Diagnostic Tests in Biology

ELISA Tests

• ELISA (enzyme-linked immunosorbent assay) tests are used to detect hormones.
• Pregnancy tests and at-home COVID tests are simplified examples of ELISA tests.

Western Blot Test

• A highly accurate technique to detect specific antigens in complex mixtures.
• Separates antigens by size, reducing misinterpretation.
• An example is the HIV ELISA test.

Nucleic Acid Tests (NAT)

• Detect pathogen genetic material using molecular techniques.
• Southern blot detects specific DNA sequences.
• Northern blot detects specific RNA sequences.
• Used to detect infection even without symptoms.
• Also used to detect cancer.
• Probes bind to target molecules to identify specific sequences.

Polymerase Chain Reaction (PCR)

• Reverse transcription PCR (RT-PCR) amplifies specific RNA from small samples.
• Copies the target molecule exponentially (doubling every cycle): 4, 8, 16, 32 copies.
• Detection of a positive result in PCR indicates active replication.

Immunologic Disorders

Type 1 Hypersensitivity

• Allergic reactions triggered by allergens.
• Common examples: pollen, cats, bee stings, foods, drugs, ragweed, and dust mites.
• Exposure releases inflammatory molecules (histamine, kinins, proteases, leukotrienes).
• IgE-mediated two-step process:
  • Sensitization: Initial exposure activates B cells, producing IgE antibodies targeting the allergen. IgE binds to mast cells, basophils, or eosinophils.
  • Degranulation: Allergen binding causes mast cells, basophils, or eosinophils to release histamine and other cytokines.
• Symptoms: Skin redness, swelling, watery eyes, and potentially asthma (inhaled allergens).
• Systemic Anaphylaxis (anaphylactic shock): From localized to systemic, causing low blood pressure, airway constriction, and rapid death.
• Treatment: Immediate epinephrine, avoidance of the allergen.

Type 2 Hypersensitivity

• Antibody-mediated destruction of cells.
• Complement and antibodies work together.
• Examples: Incompatible blood transfusions, hemolytic disease of the newborn, drug reactions (e.g., penicillin).

Type 3 Hypersensitivity

• Immune complexes form, some cleared, others lodge in blood vessels or organs.
• Leads to inflammation and tissue damage.
• Localized reactions: Inhalation of antigens can lead to immune complex formation and complement activation (e.g., farmer's lung, pigeon breeders' lung).
• Systemic reactions: Rheumatoid arthritis and systemic lupus erythematosus.

Type 4 Hypersensitivity

• Cellular hypersensitivity: Inflammation 12-24 hours after exposure to antigen triggered by antigen-presenting cells, and T-cells response.
• Types:
  • Contact dermatitis: Poison ivy, latex, soaps.
  • Tissue/organ rejection: Post-transplantation.
  • Cell-mediated immune response (T Cells): Intense skin rash, treatable with glucocorticoids.
• Tuberculin Response: Diagnoses tuberculosis or vaccination exposure; skin reaction (swelling) 24-72 hours post-exposure aids diagnosis. Larger reaction indicates excessive immune response.

Graft Rejection

• Recipient's immune system recognizes transplanted tissue/organ as foreign due to MHC or HLA differences.
• Immunosuppressive drugs help prevent graft-versus-host disease.

Development of Autoimmune Diseases

• Loss of self-recognition (clonal deletion) leads to autoantibodies or cytotoxic T cells attacking normal body components.
• More common in older women due to hormone differences and potentially immune exhaustion.
• Genetic and environmental factors contribute to autoimmune diseases.
• Examples include type 1 diabetes mellitus, multiple sclerosis, rheumatoid arthritis, and autoimmune hemolytic anemia.

Primary Immunodeficiencies

• Agammaglobulinemia: B cell deficiency, treated with immune serum and antibiotics.
• DiGeorge syndrome: Thymus gland defect, T cell deficiency, treated with thymic stem cells.

Acquired Immunodeficiencies

• Infections (leprosy, tuberculosis, AIDS), immunosuppressants (chemotherapy/radiation therapy) damage T/B cells.

HIV/AIDS

• Infection by human immunodeficiency virus (HIV).
• Targets T helper cells and macrophages.
• Results in opportunistic infections/cancers and death.
• Transmission: Sexual contact, blood products, mother-to-child transmission.

Bacterial Skin Diseases

• Folliculitis: Hair follicle infection.
• Staphylococcal Scalded Skin Syndrome: Caused by S. aureus.
• MRSA Infections: Methicillin-resistant Staphylococcus aureus.
• Necrotizing Fasciitis: Severe tissue infection.
• Cat Scratch Fever: Bacterial infection.
• Acne: Inflammation of sebaceous glands.
• Pseudomonas Infections.
• Gas Gangrene

Staphylococcus aureus (S. aureus) Diseases

• Common causes of various skin infections, bacteremia, food poisoning, and pneumonia
• Gram-positive, facultatively anaerobic.
• Can survive in salty and dry conditions (tolerates various environments)
• Treatment: Methicillin; prevention: antisepsis.
• Spread: Direct contact with infected individuals or surfaces (fomites).

This quiz covers various diagnostic tests used in biology, including ELISA, Western Blot, Nucleic Acid Tests, and PCR. Explore the principles and applications of these techniques, which are crucial in detecting hormones, pathogens, and genetic material. Test your knowledge on how these assays function and their significance in medical diagnostics.