Can be more efficient when activated by specific antibody produced by the adaptive immune response. The specific antibody attaches to the pathogen to form an antibody-antigen complex, activating mutlipart protein C1. C1 then recruits other complement proteins in a cascading manner.

Austin Community College

University of Notre Dame

Three pathways that trigger complement activation include:
- Alternative pathway
- Classical pathway
- Lectin pathway

(Photo credits in References)

Pathways Triggering Complement Activation

Antibodies have many functions to help facilitate an adaptive immune response:
- Antibody-dependent cell-mediated cytotoxicity (ADCC)
- Opsonization
- Neutralization 
- Agglutination
- Activation of The Complement System

Functions of Antibodies

OpenStax Concepts of Biology provides the necessary breadth and depth for core Biology concepts.

Link: https://openstax.org/details/books/concepts-biology/

OpenStax Biology 2nd Edition

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Pathways Triggering Complement Activation Figure (Figure 17.9). Reprinted from OpenStax Microbiology (p. 696), by N. Parker, M. Shneegurt, A.-h. Thi Tu, B. M. Forester, and P. Lister, 2016, Rice University. Copyright 2016 by Rice University.

Pathways Triggering Complement Activation Figure

Initiated by the spontaneous activation of complement protein C3, the hydrolysis of which forms C3a and C3B. With invaders absent: C3B degraded in a hydrolysis reaction. Without invaders present: C3b attaches to invaders and recruits other complement proteins.

Complement Activation: Alternative Pathway

Complement Activation: Classical Pathway

Similar to classical pathway, but involves lectin. Lectin, an acute-phase protein, triggers the cascade by binding to carbohydrates on the microbial surface.

Complement Activation: Lectin Pathway

Despite the differences in complement activation pathways, they all share and provide four protective outcomes: opsonization, inflammation, chemotaxis, and cytolysis.

Common Outcomes of Complement Activation Pathways

Neutralization involves the binding of certain antibodies (IgG, IgM, or IgA) to epitopes on the surface of pathogens or toxins, preventing their attachment to cells.

Neutralization

Agglutination or aggregation occurs when pathogens are cross linked by antibodies to create large aggregates. When large aggregates develop phagocytes can ingest them easier. The pentameric structure of IgM provides ten Fab binding sites per molecule, making it the most efficient antibody for agglutination.

Agglutination

The coating of a pathogen with opsonin, tagging it for phagocytic cells to easily recognize and destroy it

Learn Before

Related