The current coronavirus disease (COVID-19) is caused by a virus, Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2). SARS-CoV-2 is related to its predecessor, Severe Acute Respiratory Syndrome CoronaVirus (SARS-CoV-1), which caused the SARS outbreak between 2002 and 2004. [1]
After the SARS-CoV-1 outbreak, research into antiviral compounds against coronaviruses indicated “[t]he strongest anti-coronavirus activity was found predominantly among the mannose-binding lectins” [2a]. Those researchers concluded mannose binding lectins interfered with SARS-CoV-1 during virus entry and virus release. [2a, 2b] Virus entry is the earliest stage of infection when a virus comes into contact with a new host cell. After reproducing within the new host cell, virus release occurs so that the new virus “babies” can go infect new host cells. By interfering with both of those stages of the coronavirus life cycle, mannose binding lectins can both prevent cells from becoming infected and prevent an infected cell from spreading to more cells.
As SARS-CoV-2 is related to SARS-CoV-1, it stands to reason that what’s effective against the first will likely be effective against the second.
What are mannose binding lectins and why are they important?
Mannose binding lectins are lectins. (I know, not helpful yet.) Lectins are proteins very common in nature and found in many foods like beans and grains. There are many types of lectins so it’s important to focus first on the mannose binding lectin. [3]
Research has also shown that a deficiency of mannose binding lectin affects the immune system and makes it much easier for people to develop infections, especially respiratory tract infections [4, 5, 6, 7] which are consistent with the symptoms for COVID-19. “Mannose-binding lectin plays an important role in the body’s immune response by attaching to foreign invaders such as bacteria, viruses, or yeast and turning on (activating) the complement system. The complement system is a group of immune system proteins that work together to destroy foreign invaders (pathogens), trigger inflammation, and remove debris from cells and tissues.” [4]
Basically, mannose binding lectins help our immune system fight viruses. And, they’re particularly good at fighting coronaviruses like SARS-CoV-1.
Where can we get some mannose binding lectins?
Mannose binding lectins are common in many plants [8, 9, 10] including:
- legumes (like beans, peas, chickpeas, lentils, soybeans, and peanuts),
- artichokes
- bananas
- rice
- onions
- leeks (especially potent against SARS-CoV)
- shallots
- taro
While mannose binding lectins demonstrated the most anti-coronavirus activity, researchers found almost half of the lectins tested (15 out of 33) had antiviral properties against SARS-CoV. [2c] Since so many lectins have antiviral properties, we should look to supplement ourselves with foods high in lectins.
As lectins, including mannose binding lectins, are common in many plants, we should simply eat more fruits and vegetables to increase our resistance to the coronavirus. Fruits and vegetables are not only generally good for us; they might even help you fight the coronavirus.
Disclaimer: Opinions are my own and not those of Google.
References
[1] “Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin that surfaced in the early 2000s caused by severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first-identified strain of the SARS coronavirus species severe acute respiratory syndrome-related coronavirus (SARSr-CoV). The syndrome caused 2002–2004 SARS outbreak. … In 2019, a related virus strain, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was discovered. This new strain causes COVID-19, a disease which brought about the ongoing 2019–20 coronavirus pandemic.” https://en.wikipedia.org/wiki/Severe_acute_respiratory_syndrome
[2a] “A unique collection of 33 plant lectins with different specificities were evaluated. The plant lectins possessed marked antiviral properties against both coronaviruses with EC50 values in the lower microgram/ml range (middle nanomolar range), being non-toxic (CC50 ) at 50–100 g/ml. The strongest anti-coronavirus activity was found predominantly among the mannose-binding lectins. … A significant correlation (with an r-value of 0.70) between the EC50 values of the 10 mannose-specific plant lectins effective against the two coronaviruses was found. In contrast, little correlation was seen between the activity of other types of lectins. Two targets of possible antiviral intervention were identified in the replication cycle of SARS-CoV. The first target is located early in the replication cycle, most probably viral attachment, and the second target is located at the end of the infectious virus cycle.”
[2b] “In conclusion, we identified a variety of plant lectins as antiviral compounds against the SARS-CoV and the FIPV. The lectins most probably interfere with the glycans on the spike protein during virus entry and virus release.”
