*Maurer and Barletta equal first author contribution.
Coronavirus disease 19 (COVID-19) is an infectious disease transmitted mainly through aerosol spread of severe acute respiratory syndrome coronavirus-2 (SARSCoV-2) and in most cases leads mild to moderate respiratory illness, which usually resolves within 5-7 days. Regular moderate-to-vigorous exercise has been associated with a strong and timely immune response against infections, thus reducing susceptibility to acute respiratory illness, and also protecting from severe COVID-19 outcomes. Frequent high intensity training has also been proposed to enhance vaccine-induced cellular and humoral immunity. However, long-term high-intensity physical activity and stressors associated with elite sports might cause hyperinflammation in some individuals and increase the risk of respiratory illness, and ice hockey players are among those winter sport athletes, who have the highest incidence in that context. Proteomic profiling of COVID-19 patients has proven valuable in the discovery of novel biomarkers associated with disease susceptibility, course, complications and severity, but so far there are no reports of COVID-19 proteomic studies in athletes. Herein, we examined the immune-inflammatory proteome of elite ice hockey players before and after a team-wide COVID-19 outbreak with the omicron BA.1 variant in December 2021.
Serum blood samples and questionnaire data were obtained from 24 players of a Swiss National League ice hockey team 3 months prior to COVID-19 and from the same players within 1-2 weeks after nasal swab PCR-confirmed SARS-CoV-2 infection, and of 20 controls, that are non-ice hockey players after recent recovery from COVID-19. Proximity extension assay (PEA) technology by OLINK was used for targeted proteomic serum analyses of 180 proteins measured in the OLINK immune response and inflammation panels (92 proteins each, 4 overlaps).
Immune-inflammatory profiles of ice hockey players were compared at two time points (pre- and post-COVID-19). Additionally, post-COVID-19 profiles of ice hockey players were compared to the post-COVID-19 control group for reference. Ice hockey players and control subjects reported comparable rates of previous SARSCoV-2 infections, atopic comorbidities (asthma, allergic rhinitis), regularly occurring upper respiratory tract infections (URTI), fever and recurrent herpes labialis. COVID-19 vaccination history did not differ between athletes and controls. Control subjects reported a higher prevalence of symptoms in general, and respiratory symptoms specifically. Clinical laboratory serum analyses showed no difference between ice hockey players and controls. PEA-based proteomic analyses of serum samples from elite ice hockey players identified 28 differentially expressed proteins involved in immune response and inflammation with a rather distinct representation of biological process networks. While similar process networks were found to be present at both sampling time points, specifically, lymphocyte proliferation (CXCL12, CD40, PRKCQ, TNFSF14pre-COVID19 and TRAF2, IRAK4, CASP-8 post-COVID-19) and innate inflammatory response (PRKCQ, IRAK1 pre-COVID-19 and of TRAF2, IRAK4 post-COVID-19), the post-COVID-19 profile was uniquely marked by an increase in proteins involved in innate immune response to viral infection, neutrophil activation, IL-12/-15/- 18 and IFNγ-signaling. This last finding therefore may reflect how the immune system responds efficiently to COVID-19, where a timely release of antiviral interferons seems to be essential. While we could clearly separate athletes pre- and post-infection, post-COVID-19 comparison of ice hockey players with post-COVID-19 samples of the control non-ice hockey players group revealed similar proteomic patterns, with only CCL11 showing a significantly higher expression in the control group. Of note, levels of CCL11 have recently been found to be elevated in patients experiencing cognitive symptoms (”brain fog”) after mild COVID-19 compared to those without such symptoms. 6 However, we did not assess incidence of post- or long-COVID-19 symptoms in our cohorts. It could be hypothesized that the higher reported incidence of COVID-19 symptoms in the control group might be linked with a weaker immunological response to either the virus, the vaccination or both, or even due to the fact that more ice hockey players had received a booster shot by the time they got infected (33% vs. 15% of controls).
To conclude, we found that immune-inflammatory proteomic profiles in serum of elite ice hockey players differ significantly pre- and post-COVID-19. The cause for this observation might be multifactorial, e.g., direct impact of the recent SARS-CoV-2 infection, seasonal changes, or training-related influences on sampling timepoints. Although proteomic profiles generally did not differ between athletes and control subjects post-COVID-19, the higher incidence of symptomatic disease in the control group warrants follow-up studies to investigate the potential impact of athletic workloads on (SARS-CoV-2) infection susceptibility, disease course and vaccination response, as well as to identify associated biomarkers.