BACKGROUND

Regular exercise, particularly moderate-intensity continuous training (MICT), can improve immune function. Natural killer (NK) cells, a subset of lymphocytes that react to infections, are the most responsive innate immune cells to exercise, but the mechanisms underlying this are poorly understood. A type of exercise training that is gaining popularity in recent years is high-intensity interval training (HIIT), but how it affects NK cells is largely unknown. In fact, intense exercise has been traditionally viewed as a potential stressor to immune homeostasis. The purpose of this study was to determine in healthy, previously untrained adults (N=8 [3 male; 40±6 years]) the effects of an intervention consisting of 4-week MICT followed by 4-week HIIT on NK cells as compared with a pre-training (baseline) state.

METHODS

Participants were studied at three time points: baseline, mid-intervention (after MICT), and post-intervention (after HIIT). Main assessments included cytotoxicity assays, flow-cytometry analysis of NK cell surface markers, and interrogation of the cellular proteome using a systems biology approach.

RESULTS

A significant time effect was found for NK cell cytotoxicity (p<0.001), which was increased ~10-fold at both midand post-intervention versus baseline. No significant intervention effect was found for NK surface receptor expression, except for CXCR3 determined as mean fluorescence intensity (p=0.044, although with no significant differences in post hoc pairwise comparisons). The proteins showing a higher differential expression (Log2 fold-change > 10 and false discovery rate [FDR] q-value < 0.001) were COP9 signalosome subunit 3 (COPS3), DnaJ heat shock protein family member B11 (DNAJB11), histidyl-TRNA synthetase 1 (HARS), NIMA related kinase 9 (NEK9), nucleoporin 88 (NUP88), phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), regulator of chromosome condensation 2 (RCC2), TAO kinase 3 (TAOK3), transducin beta like 2 (TBL2), and ring finger protein 40 (RNF40). All were upregulated at mid-intervention compared with baseline, with the exception of HARS, which was downregulated. Four enriched pathways (FDR p<25%) were found: two related to transmembrane transport and cellular composition (downregulated at mid-intervention vs baseline), and two related to oxidation- reduction reactions (regulated at post-intervention versus baseline).

CONCLUSION

A progressive exercise intervention of MICT followed by HIIT induces a remarkable improvement in NK function compared with the untrained state, although at the mechanistic level the pathways involved seem to differ over time during the intervention.