Understanding the Immune System: Macrophages, T Cells, Antigens, and ELISA

Posted on May 5, 2024 in Biology

Understanding the Immune System: Macrophages and T Cells

Macrophages: The Body’s Scavengers

Macrophages are vital white blood cells that act as the body’s defense system, engulfing and eliminating pathogens, dead cells, and debris. They are found throughout the body, particularly in tissues where they act as sentinels against infection.

Structure of Macrophages

  • Shape and Size: Large, irregularly shaped cells (15-30 micrometers).
  • Cytoplasm: Contains lysosomes with enzymes for breaking down ingested material.
  • Surface Receptors: Recognize and bind to specific molecules, including pathogens.
  • Nucleus: Large and irregularly shaped.

Functions of Macrophages

  1. Phagocytosis: Engulfing and digesting pathogens and debris.
  2. Antigen Presentation: Presenting antigens to T cells to activate the immune response.
  3. Cytokine Production: Releasing signaling molecules to regulate the immune response.
  4. Tissue Repair: Removing debris and promoting the growth of new cells.
  5. Immune Regulation: Maintaining immune system balance.

Types of Macrophages

  • Tissue-Resident Macrophages: Maintain tissue homeostasis and respond to local infections.
  • Monocyte-Derived Macrophages: Derived from circulating monocytes and migrate to tissues during inflammation.

T Cells: The Immune System’s Defenders

T cells, or T lymphocytes, are another type of white blood cell crucial for recognizing and attacking infected cells, cancer cells, and pathogens. They mature in the thymus gland and are characterized by the presence of T-cell receptors (TCRs) on their surface.

Structure of T Cells

T cells have TCRs that allow them to recognize specific antigens. They also have surface proteins like CD4 and CD8, which classify them into different subtypes.

Types of T Cells

  1. Helper T cells (CD4+ T cells): Coordinate the immune response and activate other immune cells.
  2. Cytotoxic T cells (CD8+ T cells): Directly kill infected or abnormal cells.
  3. Regulatory T cells (Tregs): Regulate the immune response and prevent it from becoming too strong.

Functions of T Cells

  1. Antigen Recognition: Recognize antigens presented by antigen-presenting cells (APCs).
  2. Activation: Increase in number upon activation.
  3. Differentiation: Develop into various subtypes with specific functions.
  4. Effector Functions: Perform specific tasks depending on their subtype.
  5. Memory: Some T cells become memory T cells, providing long-lasting immunity.

Antigenicity and Immunogenicity: Understanding Immune Responses

Antigenicity refers to the ability of a substance to bind to an antibody or T-cell receptor. Immunogenicity, on the other hand, refers to the ability of an antigen to induce an immune response.

Types of Antigens

  • Self-antigens: Antigens from the body’s own cells.
  • Foreign antigens: Antigens from outside the body, such as pathogens.
  • Autoantigens: Self-antigens mistakenly targeted by the immune system in autoimmune diseases.

Factors Influencing Immunogenicity

  • Size and complexity
  • Foreignness
  • Chemical composition
  • Route of administration
  • Adjuvants
  • Genetic factors

ELISA Technique: Detecting Molecules in Samples

ELISA (Enzyme-Linked Immunosorbent Assay) is a widely used technique to detect specific proteins, antibodies, or antigens in a sample.

ELISA Principle

  1. Coating: Coating a microplate with a specific antigen or antibody.
  2. Blocking: Preventing non-specific binding.
  3. Sample and Controls: Adding the sample containing the target molecule.
  4. Primary Antibody Binding: Target molecule binds to the coated antigen/antibody.
  5. Detection: Adding a secondary antibody linked to an enzyme.
  6. Substrate Addition: Adding a substrate that produces a detectable signal.
  7. Signal Measurement: Measuring the signal intensity to quantify the target molecule.

Types of ELISA

  • Direct ELISA
  • Indirect ELISA
  • Sandwich ELISA
  • Competitive ELISA

Applications of ELISA

  • Medical Diagnostics
  • Research

Nomenclature and Classification of Viruses

Nomenclature and classification are essential for organizing and studying viruses.

Virus Nomenclature

  • Viruses are named based on morphology, genetic makeup, transmission, and diseases caused.
  • The International Committee on Taxonomy of Viruses (ICTV) oversees naming and classification.

Virus Classification

  • Viruses are classified based on genetic material, genome structure, replication, host range, and morphology.
  • The Baltimore classification system groups viruses into seven classes based on nucleic acid and replication strategy.
  • Viruses can also be classified by host type and diseases caused.