Immune System: Cells, Antibodies, and Defense Mechanisms

Posted on May 5, 2024 in Biology

Cells of the Immune System

The immune system is a complex network of cells and proteins that protects the body from infection and disease. Key cells include:

White Blood Cells (Leukocytes)

Leukocytes are divided into two main types:

  • Phagocytes: Engulf and digest pathogens and debris. Examples include neutrophils, monocytes, and macrophages.
  • Lymphocytes: Responsible for specific immune responses. Main types are B cells and T cells.

B Cells and T Cells

  • B cells: Produce antibodies that neutralize specific pathogens.
  • T cells: Directly attack and destroy infected cells. Types include helper T cells, cytotoxic T cells, and regulatory T cells.

Other Immune Cells

  • Natural killer (NK) cells: Kill infected and cancer cells.
  • Dendritic cells: Initiate adaptive immune responses.
  • Mast cells: Involved in inflammation and defense against parasites.
  • Eosinophils and basophils: Involved in inflammation and defense against parasites.

HIV: Life Cycle and Structure

Life Cycle of HIV

  1. Attachment and Entry: HIV attaches to a CD4 cell and releases its genetic material.
  2. Reverse Transcription: HIV converts its RNA into DNA.
  3. Integration: Viral DNA integrates into the host cell’s DNA.
  4. Transcription and Translation: Viral DNA is transcribed into RNA, which is translated into viral proteins.
  5. Assembly: New viral particles are assembled.
  6. Budding: New viral particles bud off from the host cell.
  7. Maturation: Viral particles become infectious.

Structure of HIV

  • Envelope: Outer layer with glycoproteins for attachment.
  • Capsid: Protein shell enclosing viral RNA and enzymes.
  • RNA: HIV’s genetic material.
  • Enzymes: Essential for replication (e.g., reverse transcriptase, integrase).
  • Proteins: Involved in various stages of the virus’s life cycle.

Antibodies: Properties and Biological Roles

Antibodies, or immunoglobulins (Ig), are proteins that recognize and neutralize antigens.

Classes of Immunoglobulins

  • IgG: Most abundant, provides long-term immunity.
  • IgM: First produced during an immune response, effective at agglutination.
  • IgA: Found in mucosal areas, provides mucosal immunity.
  • IgE: Involved in allergic reactions and defense against parasites.
  • IgD: Role not fully understood, possibly involved in B cell activation.

Secondary Lymphoid Organs: Lymph Nodes and Spleen

Lymph Nodes

Lymph nodes filter lymph fluid and facilitate immune responses.

Spleen

The spleen filters blood and initiates immune responses to blood-borne antigens.

Lineage Host System of Classification

This system classifies organisms based on evolutionary relationships.

Main Categories

  1. Domain: Archaea, Bacteria, Eukarya
  2. Kingdom: Animalia, Plantae, Fungi, etc.
  3. Phylum: Chordata, Arthropoda, etc.
  4. Class: Mammalia, Aves, etc.
  5. Order: Carnivora, Primates, etc.
  6. Family: Felidae, Canidae, etc.
  7. Genus: Panthera, Canis, etc.
  8. Species: Panthera leo, Canis lupus, etc.

Antigens and Factors Affecting Immune Response

Antigens are molecules that induce an immune response.

Factors Affecting Immune Response

  • Nature of the antigen
  • Dose of the antigen
  • Route of exposure
  • Genetic factors
  • Age
  • Previous exposure
  • Health status
  • Adjuvants

Viruses: Definition and Classification

Viruses are microscopic infectious agents that replicate inside living cells.

Classification of Viruses

  • Type of genetic material: DNA or RNA
  • Shape of the capsid: Helical, icosahedral, or complex
  • Presence or absence of an envelope
  • Mode of replication
  • Host range: Animals, plants, bacteria, etc.