Intensive Exercise Does Not Preferentially Mobilize Skin-Homing T Cells and NK Cells

Intra-apheresis Cycling to Improve the Clinical Efficacy of Peripheral Blood Stem Cell Donations

Peripheral blood stem cell (PBSC) donation is the primary procedure used to collect haemopoietic stem cells (HSCs) for transplantation in individuals with haematological malignancies. More than 90,000 HSC transplants take place globally each year, and there is an increasing need to guarantee HSC mobilisation, improve tolerability to apheresis, and optimise immune reconstitution. Currently, mobilisation of HSCs depends upon pharmacological agents, with donors inactive during their subsequent apheresis. A successful yield of HSCs is not always achieved, and greater efficiency of collection procedures would improve the donors' safety and experience, along with the overall functioning of apheresis departments. The mobilisation of immune cells during bouts of exercise has been increasingly studied over the past 40 years. Exercise enriches peripheral blood with HSCs and immune cells such as cytolytic natural killer cells, and these may impact upon collection efficiency and patient outcomes following transplantation. Using exercise in conjunction with routine pharmaceutical agents may meet these needs. This article describes the impact of exercise on the quantity and engraftment potential of HSCs. Given that PBSC collections take on average 3-4 h per day per donor, and often consecutive days to complete, particular attention is paid to adopting interval exercise in this setting. Moreover, practical and safety considerations for allogeneic and autologous donors are discussed. 'Intra-apheresis cycling' is proposed as a feasible adjunctive strategy to evoke clinically significant improvements in the quality of the immune graft. Further research is needed to validate this concept in conjunction with routine mobilisation agents.

Brief cycling intervals incrementally increase the number of hematopoietic stem and progenitor cells in human peripheral blood

Introduction

Peripheral blood stem cell (PBSC) donation is the primary procedure used to collect hematopoietic stem and progenitor cells (HSPCs) for hematopoietic stem cell transplantation. Single bouts of exercise transiently enrich peripheral blood with HSPCs and cytolytic natural killer cells (CD56dim), which are important in preventing post-transplant complications. To provide a rationale to investigate the utility of exercise in a PBSC donation setting (≈3 h), this study aimed to establish whether interval cycling increased peripheral blood HSPC and CD56dim concentrations to a greater degree than continuous cycling.

Methods

In a randomised crossover study design, eleven males (mean ± SD: age 25 ± 7 years) undertook bouts of moderate intensity continuous exercise [MICE, 30 min, 65%-70% maximum heart rate (HRmax)], high-volume high intensity interval exercise (HV-HIIE, 4 × 4 min, 80%-85% HRmax) and low-volume HIIE (LV-HIIE, 4 × 2 min, 90%-95% HRmax). The cumulative impact of each interval on circulating HSPC (CD34+CD45dimSSClow) and CD56dim concentrations (cells/µL), and the bone marrow homing potential of HSPCs (expression of CXCR-4 and VLA-4) were determined.

Results

There was an increase in HSPC concentration after two intervals of LV-HIIE (Rest: 1.84 ± 1.55 vs. Interval 2: 2.94 ± 1.34, P = 0.01) and three intervals of HV-HIIE only (Rest: 2.05 ± 0.86 vs. Interval 3: 2.51 ± 1.05, P = 0.04). The concentration of all leukocyte subsets increased after each trial, with this greatest for CD56dim NK cells, and in HIIE vs. MICE (LV-HIIE: 4.77 ± 2.82, HV-HIIE: 4.65 ± 2.06, MICE: 2.44 ± 0.77, P < 0.0001). These patterns were observed for concentration, not frequency of CXCR-4+ and VLA-4+ HSPCs, which was unaltered. There was a marginal decrease in VLA-4, but not CXCR-4 expression on exercise-mobilised HSPCs after all trials (P < 0.0001).

Discussion

The results of the present study indicate that HIIE caused a more marked increase in HSPC and CD56dim NK cell concentrations than MICE, with mobilised HSPCs maintaining their bone marrow homing phenotype. LV-HIIE evoked an increase in HSPC concentration after just 2 × 2-minute intervals. The feasibility and clinical utility of interval cycling in a PBSC donation context should therefore be evaluated.

The effects of short-term, progressive exercise training on disease activity in smouldering multiple myeloma and monoclonal gammopathy of undetermined significance: a single-arm pilot study

BACKGROUND

High levels of physical activity are associated with reduced risk of the blood cancer multiple myeloma (MM). MM is preceded by the asymptomatic stages of monoclonal gammopathy of undetermined significance (MGUS) and smouldering multiple myeloma (SMM) which are clinically managed by watchful waiting. A case study (N = 1) of a former elite athlete aged 44 years previously indicated that a multi-modal exercise programme reversed SMM disease activity. To build from this prior case study, the present pilot study firstly examined if short-term exercise training was feasible and safe for a group of MGUS and SMM patients, and secondly investigated the effects on MGUS/SMM disease activity.

