Protein kinase A signaling regulates immune evasion by shaving and concealing fungal β-1,3-glucan

Summary

Candida albicans, a common fungal pathogen, uses a clever strategy to hide from the immune system by masking a molecule on its surface that would normally trigger an immune response. Researchers used both computer modeling and laboratory experiments to show that this hiding strategy involves two main processes: the fungus grows and exposes the molecule, while simultaneously using enzymes to shave it away. They found that a cellular signaling pathway called PKA is essential for activating these shaving enzymes in response to lactate, a signal from the host environment.

Background

Candida albicans is an opportunistic fungal pathogen that has evolved strategies to evade immune defenses by masking the proinflammatory pathogen-associated molecular pattern β-1,3-glucan. Most β-1,3-glucan lies in the inner cell wall shielded by an outer mannan layer, but some becomes exposed at the cell surface where it can be recognized by immune cells.

Objective

To elucidate how β-1,3-glucan masking dynamics in C. albicans are controlled by combining mathematical modeling with experimentation, focusing on the relative contributions of growth, β-1,3-glucan exposure, and enzymatic shaving to lactate-induced masking.

Results

The mathematical model accurately simulated β-1,3-glucan exposure dynamics and revealed that both growth rate and enzymatic shaving contribute to masking phenotypes. Gpr1/Gpa2-PKA signaling was confirmed as essential for lactate-induced β-1,3-glucan shaving, and Eng1 and Xog1 glucanases contribute to but are not essential for this shaving.

Conclusion

β-1,3-glucan masking results from dynamic interplay between growth-induced β-1,3-glucan exposure and PKA-dependent enzymatic shaving. This immune evasion strategy appears conserved among fungal pathogens and represents a form of adaptive prediction that enhances C. albicans fitness in host niches.
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