The role of complement in danger sensing and transmission

Area of Science:

• Immunology
• Molecular Biology

Background:

• The immune system's primary function is traditionally viewed as self-non-self discrimination.
• Emerging evidence highlights the immune system's role as a complex network for sensing and transmitting danger signals, with self-non-self discrimination being only one aspect.
• The immune system utilizes conserved molecules to recognize microbial and modified self-structures.

Purpose of the Study:

• To review the function and biology of the complement system as an ancient danger-sensing mechanism.
• To explore the role of Toll-like receptors (TLR) in danger recognition and signaling.
• To discuss the interplay between the complement system and TLRs in shaping immune responses.

Main Methods:

• Review of existing literature on the complement system and TLRs.
• Analysis of molecular mechanisms of complement-mediated and TLR-mediated danger sensing.
• Examination of signaling pathways activated by these systems.

Main Results:

• Toll-like receptors (TLR) are membrane-bound pattern-recognition receptors that initiate signaling cascades upon detecting danger signals.
• The complement system, a network of soluble molecules, senses danger through direct binding and proteolytic cascades, generating fragments that activate distinct receptors.
• Complement-mediated danger sensing is crucial for tissue homeostasis during steady-state, infection, and injury.

Conclusions:

• The complement system and TLRs represent ancient and critical components of host defense.
• Cross-talk between the complement system and TLRs is essential for fine-tuning the quality and magnitude of in vivo immune responses.
• A comprehensive understanding of these systems is vital for comprehending immune system function beyond self-non-self discrimination.