A hidden weapon in our own bodies might hold the key to fighting stubborn fungal infections.
Imagine if a protein naturally abundant in your saliva could be harnessed as a potent antifungal treatment. For millions facing opportunistic fungal infections, this prospect is moving from the realm of possibility to tangible reality. At the forefront of this exciting development is CCL28, a multifunctional chemokine that acts as a first line of defense in our mucosal tissues. Recent research reveals its remarkable ability to combat oropharyngeal candidiasis, commonly known as oral thrush, through a rapid and devastating attack on fungal cell membranes—offering new hope in an era of increasing antifungal resistance1 2 .
CCL28, scientifically known as "mucosae-associated epithelial chemokine" (MEC), is a small protein constitutively expressed by epithelial cells in various mucosal tissues including the mouth, colon, salivary gland, mammary gland, and trachea4 . It belongs to the chemokine family, a group of proteins best known for their role as chemoattractants—chemical guides that direct the migration of immune cells to sites of infection or inflammation2 .
For years, scientists understood CCL28 primarily as a signaling molecule that interacts with two specific receptors (CCR3 and CCR10) on immune cells, guiding T-cells and eosinophils to where they're needed most2 4 . However, research over the past decade has uncovered an entirely different function: CCL28 is a potent broad-spectrum antimicrobial agent with particular efficacy against fungal pathogens2 .
What makes CCL28's antimicrobial function so remarkable is its presence in bodily fluids where salt concentrations are relatively low, such as saliva (2-50 mM salt) and milk (5-8 mM salt)2 . In these environments, CCL28 remains highly active against pathogens. This natural distribution suggests our bodies may already be utilizing CCL28's antimicrobial properties as part of our first-line defense system.
The chemokine is especially effective against Candida albicans, the commensal fungus that can turn into an opportunistic pathogen causing oropharyngeal candidiasis1 2 . What's particularly promising is that CCL28 demonstrates efficacy against multiple clinical strains of C. albicans, suggesting its mechanism of action may be effective across different genetic variations of the fungus1 .
The extraordinary antifungal power of CCL28 lies in its ability to directly target and disrupt the integrity of fungal cell membranes. But how does this molecular assassination unfold?
Recent research provides compelling evidence of CCL28's membrane-permeating capabilities1 :
The positively charged CCL28 protein is attracted to and interacts with the negatively charged components of the fungal cell membrane.
Specific structural elements of CCL28, particularly its C-terminal tail, insert into the lipid bilayer of the fungal membrane.
This insertion creates negative Gaussian curvature on model membranes—a technical way of saying it induces structural deformations that compromise membrane integrity.
The disrupted membrane becomes leaky, allowing critical cellular contents to escape and leading to the eventual death of the fungal cell.
This physical mechanism of membrane disruption presents a significant advantage over conventional antifungal drugs. While many existing medications target specific enzymatic pathways that fungi can evolve to bypass, it's much more difficult for pathogens to develop resistance against an attack that fundamentally compromises their structural integrity.
The solution structure of CCL28, solved using nuclear magnetic resonance (NMR) spectroscopy, reveals fascinating structural features that explain its unique functional capabilities2 .
CCL28 adopts the canonical chemokine tertiary fold—a three-stranded antiparallel β-sheet and C-terminal α-helix—but with distinctive characteristics2 . Most notably, it possesses a largely unstructured C-terminal tail that is partially tethered to the protein core by a non-conserved disulfide bond2 .
Interestingly, the C-terminal tail retains significant antifungal activity even when separated from the rest of the protein, though with reduced potency compared to the full-length protein2 . This structural lability—the ability to partially unfold under certain conditions—may be key to CCL28's capacity to perform dual functions in different physiological environments.
To validate CCL28's potential as a therapeutic agent, researchers conducted a crucial series of experiments using a mouse model of oropharyngeal candidiasis1 . The experimental approach was systematic and comprehensive:
Researchers applied purified recombinant CCL28 directly to the oral cavities of immunodeficient mice infected with Candida albicans. These severely immunodeficient mice were chosen to isolate CCL28's direct antifungal effects from potential immune-boosting effects.
The team measured reduction in oral fungal burden by counting colony-forming units (CFUs) after CCL28 treatment. This provided a quantitative measure of how effectively CCL28 cleared the infection.
To understand how CCL28 kills fungal cells, researchers exposed C. albicans to CCL28 and then measured membrane integrity using dye leakage assays, enzyme leakage from damaged cells, and structural changes in artificial model membranes.
