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The MBL2 gene provides instructions for making a protein that assembles into a protein complex called mannose-binding lectin (MBL). This protein complex plays an important role in the immune system's response to foreign invaders (pathogens)

MBL is involved in pattern recognition in the first line of immune defense. MBL recognises patterns of carbohydrates (sugars) found on the surface of a large number of pathogenic microorganisms. Binding of MBL to a microorganism results in the activation of the immune system. Mannose-binding lectin recognises and attaches (binds) to sugars such as mannose, fucose, and glucose, that are found on the surface of bacteria, viruses, and yeast. This binding turns on (activates) the complement system, which is a group of immune system proteins that work together to destroy pathogens, trigger inflammation, and remove debris from cells and tissues. The attachment of mannose-binding lectin also targets the pathogen to be engulfed and broken down by special immune cells. Recognition of foreign invaders by mannose-binding lectin provides one of the body's first lines of defense against infection.

Several common mutations of the MBL2 gene can lead to a condition called mannose-binding lectin deficiency. People with this condition have low levels of mannose-binding lectin and may be susceptible to recurrent infections. Several of the disease-associated mutations occur in a region of the MBL2 gene known as exon 1 and result in a change to single protein building blocks (amino acids) in the mannose-binding lectin subunit. Other mutations occur in an area of DNA near the MBL2 gene called the promoter region, which helps control the production of the mannose-binding lectin subunit.

Mannose-binding lectin deficiency is a condition that affects the immune system. People with this condition have low levels of mannose-binding lectin in their blood. These individuals are prone to recurrent infections, including infections of the upper respiratory tract and other body systems. People with this condition may also contract more serious infections such as pneumonia and meningitis. Depending on the type of infection, the symptoms caused by the infections vary in frequency and severity. Infants and young children with mannose-binding lectin deficiency seem to be more susceptible to infections, but adults can also develop recurrent infections. In addition, affected individuals undergoing chemotherapy or taking drugs that suppress the immune system are especially prone to infections. Low MBL activity does protect against certain types of infection, however, such as tuberculosis. 

The following cofactors have an agonist impact on mannose-binding lectin (MBL) protein:

  • Vitamin A (retinol)
  • Garlic
  • Wild garlic
  • Beta-glucans
  • Larch Arabinogalactan

This means that these substances cause the same action as the substance that normally binds to the receptor, upregulating its function.