New Immunodeficiency due to FCN3 gene mutation for Ficolin-3, a recognition molecule in lectin pathway of complement

A NEJM report describes a man with repeated severe bacterial pulmonary infections, bronchiectasis, pulmonary fibrosis, warts, and a cerebral abscess.

He was homozygous for a variant of the FCN3 gene, which encodes ficolin-3. A lack of ficolin-3 may cause immunodeficiency disease.

Ficolin (collagen/fibrinogen domain containing lectin) 2 (hucolin). Image source: Wikipedia, public domain.

Overview of the innate immune system (a mind map).

There are 3 pathways for activation of complement:


Mannose-binding lectin (MBL)

Mannose-binding lectin (MBL). Image source: Wikipedia.

The 3 pathways (CAM) converge at the point of cleavage of C3. Then C3b becomes an acceptor site for C5, and C5-9 form the membrane attacking complex (MAC). Thus, CAM leads to MAC:


A complement protein attacking an invader. Image source: Wikipedia.

Classical and alternative complement pathways. Image source: Wikipedia.

Immunodeficiency Associated with FCN3 Mutation and Ficolin-3 Deficiency. NEJM, 2009.
NEJM figure.
Complement System


Classical Pathway Complement System

Alternative Pathway Compliment System

The Complement System.

Complement Proteins

Figure 1 - The complement system as a bridge between innate and adaptive immunity. Nature.
The three major complement activation pathways
Overview of the Complement System

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