C5

Definition

C5, or complement component 5, is a protein that plays a crucial role in the immune response by being a part of the complement system. It is involved in both innate and adaptive immunity, helping to promote inflammation, opsonization, and cell lysis, making it a key player in the body’s first line of defense against pathogens.

5 Must Know Facts For Your Next Test

1. C5 is cleaved into C5a and C5b, where C5a acts as an anaphylatoxin that recruits immune cells to sites of infection, while C5b initiates the formation of the membrane attack complex (MAC).
2. The activation of C5 is critical for promoting inflammatory responses, which are essential for effective pathogen clearance.
3. C5 deficiency can lead to increased susceptibility to infections, particularly from encapsulated bacteria due to impaired opsonization.
4. In certain autoimmune diseases, excessive activation of C5 may contribute to tissue damage due to uncontrolled inflammation.
5. Therapeutic interventions targeting C5, such as monoclonal antibodies, have been developed to manage conditions like paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome.

Review Questions

• How does C5 contribute to both inflammation and opsonization in the immune response?
  • C5 plays a dual role in the immune response by being cleaved into C5a and C5b. C5a serves as a potent anaphylatoxin that promotes inflammation by attracting immune cells to sites of infection. Meanwhile, C5b is involved in forming the membrane attack complex, which aids in opsonization by marking pathogens for phagocytosis. This coordinated action enhances the body's ability to respond effectively to infections.
• Discuss the clinical significance of C5 deficiencies and how they impact susceptibility to infections.
  • C5 deficiencies are clinically significant as they result in increased vulnerability to infections, especially from encapsulated organisms like Streptococcus pneumoniae and Neisseria meningitidis. Without adequate levels of C5, the complement cascade cannot proceed effectively, leading to reduced opsonization and impaired immune cell recruitment. This can cause recurrent infections and serious health complications, highlighting the importance of this component in maintaining immune defense.
• Evaluate the implications of targeting C5 in therapeutic interventions for autoimmune conditions.
  • Targeting C5 with specific therapies has significant implications for managing autoimmune conditions where excessive complement activation leads to tissue damage. By inhibiting C5, these therapies can reduce inflammatory responses and limit tissue injury caused by dysregulated immune activity. This approach has been shown to improve patient outcomes in conditions like paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome by controlling complement-mediated damage while preserving overall immune function.

Related terms

Complement System: A group of proteins that work together to enhance the immune response by marking pathogens for destruction, promoting inflammation, and directly killing cells.

Opsonization:

The process by which pathogens are marked for ingestion and destruction by phagocytes, enhancing the efficiency of the immune response.

Anaphylatoxins: Small peptides produced during complement activation that promote inflammation and can lead to an increase in vascular permeability and recruitment of immune cells.