Blood levels of antimicrobial peptides hBD-2 and S100A8/A9 surged after marathon and half-marathon running, and S100A8 levels correlated with reduced lung function — suggesting these peptides could serve as biomarkers for exercise-induced respiratory stress.
S100A8 negatively correlated with lung functionHigher blood levels of the antimicrobial peptide S100A8 were associated with lower forced expiratory volume and mid-expiratory flows in runners, linking this immune peptide to airway dysfunction
What the researchers found
Serum levels of hBD-2 and S100A8/A9 were significantly elevated immediately after the race in both marathon and half-marathon runners compared to baseline and sedentary controls, then returned to baseline by seven days postrace.
In runners who developed exercise-induced bronchoconstriction (EIB), S100A8 levels remained slightly elevated during recovery, and hBD-2 was modestly increased. Critically, S100A8 levels showed a negative correlation with lung function parameters including forced expiratory volume and mid-expiratory flows — meaning higher peptide levels were associated with worse airway function. Angiogenin and major basic protein (MBP) did not show the same pattern.
Why it matters
Exercise-induced bronchoconstriction affects up to 50% of elite endurance athletes and can impair performance and health. Currently, there are no simple blood-based biomarkers to predict which athletes are at risk. If antimicrobial peptides like S100A8 can identify susceptible individuals before symptoms develop, it could enable personalized prevention strategies — such as modified training regimens, pre-treatment protocols, or environmental controls — to protect athletes' airway health during intense endurance competition.
How the study worked
A prospective study enrolled 34 marathon runners and 36 half-marathon runners, with 30 sedentary controls. Blood samples were collected at three time points: baseline (before the race), immediately postrace, and seven days postrace. Serum concentrations of five antimicrobial peptides (angiogenin, hBD-2, MBP, S100A8, and S100A8/A9) were measured using ELISA. Lung function was assessed by spirometry at each time point to identify exercise-induced bronchoconstriction.
What this study cannot tell us
The study had a moderate sample size (70 runners, 30 controls) and was conducted in the context of a single race event, limiting generalizability to other endurance activities. The correlation between S100A8 and lung function, while statistically significant, was modest in magnitude. The study measured circulating peptide levels but did not assess local airway concentrations, which may differ. It cannot establish whether elevated peptides cause airway dysfunction or are simply markers of it. Individual variability in training status, race conditions, and pre-existing respiratory conditions may confound results.
How to read the evidence
This is a prospective observational study with appropriate controls and multiple time points. The design is well-structured for an exploratory biomarker study, but the modest sample size and single-event context limit the strength of conclusions. The correlation between S100A8 and lung function requires validation in larger cohorts.
When this study was published
Published in 2025, this is a very recent study reflecting current interest in immune biomarkers for personalized sports medicine.
The bigger picture
This study sits at the intersection of exercise immunology and antimicrobial peptide research. While antimicrobial peptides are best known for fighting infections, they also function as damage signals and immune modulators. The finding that intense exercise triggers their systemic release adds to the growing understanding that antimicrobial peptides participate in sterile inflammation — immune responses triggered by physical stress rather than pathogens. This has implications beyond sports medicine, as similar peptide-mediated inflammatory responses may occur in occupational settings, military training, and other high-physical-demand scenarios.
Questions still open
- Could pre-race antimicrobial peptide levels predict which runners will develop exercise-induced bronchoconstriction, enabling preventive intervention?
- Are the elevated peptide levels driving the airway inflammation, or are they a downstream marker of tissue stress?
- Do these peptide responses differ with training status — would highly trained athletes show a blunted or exaggerated response compared to recreational runners?
Common questions
What happens to the immune system during a marathon?
Could these peptide biomarkers help prevent breathing problems in runners?
Read the original research
Circulating Antimicrobial Peptides as Biomarkers of Inflammation and Airway Dysfunction After Marathon Running.
Biology, 14(7)
Citation
Lingitz, Marie-Therese; Kühtreiber, Hannes; Auer, Lisa; Mildner, Michael; Krenn, Claus G; Aigner, Clemens; Moser, Bernhard; Bekos, Christine; Ankersmit, Hendrik Jan. (2025). Circulating Antimicrobial Peptides as Biomarkers of Inflammation and Airway Dysfunction After Marathon Running.. Biology, 14(7). https://doi.org/10.3390/biology14070825