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chemotaxis

ImmunologyImmune SystemHematologic System

Summary

Chemotaxis is the directed movement of cells, especially leukocytes, along a chemical gradient toward a site of infection or inflammation. Key chemotactic factors include C5a, IL-8, LTB4, and bacterial N-formylmethionine peptides. Defects in chemotaxis (e.g., Leukocyte Adhesion Deficiency, Chediak-Higashi syndrome) lead to recurrent infections.

Detail

Chemotaxis is a critical step in the innate immune response, occurring after leukocytes marginate and adhere to the vascular endothelium. The process involves: (1) rolling (mediated by selectins), (2) tight adhesion (mediated by integrins, upregulated by chemokines), (3) transmigration/diapedesis through the endothelium (mediated by PECAM-1/CD31), and (4) chemotaxis along a chemical gradient toward the site of injury or infection.

Major chemoattractants include: - C5a (complement cascade) - IL-8 (CXCL8) - recruits neutrophils - Leukotriene B4 (LTB4) - arachidonic acid pathway - Bacterial products (N-formylmethionine peptides) - Platelet-activating factor (PAF)

These chemoattractants bind to G-protein coupled receptors on leukocytes, activating signaling cascades (via Rho GTPases like Rac and Cdc42) that cause actin polymerization and pseudopod formation, allowing directed ameboid movement toward the highest concentration of the chemotactic signal.

Clinical relevance includes several immunodeficiency disorders affecting chemotaxis: - Leukocyte Adhesion Deficiency (LAD) Type 1: CD18 integrin defect, impairs firm adhesion, presents with recurrent bacterial infections, delayed umbilical cord separation, absence of pus - Chediak-Higashi Syndrome: LYST gene mutation affecting lysosomal trafficking, causes impaired chemotaxis, giant granules in leukocytes, partial albinism, recurrent pyogenic infections - Job Syndrome (Hyper-IgE syndrome): STAT3 mutation, impaired neutrophil chemotaxis, characterized by eczema, recurrent skin/lung infections, elevated IgE

Understanding chemotaxis is essential for understanding the pathophysiology of inflammation, wound healing, and various primary immunodeficiency disorders tested on USMLE Step 1.

Sources

  • First Aid for the USMLE Step 1
  • Robbins and Cotran Pathologic Basis of Disease
  • Janeway's Immunobiology

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