METHODS

In this single-arm pilot study, N = 20 participants diagnosed with MGUS or SMM were allocated to receive a 16-week progressive exercise programme. Primary outcome measures were feasibility and safety. Secondary outcomes were pre- to post-exercise training changes to blood biomarkers of MGUS and SMM disease activity- monoclonal (M)-protein and free light chains (FLC)- plus cardiorespiratory and functional fitness, body composition, quality of life, blood immunophenotype, and blood biomarkers of inflammation.

RESULTS

Fifteen (3 MGUS and 12 SMM) participants completed the exercise programme. Adherence was 91 ± 11%. Compliance was 75 ± 25% overall, with a notable decline in compliance at intensities > 70% V̇O2PEAK. There were no serious adverse events. There were no changes to M-protein (0.0 ± 1.0 g/L, P =.903), involved FLC (+ 1.8 ± 16.8 mg/L, P =.839), or FLC difference (+ 0.2 ± 15.6 mg/L, P =.946) from pre- to post-exercise training. There were pre- to post-exercise training improvements to diastolic blood pressure (- 3 ± 5 mmHg, P =.033), sit-to-stand test performance (+ 5 ± 5 repetitions, P =.002), and energy/fatigue scores (+ 10 ± 15%, P =.026). Other secondary outcomes were unchanged.

CONCLUSIONS

A 16-week progressive exercise programme was feasible and safe, but did not reverse MGUS/SMM disease activity, contrasting a prior case study showing that five years of exercise training reversed SMM in a 44-year-old former athlete. Longer exercise interventions should be explored in a group of MGUS/SMM patients, with measurements of disease biomarkers, along with rates of disease progression (i.e., MGUS/SMM to MM).

REGISTRATION

https://www.isrctn.com/ISRCTN65527208 (14/05/2018).

Harnessing the immunomodulatory effects of exercise to enhance the efficacy of monoclonal antibody therapies against B-cell haematological cancers: a narrative review

Therapeutic monoclonal antibodies (mAbs) are standard care for many B-cell haematological cancers. The modes of action for these mAbs include: induction of cancer cell lysis by activating Fcγ-receptors on innate immune cells; opsonising target cells for antibody-dependent cellular cytotoxicity or phagocytosis, and/or triggering the classical complement pathway; the simultaneous binding of cancer cells with T-cells to create an immune synapse and activate perforin-mediated T-cell cytotoxicity against cancer cells; blockade of immune checkpoints to facilitate T-cell cytotoxicity against immunogenic cancer cell clones; and direct delivery of cytotoxic agents via internalisation of mAbs by target cells. While treatment regimens comprising mAb therapy can lead to durable anti-cancer responses, disease relapse is common due to failure of mAb therapy to eradicate minimal residual disease. Factors that limit mAb efficacy include: suboptimal effector cell frequencies, overt immune exhaustion and/or immune anergy, and survival of diffusely spread tumour cells in different stromal niches. In this review, we discuss how immunomodulatory changes arising from exposure to structured bouts of acute exercise might improve mAb treatment efficacy by augmenting (i) antibody-dependent cellular cytotoxicity, (ii) antibody-dependent cellular phagocytosis, (iii) complement-dependent cytotoxicity, (iv) T-cell cytotoxicity, and (v) direct delivery of cytotoxic agents.

Potential Role of Chronic Physical Exercise as a Treatment in the Development of Vitiligo

