Immune System Disorders and Hypersensitivity

Immune System Disorders

• Primary Immunodeficiencies: Congenital disorders caused by genetic mutations, affecting both B and T cells. Severe combined immunodeficiency (SCID) is an example.
• Secondary Immunodeficiencies: Acquired disorders caused by external factors like HIV infection (AIDS). HIV destroys CD4+ T cells, weakening the immune system for opportunistic infections.

Hypersensitivity Reactions

• Type I (Anaphylactic): Immediate hypersensitivity—allergies, bee stings. IgE antibodies trigger mast cell histamine release, causing symptoms like swelling, itching, and difficulty breathing.
• Type II (Cytotoxic): Antibody-mediated cell destruction. Example: Hemolytic disease of the newborn, where maternal antibodies target fetal red blood cells.
• Type III (Immune Complex): Antigen-antibody complexes deposit in tissues—inflammation and damage occur—e.g., rheumatoid arthritis.
• Type IV (Delayed): T cell-mediated; delayed-type hypersensitivity. Example: Poison ivy reaction.

Autoimmune Disorders

• Cause: Immune system mistakenly attacks self-antigens—e.g., Type 1 diabetes (immune system attacks insulin-producing beta cells).

Transplant Reactions

• Types of Grafts:
  • Autograft: Self to self
  • Isograft: Identical twins
  • Allograft: Between humans
  • Xenograft: Between species
• Rejection: Mismatched major histocompatibility complex (MHC) or human leukocyte antigen (HLA) molecules trigger immune response. Tissue typing helps to minimize this.

Immune Surveillance

• Process: Immune system monitors and eliminates abnormal, cancerous cells. Natural killer (NK) cells destroy early-stage tumors

Immunology and Diagnostic Tests

• Vaccines:

  • Live attenuated: Weakened pathogens—MMR vaccine; strong response, risk of reversion.
  • Inactivated: Killed pathogens—polio; safer, weaker response.
  • Subunit: Specific antigens—HPV vaccine; specific antigens.
  • Toxoid: Inactivated toxins—tetanus vaccine; toxin-based immunity.
  • mRNA: Teach cells to make antigen proteins—e.g., COVID-19 vaccines.
  • Conjugate: Combine weak antigens with strong proteins—e.g., Hib vaccine.

• Diagnostic Tests:

  • Precipitation: Detects soluble antigen-antibody complexes.
  • Agglutination: Clumping—blood typing.
  • Neutralization: Blocks toxins/viruses—rabies test.
  • Complement fixation: Detects antibodies in serum.
  • Fluorescent-antibody: Visualize antibody-antigen binding under UV light.
  • ELISA: Measure antigens/antibodies—e.g., HIV test.
  • PCR-based: Detect genetic material—quickly and accurately.

Microbial Control Methods

• Methods:

  • Sterilization: Kills all microbes—autoclaving.
  • Disinfection: Reduces microbes on surfaces.
  • Antisepsis: Reduces microbes on living tissue.
  • Degerming: Removes microbes mechanically—handwashing.
  • Sanitization: Reduces microbes to safe levels.

• Physical Methods:

  • Thermal death point/time (TDP/TDT): Lowest temp/time needed to kill.
  • Moist heat: Boiling, autoclaving
  • Dry heat: Incineration, hot air
  • Filtration: For heat-sensitive materials
  • Low temperatures: Refrigeration.

• Chemical Methods:

  • Ethylene oxide: Sterilizes heat-sensitive equipment.
  • Alcohol (70%): Denatures proteins
  • Other agents: Surfactants, heavy metals (e.g., silver nitrate), nitrites/nitrates.

Antimicrobial Drugs and Resistance

• Mechanisms of Action:

  • Antibacterial: Target cell walls, protein synthesis, nucleic acids or cell membranes.
  • Antifungal: Target ergosterol in fungal cell membranes
  • Antiviral: Block replication
  • Antihelminthic: Disrupt parasite metabolism

• Resistance: Efflux pumps, enzyme production (e.g., beta-lactamases), altered targets.

• Testing Effectiveness:

  • Disk diffusion (Kirby-Bauer): Measures zones of inhibition.
  • E-test: Determines the minimum inhibitory concentration (MIC).
  • MBC: Minimum bactericidal concentration.

This quiz covers key concepts related to immune system disorders, including primary and secondary immunodeficiencies. It also explores the four types of hypersensitivity reactions, illustrating how the immune system can react adversely. Test your knowledge on these critical aspects of immunology.