Lymphocyte and dendritic cell response to a period of intensified training in young healthy humans and rodents: A systematic review and meta-analysis

Abstract

Background: Intensified training coupled with sufficient recovery is required to improve athletic performance. A stress-recovery imbalance can lead to negative states of overtraining. Hormonal alterations associated with intensified training, such as blunted cortisol, may impair the immune response. Cortisol promotes the maturation and migration of dendritic cells which subsequently stimulate the T cell response. However, there are currently no clear reliable biomarkers to highlight the overtraining syndrome. This systematic review and meta-analysis examined the effect of intensified training on immune cells. Outcomes from this could provide insight into whether these markers may be used as an indicator of negative states of overtraining.Methods: SPORTDiscus, PUBMED, Academic Search Complete, Scopus and Web of Science were searched until June 2022. Included articles reported on immune biomarkers relating to lymphocytes, dendritic cells, and cytokines before and after a period of intensified training, in humans and rodents, at rest and in response to exercise.Results: 164 full texts were screened for eligibility. Across 57 eligible studies, 16 immune biomarkers were assessed. 7 were assessed at rest and in response to a bout of exercise, and 9 assessed at rest only. Included lymphocyte markers were CD3+, CD4+ and CD8+ T cell count, NK cell count, NK Cytolytic activity, lymphocyte proliferation and CD4/CD8 ratio. Dendritic cell markers examined were CD80, CD86, and MHC II expression. Cytokines included IL-1β, IL-2, IL-10, TNF-α and IFN-γ. A period of intensified training significantly decreased resting total lymphocyte (d= −0.57, 95% CI −0.30) and CD8+ T cell counts (d= −0.37, 95% CI −0.04), and unstimulated plasma IL-1β levels (d= −0.63, 95% CI −0.17). Resting dendritic cell CD86 expression significantly increased (d = 2.18, 95% CI 4.07). All other biomarkers remained unchanged.Conclusion: Although some biomarkers alter after a period of intensified training, definitive immune biomarkers are limited. Specifically, due to low study numbers, further investigation into the dendritic cell response in human models is required.

Immunomodulatory effects of exercise in cancer prevention and adjuvant therapy: a narrative review

“…A study on human exercise showed that physical activity results in the enhancement of peripheral blood DCs ( LaVoy et al, 2015a ). Furthermore, physical activity results in the upregulation of DC-associated IL-12 and MHC II expression in animal models ( Baker et al, 2022 ). A study investigating the mobilized DC subpopulation composition owing to acute aerobic physical activity found that plasmacytoid DCs are preferentially mobilized into peripheral circulation following exercise, which results in improved immune surveillance ( Brown et al, 2018 ).…”

The Impact of Inadequate Sleep on Overtraining Syndrome in Male and Female College Athletes 18–22 Years Old: A Literature Review

“…It is important to consider that the immune system is complex, and intense training sensations and elevated levels of cortisol influence immune markers in diverse ways. Therefore, the variations can alter in everyone, and thus it is important to consider multiple diagnostic markers [11].…”

A Narrative Review on Adipose Tissue and Overtraining: Shedding Light on the Interplay among Adipokines, Exercise and Overtraining

“…On the other hand, exercise and training induce changes in circulating numbers of lymphocyte subsets [66]. With heavy training, the T-lymphocyte CD4+/CD8+ ratio typically decreases [67]. However, this ratio seems to be similar between athletes diagnosed with OTS and well-trained athletes [68].…”