The experiment also tested CCL28's effectiveness against multiple clinical strains of C. albicans to ensure broad efficacy.
Finally, researchers examined tissue sections to assess whether CCL28 treatment caused excessive inflammation or altered normal neutrophil recruitment.
The findings from these experiments were striking and consistently demonstrated CCL28's therapeutic potential. The table below summarizes the key outcomes:
| Aspect Tested | Result | Significance |
|---|---|---|
| Fungal Burden | Significant reduction in oral fungal load | Demonstrates therapeutic efficacy in live organisms |
| Killing Speed | Rapid and sustained fungicidal activity | Superior to some clinical antifungal agents |
| Mechanism | Membrane disruption confirmed | Physical mechanism may reduce resistance risk |
| Strain Specificity | Effective against multiple C. albicans strains | Broad applicability against different isolates |
| Safety Profile | No excessive inflammation or altered neutrophil recruitment | Favorable safety and side effect profile |
Perhaps most impressively, both structured and unstructured forms of CCL28 demonstrated fungicidal activity superior to that of some clinical antifungal agents1 . This suggests that even if the protein partially unfolds, it retains significant antifungal capability—an advantage for therapeutic applications where protein stability can be challenging.
The membrane disruption was clearly linked to CCL28's C-terminal tail, as modified versions lacking this functional domain showed reduced ability to permeabilize fungal membranes1 2 .
While much research has focused on CCL28's activity against Candida albicans, its antimicrobial capabilities extend to various other pathogens. Another line of investigation has examined CCL28's effects on periodontal pathogens, with compelling results:
| Pathogen | Effect of CCL28 | 50% Effective Concentration (EC₅₀) |
|---|---|---|
| Porphyromonas gingivalis | Significant killing after 1 hour exposure | ~0.7 μM |
| Aggregatibacter actinomycetemcomitans | Significant killing after 1 hour exposure | ~2.0 μM |
These findings further support CCL28's role as a broad-spectrum antimicrobial peptide rather than a narrow antifungal agent. The ability to target multiple types of pathogens suggests CCL28 might be exploiting a common vulnerability in microbial membranes—possibly related to differences in lipid composition between host and pathogen membranes.
This broad activity profile increases CCL28's potential therapeutic value, as a single agent might be developed to address multiple types of infections.
Advancing our understanding of CCL28 and translating it into clinical applications requires specific research tools and methodologies. The table below outlines key resources and approaches used in studying this multifunctional chemokine:
| Resource/Method | Function in Research | Examples/Specifications |
|---|---|---|
| Recombinant CCL28 | Purified protein for functional assays | E.coli-derived; >96% purity; 13.1 kDa molecular weight4 |
| NMR Spectroscopy | Determining 3D protein structure in solution | Reveals structural lability and domain organization2 |
| Mouse Oropharyngeal Candidiasis Model | Testing therapeutic efficacy in vivo | Uses immunodeficient mice to isolate direct effects1 |
| Membrane Model Systems | Studying mechanism of membrane disruption | Measures induction of negative Gaussian curvature1 |
| Bacterial/Fungal Viability Assays | Quantifying antimicrobial effects | Uses fluorescent dyes to distinguish live/dead pathogens |
These tools have been instrumental in uncovering CCL28's unique properties and will continue to play crucial roles in further development of this promising therapeutic candidate.
The discovery of CCL28's potent antifungal activity through membrane disruption represents a paradigm shift in how we view chemokines—no longer merely as cellular guides, but as direct participants in microbial killing. This expanded understanding opens exciting therapeutic possibilities, particularly for addressing the growing challenge of antifungal resistance.
Potential to simultaneously recruit immune cells and directly kill pathogens
Physical membrane disruption presents a high barrier for pathogen resistance development
Natural human protein with minimal inflammatory side effects
Effective against fungi and multiple bacterial species
While challenges remain in developing stable formulations and delivery methods, CCL28 stands as a promising candidate for the next generation of antimicrobial therapeutics. Its story exemplifies how looking more closely at our own biological systems can reveal sophisticated solutions to medical challenges—in this case, finding that a potent weapon against fungal infections has been present in our saliva all along.
As research continues to unravel the intricacies of CCL28's structure and function, we move closer to harnessing the full potential of this remarkable molecule in the ongoing battle against infectious diseases.