Makindo Medical Notes

Related Subjects: |Neutropenia |Neutropenic Sepsis |Neutrophils

Neutrophils are a type of white blood cell and the most abundant type of granulocytes. They play a crucial role in the innate immune system by defending the body against infections, particularly bacterial infections.

Anatomy and Structure

• Origin:
  • Produced in the bone marrow from hematopoietic stem cells.
• Structure:
  • Multilobed nucleus (typically 2-5 lobes), giving them the name "polymorphonuclear leukocytes" (PMNs).
  • Contain granules in their cytoplasm filled with enzymes and antimicrobial proteins.

Functions of Neutrophils

• Phagocytosis:
  • Engulf and digest pathogens and debris.
  • Form phagosomes that fuse with lysosomes to kill and degrade ingested materials.
• Degranulation:
  • Release antimicrobial proteins and enzymes from their granules to kill pathogens.
  • Types of granules include azurophilic (primary) granules, specific (secondary) granules, and tertiary granules.
• Neutrophil Extracellular Traps (NETs):
  • Release networks of chromatin fibers decorated with antimicrobial proteins to trap and kill pathogens extracellularly.
• Chemotaxis:
  • Migrate towards sites of infection or inflammation in response to chemical signals (e.g., chemokines, cytokines).

Role in the Immune Response

• Innate Immunity:
  • First responders to microbial infection and injury.
  • Provide a rapid response to invading pathogens.
• Inflammatory Response:
  • Recruitment to infection sites contributes to inflammation and the containment of pathogens.
  • Release of pro-inflammatory cytokines amplifies the immune response.

Clinical Relevance

• Neutropenia:
  • Abnormally low neutrophil count, increasing susceptibility to infections.
  • Causes include bone marrow disorders, chemotherapy, certain medications, and autoimmune diseases.
  • Symptoms: Frequent infections, fever, and mouth ulcers.
• Neutrophilia:
  • Abnormally high neutrophil count, often a response to infection, inflammation, or stress.
  • Can also be seen in myeloproliferative disorders and certain types of leukaemia.
  • Symptoms: Fever, inflammation, and elevated white blood cell count.
• Chronic Granulomatous Disease (CGD):
  • Genetic disorder affecting neutrophil function, specifically their ability to produce reactive oxygen species to kill pathogens.
  • Results in recurrent bacterial and fungal infections.
  • Symptoms: Persistent infections, granuloma formation, and inflammation.
• Sepsis:
  • Systemic inflammatory response to infection leading to organ dysfunction.
  • Neutrophils play a central role in the early stages of sepsis by responding to and attempting to eliminate the infection.
  • Symptoms: Fever, chills, rapid breathing, confusion, and potential organ failure.

Summary

Neutrophils are essential components of the innate immune system, playing a critical role in the body's defense against infections. They are involved in phagocytosis, degranulation, and the formation of neutrophil extracellular traps (NETs). Understanding their functions and clinical relevance is vital for diagnosing and managing conditions related to immune response and infections.