: TYPE 1 = FAST allergy reaction
Anaphylaxis
Life-threatening emergency
Airway swelling + hypotension
Treatment = IM EPINEPHRINE FIRST
Support airway, oxygen, IV fluids
MEMORY TRICK: If airway closes → epinephrine NOW
Allergic Rhinitis
Hay fever caused by allergens
Sneezing, itchy eyes, runny nose
Triggers: pollen, dust mites, pet dander
3. TYPE 2 HYPERSENSITIVITY
IgG or IgM attack body cells
Complement activated → cell destruction
Macrophages phagocytize damaged cells
MEMORY TRICK: TYPE 2 attacks CELLS directly
Graves Disease
Autoantibodies stimulate TSH receptor
Too much thyroid hormone = hyperthyroidism
Signs: bulging eyes, goiter, weight loss, tachycardia, heat intolerance
Diagnosis: TSH low, T3/T4 high
Treatment: antithyroid meds, radioactive iodine, thyroidectomy
MEMORY TRICK: Graves = FAST metabolism
4. TYPE 3 HYPERSENSITIVITY
Immune complexes deposit in tissues
Complement activation causes inflammation
Neutrophils release enzymes → tissue damage
MEMORY TRICK: TYPE 3 = immune complexes STUCK in tissues
SLE – Systemic Lupus Erythematosus
Hypersensitivity • Autoimmunity •
Immunodeficiency
Easy Memory Tricks + Simplified Notes
1. HYPERSENSITIVITY REACTIONS
Hypersensitivity = OVERREACTIVE immune response. The immune system attacks too hard and causes
tissue damage.
MEMORY TRICK: Think ACID → A = Allergic (Type 1), C = Cytotoxic (Type 2), I = Immune
complex (Type 3), D = Delayed (Type 4)
TYPE 1 – ALLERGIC / ANAPHYLACTIC
Main mechanism: IgE + mast cells + histamine
Key idea: Fast reaction
Examples: Anaphylaxis, asthma, allergic rhinitis
TYPE 2 – CYTOTOXIC
Main mechanism: IgG or IgM attack cells
Key idea: Cell destruction
Examples: Graves disease, hemolytic anemia
TYPE 3 – IMMUNE COMPLEX
Main mechanism: Antigen + antibody complexes deposit in tissue
Key idea: Inflammation + tissue damage
Examples: SLE
TYPE 4 – DELAYED
Main mechanism: T-cell mediated
Key idea: Delayed 24–72 hr reaction
Examples: Poison ivy, latex rash
2. TYPE 1 HYPERSENSITIVITY
Mediated by IgE antibodies
Mast cells release HISTAMINE
Causes vasodilation, bronchoconstriction, mucus
, Symptoms: urticaria, wheezing, itching, hypotension
MEMORY TRICK: TYPE 1 = FAST allergy reaction
Anaphylaxis
Life-threatening emergency
Airway swelling + hypotension
Treatment = IM EPINEPHRINE FIRST
Support airway, oxygen, IV fluids
MEMORY TRICK: If airway closes → epinephrine NOW
Allergic Rhinitis
Hay fever caused by allergens
Sneezing, itchy eyes, runny nose
Triggers: pollen, dust mites, pet dander
3. TYPE 2 HYPERSENSITIVITY
IgG or IgM attack body cells
Complement activated → cell destruction
Macrophages phagocytize damaged cells
MEMORY TRICK: TYPE 2 attacks CELLS directly
Graves Disease
Autoantibodies stimulate TSH receptor
Too much thyroid hormone = hyperthyroidism
Signs: bulging eyes, goiter, weight loss, tachycardia, heat intolerance
Diagnosis: TSH low, T3/T4 high
Treatment: antithyroid meds, radioactive iodine, thyroidectomy
MEMORY TRICK: Graves = FAST metabolism
4. TYPE 3 HYPERSENSITIVITY
Immune complexes deposit in tissues
Complement activation causes inflammation
Neutrophils release enzymes → tissue damage
MEMORY TRICK: TYPE 3 = immune complexes STUCK in tissues
SLE – Systemic Lupus Erythematosus
