- Maarten W Bronkhorst, MD, FEBS, FRCS
Maarten W Bronkhorst, MD, FEBS, FRCS
- Attending Trauma Surgeon
- Haaglanden Medical Center
- Lee H Bouwman, MD, PhD, FEBVS
Lee H Bouwman, MD, PhD, FEBVS
- Vascular Surgeon
- Atrium Medical Center, Heerlen, The Netherlands
Mannose-binding lectin (MBL), also known as mannan-binding protein (MBP), is a protein that specifically binds or crosslinks carbohydrates. Lectins are involved in complement activation via the lectin pathway. The complement system provides immediate defense against infection and has proinflammatory effects; it is considered part of both the innate and adaptive immune systems.
This topic review will discuss the genetic defects and polymorphisms of the MBL2 gene and the function of the MBL protein. The diagnosis of MBL deficiency, diseases associated with both low and high levels of MBL, and other aspects of the complement system are discussed separately. (See "Mannose-binding lectin deficiency" and "Complement pathways" and "Overview and clinical assessment of the complement system" and "Regulators and receptors of the complement system".)
THE MBL GENE
In many animals, there are two MBL genes, MBL1 and MBL2, that code for a functional product. However, in humans, the MBL1 gene, MBL1P1, is a pseudogene (ie, it does not produce a functional protein) . The two MBL genes are most likely the result of a gene-duplication event .
The human MBL protein is encoded by four exons. The MBL2 gene also contains an extra exon approximately 1 kb upstream of exon 1, named exon 0, which may initiate transcription of the MBL2 gene . Gene expression is primarily regulated by several consensus elements in the promoter region .
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