How Is CF Mucus Different From Non-CF Mucus?

When people without cystic fibrosis (CF) think of CF, they likely focus on the hallmark characteristic of the condition: mucus. It is known that CF mucus is thick and sticky and can therefore block passages in the lungs, and impact breathing.¹ One Cystic-Fibrosis.com advocate describes her experience with mucus as the following:

The mucus can get so bad that I feel like I am drowning in my own body, suffocating by the very thing I so desperately try to get rid of. Mucus can range from thick to watery. Each and every time, it hurts, it burns, and it’s agonizing to deal with.

However, beyond this, not much is known about how CF-mucus differs from non-CF mucus. For this topic, we will focus on the mucus found in the respiratory system.

Mucus, phlegm, and sputum

Mucus is defined as the "heterogeneous, adhesive, viscoelastic gel produced by goblet cells and submucosal glands."² Mucous is meant to act as a barrier between the internal and external environment, a barrier meant to protect against foreign substances.³ The barrier traps small particles that may be harmful. Another important role of mucus is to hydrate the airways.

Phlegm is the type of mucus produced in the respiratory tract, whereas sputum is the term used to describe phlegm when coughed up.

Cystic fibrosis mucus characteristics

Overall, CF mucus has the following unique characteristics, compared to non-CF mucus:⁴

• High concentration of neutrophils, the white blood cells which make up the body's defence system
• Infection with some organisms like Pseudomonas aeruginosa, Staphylococcus aureus, and aspergillus. These organisms can cause pneumonia, Aspergillosis, and other diseases.
• Dehydrated gel matrix

Mucus thickness

Non-CF mucus in the airways is composed of a single gel layer -- this layer is only a few tens micrometers in thickness. To put it into perspective how thin this is, a strand of hair is 100-150 micrometers wide!⁵ In people with cystic fibrosis, however, there is hyper-production of mucus.

It is commonly stated that the primary problem with CF mucus is that it is too thick. However, studies have shown that the viscosity, or thickness, of CF mucus is no greater than that of sputum of people with chronic bronchitis or asthma.⁶

Bacterial content

It is commonly believed that people with cystic fibrosis have mucus filled with bacteria. However, a study demonstrated that on average, non-CF mucus has more bacteria than CF mucus.⁶ There are certainly particular pathogens that seem to be more common in CF mucus than non-CF mucus.

Mucin content

CF mucus is often described as more solid and having a “flake” form. In addition, it has a higher concentration of proteins called mucins.⁷ Mucins make up the main component of mucus and are responsible for the gel-consistency of mucus. Non-CF mucus is composed mainly by two types of mucins: MUC5AC and MC5B.⁶ Interestingly, people with CF have very little of these two mucins. This is why CF sputum is not quite like mucus, but more resembles the physical and chemical nature of pus.

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