interteach #1 hypersensitivity, molecular mimicry, strep throat, CBC

What is a hypersensitivity reaction?

An immune-mediated response that causes tissue injury and disease rather than protection due to excessive or misdirected immune activity

What do all hypersensitivity reactions have in common?

They are immune-mediated, inflammatory, require prior sensitization, and can cause tissue damage

How are hypersensitivity reactions classified?

They are classified into four types based on the immune mechanism causing tissue damage

What is Type I hypersensitivity?

An immediate hypersensitivity reaction mediated by immunoglobulin E involving mast cell degranulation and histamine release

What triggers Type I hypersensitivity?

Re-exposure to an allergen that cross-links immunoglobulin E on mast cells

What is the mechanism of Type I hypersensitivity?

Allergen exposure leads to immunoglobulin E production, binding to mast cells, and histamine release upon re-exposure

What is the timing of Type I hypersensitivity?

Occurs within seconds to minutes after exposure

What is the main mediator of Type I hypersensitivity?

Histamine

What are examples of Type I hypersensitivity?

Anaphylaxis, asthma, allergic rhinitis, and food allergies

What is Type II hypersensitivity?

An antibody-mediated hypersensitivity reaction in which immunoglobulin G or immunoglobulin M targets cell surface antigens

What is the mechanism of Type II hypersensitivity?

Antibodies bind to cell surface antigens, activate complement, and lead to cell destruction

What does Type II hypersensitivity target?

Specific cells or tissues of the body

What are examples of Type II hypersensitivity?

Autoimmune hemolytic anemia, Goodpasture syndrome, and rheumatic fever

What is Type III hypersensitivity?

A hypersensitivity reaction caused by deposition of antigen–antibody immune complexes in tissues

What is the mechanism of Type III hypersensitivity?

Immune complexes deposit in tissues, activate complement, and cause inflammation and organ damage

Which organs are commonly affected in Type III hypersensitivity?

Blood vessels, kidneys, and joints

What are examples of Type III hypersensitivity?

Systemic lupus erythematosus, serum sickness, and post-streptococcal glomerulonephritis

What is Type IV hypersensitivity?

A delayed hypersensitivity reaction mediated by T lymphocytes rather than antibodies

What is the mechanism of Type IV hypersensitivity?

Sensitized T cells release cytokines that recruit macrophages and cause tissue damage

What is the timing of Type IV hypersensitivity?

Occurs 48 to 72 hours after exposure

What are examples of Type IV hypersensitivity?

Contact dermatitis and the tuberculosis skin test reaction

What is molecular mimicry?

An autoimmune mechanism in which microbial antigens structurally resemble host antigens, leading to cross-reactive immune responses

What causes molecular mimicry?

Structural similarity between pathogen antigens and host self-antigens

Why does molecular mimicry cause tissue damage?

Antibodies or T cells generated against pathogens cross-react with self tissues and trigger inflammation

Which immune components are involved in molecular mimicry?

Antibodies in Type II or Type III reactions and T cells in Type IV reactions

What diseases are associated with molecular mimicry?

Rheumatic fever, Guillain-Barré syndrome, multiple sclerosis, and type 1 diabetes

What organism causes strep throat?

Streptococcus pyogenes, a Group A beta-hemolytic streptococcus

How does Streptococcus pyogenes cause disease?

It adheres to pharyngeal epithelium using M protein and produces toxins that trigger inflammation

What are the classic symptoms of strep throat?

Sore throat, fever, tonsillar exudates, and anterior cervical lymphadenopathy

What is the first-line treatment for strep throat?

Penicillin or amoxicillin administered for ten days

Why is treatment of strep throat important?

It prevents immune-mediated complications such as acute rheumatic fever

What is acute rheumatic fever?

An autoimmune inflammatory disease that develops weeks after untreated streptococcal infection

What immune mechanism causes acute rheumatic fever?

Molecular mimicry involving antibodies against streptococcal antigens

What organs are affected in acute rheumatic fever?

The heart, joints, skin, and central nervous system

What autoantibodies are associated with rheumatic fever?

Anti-streptolysin O and anti-DNase B antibodies

What are the major Jones criteria?

Carditis, migratory polyarthritis, chorea, erythema marginatum, and subcutaneous nodules