[2c] “Out of the 33 plant lectins tested against SARS-CoV and FIPV, 15 lectins had antiviral properties against both Coronaviruses; 5 plant lectins were active only against SARS-CoV and 2 lectins showed solely activity against FIPV. … The most potent lectin against the SARS-CoV-induced cytopathicity is the mannose-specific plant lectin isolated from leek (APA) with an EC50 of 0.45 μg/ml and a selectivity index of >222. … Out of 33 plant lectins evaluated, 15 showed antiviral properties against both SARS-CoV and FIPV, and 8 plant lectins showed no anti-coronavirus activity. The lectins with anti-coronaviral activity included mannose-, glucose-, galactose-, N-acetyl glucosamine- and N-acetyl galactosamine-specific agglutinins.”
Plant lectins are potent inhibitors of coronaviruses by interfering with two targets in the viral replication cycle (2007).
[3] Lectin list via Wikipedia cite
[4] “People with mannose-binding lectin deficiency can develop infections of the upper respiratory tract and other body systems. Individuals 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.”
Mannose-binding lectin deficiency
[5] “Several studies have shown that deficiency of MBL increases the overall susceptibility of an individual to infectious disease. The most striking example of this is the association of acute respiratory tract infections with MBL deficiency in early childhood.”
The role of mannose-binding lectin in health and disease. [PubMed.gov, ScienceDirect]
[6] “The innate immune system, which includes mannose-binding lectin (MBL), recognizes a broad range of molecular patterns on a broad range of infectious agents and is able to distinguish them from self. MBL is a liver-derived serum protein and is secreted into the serum, where it can activate an immune response before the induction of antigen-specific immunity. Circumstantial evidence in human populations suggests that low serum levels of MBL predispose to infection. … Our results suggest that MBL plays an important role as a first-line host defense against certain infectious agents. In addition, it is likely that MBL is a key regulator of inflammation beyond expected roles in the infection.”
The Role of the Mannose-Binding Lectin in Innate Immunity
[7] “Mannose-binding lectin (MBL), also called mannan-binding lectin or mannan-binding protein (MBP), is a lectin that is instrumental in innate immunity… It is produced in the liver as a response to infection, and is part of many other factors termed acute phase proteins.” https://en.wikipedia.org/wiki/Mannan-binding_lectin
[8] “Mannose-specific lectins are widely distributed in higher plants and are believed to play a role in recognition of high-mannose type glycans of foreign micro-organisms or plant predators. Structural studies have demonstrated that the mannose-binding specificity of lectins is mediated by distinct structural scaffolds. The mannose/glucose-specific legume (e.g., Con A, pea lectin) exhibit the canonical twelve-stranded beta-sandwich structure. In contrast to legume lectins that interact with both mannose and glucose, the monocot mannose-binding lectins (e.g., the Galanthus nivalis agglutinin or GNA from bulbs) react exclusively with mannose and mannose-containing N-glycans. These lectins possess a beta-prism structure. More recently, an increasing number of mannose-specific lectins structurally related to jacalin (e.g., the lectins from the Jerusalem artichoke, banana or rice), which also exhibit a beta-prism organization, were characterized. Jacalin itself was re-defined as a polyspecific lectin which, in addition to galactose, also interacts with mannose and mannose-containing glycans. Finally the B-chain of the type II RIP of iris, which has the same beta-prism structure as all other members of the ricin-B family, interacts specifically with mannose and galactose. This structural diversity associated with the specific recognition of high-mannose type glycans highlights the importance of mannose-specific lectins as recognition molecules in higher plants.”
Mannose-binding plant lectins: different structural scaffolds for a common sugar-recognition process.
[9] “Two novel lectins were isolated from roots and leaves of garlic. Characterization of the purified proteins indicated that the leaf lectin ASAL is a dimer of two identical subunits of 12 kDa, which closely resembles the leaf lectins from onion, leek and shallot with respect to its molecular structure and agglutination activity.”
Isolation, characterization and molecular cloning of the mannose-binding lectins from leaves and roots of garlic (Allium sativum L.)
[10] Plant Lectins: Versatile Proteins with Important Perspectives in Biotechnology
