Ficolin3

Ficolin-3, also known as H-ficolin, is a soluble pattern recognition molecule that participates in the lectin pathway of the complement system. It is encoded by the FCN3 gene in humans.

Structurally, ficolin-3 consists of a collagen-like domain and a C-terminal fibrinogen-like recognition domain and forms multimeric complexes in the bloodstream. It is primarily produced by the liver and secreted into plasma, where it contributes to the constitutive defense against infection.

Functionally, ficolin-3 recognizes acetylated compounds and other surface patterns on various microorganisms. Upon binding its targets, it associates with MASP-1, MASP-2, and MASP-3, activating the lectin pathway. This activation leads to cleavage of C4 and C2, formation of the C3 convertase, and downstream effects including opsonization, inflammation, and, ultimately, microbial lysis.

Clinical significance of ficolin-3 centers on innate immunity. Deficiency or low circulating levels of ficolin-3, which can result from FCN3 genetic variants or other factors, have been associated with increased susceptibility to infections, particularly in infancy and early childhood, and may contribute to sepsis risk in vulnerable individuals. However, ficolin-3 is one component of a complex immune system, and clinical outcomes typically reflect the combined function of multiple pathways.

Research into ficolin-3 continues to explore its potential as a biomarker for infection risk and immune competence, as well as its broader role in host defense and inflammatory processes.