Immune System Terminology and Functions

Immune System Terminology

• Antigen: A substance that stimulates antibody production.
• Antibody: A protein produced by the immune system that targets harmful substances.
• Humoral Immunity: Immunity provided by antibodies in the body fluids.
• Cell Mediated Immunity: Immunity provided by the T lymphocytes.

Immune system structures

• Bone Marrow: Produces white blood cells (WBCs).
• Lymphoid Tissues: Sites of WBC activity.
  • Spleen: Filters blood, removing old and injured red blood cells.
  • Lymph nodes: Remove foreign material from the lymph system.
• Physical and Chemical Barriers: First line of defense.
  • Physical: Skin, mucous membranes, cilia of the respiratory tract.
  • Chemical: Mucus, gastric secretions, enzymes in tears and saliva.

White Blood Cells (WBCs)

• Granular Leukocytes (Granulocytes):
  • Neutrophils: Most abundant WBC, first responders to inflammation.
  • Eosinophils: Fight multicellular parasites.
  • Basophils: Involved in allergic reactions.
  • Mast cells: Role in wound healing and allergic reactions.
• Nongranular Leukocytes:
  • Monocytes/Macrophages: Larger phagocytic cells than granulocytes.
  • Lymphocytes:
    • B cells: Responsible for humoral immunity, producing antibodies.
    • T cells: Responsible for cell-mediated immunity.
      • Helper T cells: Stimulate B cells and killer T cells.
      • Killer T cells: Destroy infected or cancerous cells.

Types of Immunity

• Natural/Nonspecific immunity: Present at birth.
• Acquired/Specific immunity: Develops after birth.
  • Active acquired immunity: Develops after exposure to pathogens.
    • Examples: Vaccination, infectious disease.
  • Passive acquired immunity: Temporary immunity from external sources.
    • Examples: Maternal antibodies, immune globulin injections.

Human Immunodeficiency Virus (HIV)

• A retrovirus that attacks the human body's immune system, specifically CD4+ cells.
• Transmission:
  • Body fluids: blood, seminal fluid, vaginal secretions, amniotic fluid, breast milk.
  • Mother-to-child: in utero, during birth, breast feeding.
  • Sharing needles, unsafe sexual contact, organ transplantation.

HIV Prevention:

• Use condoms.
• Reduce the number of sexual partners.
• Don't share needles, razors, toothbrushes, or blood contaminated articles.
• Pre-Exposure Prophylaxis (PrEP): Daily medication to prevent HIV infection.
• Avoid anal intercourse.
• Get tested regularly.

HIV Prevention for Healthcare Providers:

• Standard Precautions: Hand hygiene, personal protective equipment.
• Post-Exposure Prophylaxis (PEP): Antiretroviral medications taken within 72 hours of potential exposure.

HIV Pathophysiology:

• HIV cannot replicate without a host cell.
• HIV uses a CD4+ cell to reproduce.

1. Attachment/Binding: HIV glycoproteins bind to the CD4 receptor on the host cell.
2. Uncoating/Fusion: HIV releases its genetic material (RNA and enzymes) into the CD4 cell.
3. DNA synthesis: Reverse transcriptase converts HIV RNA into DNA.
4. Integration: Integrase inserts the viral DNA into the host cell’s DNA.
5. Transcription: The integrated DNA produces messenger RNA (mRNA) to build new viruses.
6. Translation: mRNA creates proteins and enzymes necessary for viral replication.
7. Cleavage: Protease enzyme cuts the polyprotein chain into individual components.
8. Budding: New proteins and viral RNA assemble at the cell membrane, forming new viruses.

HIV Stages:

• Acute Stage:
  • Characterised by flu-like symptoms (aches, fever, fatigue etc.).
  • Occurs weeks to a month after infection.
  • High viral load, CD4 count is still high.
• Chronic Stage (Asymptomatic Stage):
  • HIV remains undetected for many years.
  • Viral load is low, but HIV replicates.
  • CD4 count is typically above 500 cells/mm^3.