Vitiligo is an autoimmune disease characterized by progressive skin depigmentation and the appearance of white patches throughout the body caused by significant apoptosis of epidermal melanocytes. Despite not causing any physical pain, vitiligo can originate several psychosocial disorders, drastically reducing patients' quality of life. Emerging evidence has shown that vitiligo is associated with several genetic polymorphisms related to auto-reactivity from the immune system to melanocytes. Melanocytes from vitiligo patients suffer from excess reactive oxygen species (ROS) produced by defective mitochondria besides a poor endogenous antioxidant system (EAS). This redox imbalance results in dramatic melanocyte oxidative stress (OS), causing significant damage in proteins, lipid membranes, and DNA. The damaged melanocytes secret damage-associated molecular pattern (DAMPs), inducing and increasing inflammatory gene expression response that ultimately leads to melanocytes apoptosis. Vitiligo severity has been also associated with increasing the prevalence and incidence of metabolic syndrome (MetS) or associated disorders such as insulin resistance and hypercholesterolemia. Thus, suggesting that in genetically predisposed individuals, the environmental context that triggers MetS (i.e., sedentary lifestyle) may also be an important trigger for the development and severity of vitiligo disease. This paper will discuss the relationship between the immune system and epidermal melanocytes and their interplay with the redox system. Based on state-of-the-art evidence from the vitiligo research, physical exercise (PE) immunology, and redox system literature, we will also propose chronic PE as a potential therapeutic strategy to treat and prevent vitiligo disease progression. We will present evidence that chronic PE can change the balance of inflammatory to an anti-inflammatory state, improve both EAS and the mitochondrial structure and function (resulting in the decrease of OS). Finally, we will highlight clinically relevant markers that can be analyzed in a new research avenue to test the potential applicability of chronic PE in vitiligo disease.

Comparison of the lymphocyte response to interval exercise versus continuous exercise in recreationally trained men

The purpose of this investigation was to compare changes in circulating lymphocyte subset cell counts between high-intensity interval exercise (HIIE), sprint interval exercise (SIE), and moderate-intensity continuous exercise (MICE). Recreationally active men (n ​= ​11; age: 23 ​± ​4 ​yr; height: 179.9 ​± ​4.5 ​cm; body mass: 79.8 ​± ​8.7 ​kg; body fat %:12.6 ​± ​3.8%; V̇O2max: 46.6 ​± ​3.9 ​ml⋅kg-1⋅min-1) completed a maximal graded exercise test to determine maximal oxygen uptake (V̇O2max) and three duration-matched cycling trials (HIIE, SIE, and MICE) in a randomized, counterbalanced fashion. HIIE consisted of fifteen 90-s bouts at 85% V̇O2max interspersed with 90-s active recovery periods. SIE consisted of fifteen 20-s bouts at 130% maximal power and 160-s active recovery periods. MICE was a continuous bout at 65% V̇O2max. Total exercise duration was 53 ​min in all three trials, including warm-up and cool-down. Blood was collected before, immediately post, 30 ​min, 2 ​h, 6 ​h, and 24 ​h post-exercise. Changes in lymphocyte subset counts, and surface expression of various markers were analyzed via flow cytometry. Changes were assessed using mixed model regression analysis with an autoregressive first order repeated measures correction. Significant decreases were observed in absolute counts of CD56dim NK cells, CD19+ B cells, CD4+ T cells, and CD8+ T cells 30 ​min and 24-h post-exercise in all three trials. Despite resulting in greater total work and oxygen consumption, MICE elicited similar changes in lymphocyte subset counts and receptor expression compared to both SIE and HIIE. Similarly, while the two interval trials resulted in differing oxygen consumption and total work, no differences in the lymphocyte response were observed. Though both forms of exercise resulted in declines in circulating lymphocyte cell counts, neither exercise type provides an immune-related advantage when matched for duration.

Acute and Chronic Effects of Interval Training on the Immune System: A Systematic Review with Meta-Analysis

Simple Summary

Interval training (IT) is a popular training strategy recognized by its positive effects on metabolic and cardiovascular system. However, there seems no consensus regarding the effects of IT on immune system parameters. Therefore, we aimed to summarize the evidence regarding the effects of IT on the immune system. As our many findings, an IT acutely promote a transitory change on immune cell count followed by reduced function. The magnitude of these changes seems to vary in accordance with IT type. On the other hand, the regular practice of IT might contribute to improve immune function without apparent change on immune cell count.

Abstract

Purpose: To summarize the evidence regarding the acute and chronic effects of interval training (IT) in the immune system through a systematic review with meta-analysis. Design: Systematic review with meta-analysis. Data source: English, Portuguese and Spanish languages search of the electronic databases Pubmed/Medline, Scopus, and SciELO. Eligibility criteria: Studies such as clinical trials, randomized cross-over trials and randomized clinical trials, investigating the acute and chronic effects of IT on the immune outcomes in humans. Results: Of the 175 studies retrieved, 35 were included in the qualitative analysis and 18 in a meta-analysis. Within-group analysis detected significant acute decrease after IT on immunoglobulin A (IgA) secretory rate (n = 115; MD = −15.46 µg·min⁻¹; 95%CI, −28.3 to 2.66; p = 0.02), total leucocyte count increase (n = 137; MD = 2.58 × 10³ µL⁻¹; 95%CI, 1.79 to 3.38; p < 0.001), increase in lymphocyte count immediately after exercise (n = 125; MD = 1.3 × 10³ µL⁻¹; 95%CI, 0.86 to 1.75; p < 0.001), and decrease during recovery (30 to 180 min post-exercise) (n = 125; MD = −0.36 × 10³ µL⁻¹;−0.57 to −0.15; p < 0.001). No effect was detected on absolute IgA (n = 127; MD = 47.5 µg·mL⁻¹; 95%CI, −10.6 to 105.6; p = 0.11). Overall, IT might acutely reduce leucocyte function. Regarding chronic effects IT improved immune function without change leucocyte count. Conclusion: IT might provide a transient disturbance on the immune system, followed by reduced immune function. However, regular IT performance induces favorable adaptations on immune function.

