It is a viscous colloid (substance microscopically that is evenly dispersed in another substance) that contains antiseptic enzymes such as lysozyme, immunoglobulins, inorganic salts, proteins such as lactoferrin, and glycoproteins.
Mucous cells are rich in glycoproteins. Glycoproteins, also known as mucins, are produced by goblet cells in the mucous membranes and submucosal glands
In the respiratory system, mucus protects the lungs by filtering out foreign particles that enter it. The process usually happens in the nose during normal breathing. "Phlegm" is a specialized term for mucus that is restricted to the respiratory tract, whereas the term "nasal mucus" describes secretions of the nasal passages.
Immune protection from an unexpected source
Mucus often elicits strong revulsion, but to MIT biological engineer Katharina Ribbeck, it is a fascinating material.
“Without it, we wouldn’t be able to smell, we wouldn’t be able to reproduce, and we would all be the victims of pathogens,” says Ribbeck, who studies the antiviral properties of mucins, the main component of mucus.
Mucus, which coats wet surfaces in the bodies of all animals, is the body’s first line of defense. It allows nutrients, other vital molecules and sperm to enter, but keeps out pathogens such as certain dangerous viruses and bacteria. Ribbeck, the Eugene Bell Career Development Assistant Professor of Biological Engineering, is trying to figure out how mucus achieves this selectivity. Of particular interest is the role of mucins, the major building blocks of mucus.
“Oftentimes they’re regarded as inert scaffold elements, but the picture that is emerging is that they really have an active function in the body’s defense system,” Ribbeck says.
A better understanding of mucins’ immune function could shed light on why certain people are more susceptible to viral or bacterial infections, Ribbeck says. Mucin composition can differ between people, and it also varies depending on factors such as a person’s age, diet and the time of year.
Previous research has shown that mucins — long threadlike proteins with many sugar molecules attached — are abundant in breast milk, protecting infants against viruses such as rotavirus and HIV. To find out if this antiviral role was more general, Ribbeck tested mucins’ ability to block three different viruses from entering cells.