Systematic review on the effects of physical exercise on cellular immunosenescence-related markers - An update

Immunosenescence is a remodeling of the immune system occurring with aging that leads to an increased susceptibility to auto-immunity, infections and reduced vaccination response. A growing consensus supports the view that physical exercise may counteract immunosenescence and improve the immune response. Unfortunately, evidence regarding the effects of exercise on markers of cellular immunosenescence lacked uniformity at the time of an extensive literature review in 2016. Moreover, exercise-induced effects in older adults were underrepresented compared to young adults or completely lacking, such as for senescent T-cells and apoptosis of T-lymphocytes. The aim of this systematic literature study was to collect and appraise newly available data regarding exercise-induced changes on immunosenescence-related markers of immune cells and compare this against data that was already available in 2016. Systematic reviewing of newly available data in the field of exercise immunology provides additional evidence for the effect of exercise on immunosenescence-related cellular markers. Importantly, this review provides evidence for the effect of long-term exercise on senescent T-lymphocytes in older adults. Additionally, newly retrieved evidence shows an acute exercise-induced mobilization of naïve and memory cells in older adults. In general, data regarding long-term exercise-induced effects in older adults remain scarce. Noteworthy was the high number of articles describing exercise-induced effects on regulatory T-cells. However exercise-induced effects on this cell type are still inconclusive as some articles reported an exercise-induced up- or downregulation, while others reported no effects at all. Numerous studies on Natural Killer cell counts did not provide uniformity among data that was already available. Recent data regarding dendritic cells mostly described an increase after exercise. Overall, our literature update highlights the major influence of the type and intensity of exercise on immunosenescence-related markers, especially in older adults.

Regular Exercise May Restore Certain Age-Related Alterations of Adaptive Immunity and Rebalance Immune Regulation

Age-related changes of the immune system lead to an increased morbidity and mortality due to enhanced vulnerability to infectious diseases and malignancies. Recent studies revealed the important effects of physical activity on immune functions, which may largely depend on the type of exercise, its intensity and duration. However, limited information is available regarding the immunological effects of sport activities in older ages. The aim of our study was to examine the changes in a wide spectrum of lymphocyte subtypes after regular workout among healthy elderly individuals. We enrolled 29 elderly women with sedentary lifestyle (mean age: 67.03 ± 3.74 years) to take part in a 6-week long functional conditioning gymnastic exercise program. The percentages of peripheral natural killer (NK), NKT cells, T and B lymphocyte subtypes (early-/late-activated T, naïve and memory T, cytotoxic T (Tc), T-helper (Th)1, Th2, Th17, T regulatory type 1 (Tr1), CD4⁺CD127^lo/-CD25^bright Treg, as well as naïve and memory B cells) were determined by flow cytometry. Evaluation of the changes in functional capability of Treg cells was based on in vitro functional assays. At the end of exercise program, in parallel with improvements in body composition and physical performance, significant changes in naïve and memory lymphocyte ratios were observed. Importantly, levels of naïve Tc cells elevated, ratios of effector memory Tc cells decreased and distribution of memory B cells rearranged as well. Additionally, proportions of late-activated HLA-DR⁺ T cells increased, while percentages of anti-inflammatory interleukin (IL)-10 producing Tr1 cells, as well as immunosuppressive CD4⁺CD127^lo/-CD25^bright Treg cells decreased following the exercise workout. Changes observed after the regular exercise program indicate an improvement in the age-related redistribution of certain naïve and memory cell proportions and a retuned immune regulation in older ages.

High intensity interval exercise increases the frequency of peripheral PD-1+ CD8+ central memory T-cells and soluble PD-L1 in humans

Exercise can exert anti-inflammatory effects in an intensity-dependent manner; however, the mechanisms mediating these effects are continually being established. Programme Death Receptor-1 (PD-1) is a membrane bound receptor that maintains immune tolerance by dampening immune cell interactions, such as those mediated by cytotoxic T-cell lymphocytes (CD8⁺). The aim of this study was to characterise sub-populations of CD8⁺ T-cells with regards to their expression of PD-1 before and immediately after exercise. Interleukin (IL)-6, soluble PD-1 (sPD-1) and its ligand (sPD-L1) were also quantified in plasma. Eight individuals (mean ​± ​SD: age 29 ​± ​5 years; BMI 24.2 ​± ​3.4 ​kg ​m²; V˙O_2max 44.5 ​± ​6.4 ​ml ​kg⁻¹·min⁻¹) undertook two time and energy-matched cycling bouts in a counterbalanced study design: one of moderate intensity (MOD) and a bout of high intensity interval exercise (HIIE). Both MOD and HIIE increased the number, but not the proportion of circulating CD8⁺ PD-1+ cells, with no differences between trials. Within the CD8⁺ PD-1+ pool, the expression of PD-1 increased on central memory cells following HIIE only (fold change: MOD 1.0 vs HIIE +1.4), as well the concentration of CD8+PD-1+ memory cells within the circulation (cells/uL: MOD -0.4 vs HIIE +5.8). This response composed a very small part of the exercise-induced CD8⁺ lymphocytosis (Pre-Ex: 0.38% to Post-Ex: 0.69%; p ​> ​0.05). sPD-L1 and IL-6 concentration increased in tandem following MOD and HIIE (r ​= ​0.57; P ​= ​0.021), with a reciprocal decline in sPD-1 observed. The current data demonstrate that PD-1+ CD8⁺ lymphocytes were mobilised following both MOD and HIIE. Both the number of central memory CD8⁺ T-cells expressing PD-1 and the expression level on these cells were increased following HIIE only. This intensity-dependent phenotypic response, in conjunction with increased circulatory sPD-L1 may represent an aspect of the anti-inflammatory response to exercise and warrants further investigation.

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PD-1 is a membrane-bound T-cell receptor that regulates immune tolerance.

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We explored phenotypic changes in PD-1+ T-cells after exercise.

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Circulating PD-1+ CD8⁺ T-cells increased after moderate and high intensity interval exercise (HIIE).

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Central memory CD8⁺ T-cell number and expression increased after HIIE only.

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Post-exercise levels of soluble PD-1 Ligand increased and correlated with IL-6.

Gender Differences in Chronic Hormonal and Immunological Responses to CrossFit®

This study was designed to analyze the chronical responses of the hormonal and immune systems after a CrossFit^® training period of six months as well as to compare these results between genders. Twenty-nine CrossFit^® practitioners (35.3 ± 10.4 years, 175.0 ± 9.2 cm, 79.5 ± 16.4 kg) with a minimum CrossFit^® experience of six months were recruited, and hormonal and immune responses were verified every two months during training. The training was conducted in five consecutive days during the week, followed by two resting days. Testosterone (T) values were significantly higher at the last measurement time (T6 = 346.0 ± 299.7 pg·mL^-1) than at all the other times (p < 0.002) and were higher in men than in women (p < 0.001). Cortisol (C) levels were lower at all times compared to the initial level before training, and differences were observed between men and women, with men having a lower value (T0: p = 0.028; T2: p = 0.013; T4: p = 0.002; and T6: p = 0.002). The TC ratio in women was lower at all times (p < 0.0001) than in men. Significant effects on CD8 levels at different times (F_(3.81) = 7.287; p = 0.002; η_p² = 0.213) and between genders (F_(1.27) = 4.282; p = 0.048; η_p² = 0.137), and no differences in CD4 levels were observed. CrossFit^® training changed the serum and basal levels of testosterone and cortisol in men (with an increase in testosterone and a decrease in cortisol).

T lymphocyte phenotype of contact-allergic patients: experience with nickel and p-phenylenediamine

BACKGROUND

There is considerable interest in understanding the immunological variables that have the greatest influence on the effectiveness of sensitization by contact allergens, particularly in the context of developing new paradigms for risk assessment of novel compounds.

OBJECTIVES

To examine the relationship between patch test score for three different contact allergens and the characteristics of T cell responses.

METHODS

A total of 192 patients with confirmed nickel, p-phenylenediamine (PPD) or methylisothiazolinone (MI) allergy were recruited from the Contact Dermatitis Investigation Unit at Salford Royal Hospital. Severity of allergy was scored by the use of patch testing, peripheral blood lymphocytes were characterized for T cell phenotype by flow cytometry, and proliferative activity was characterized by radiolabelled thymidine incorporation. Comparisons were drawn with buffy coat samples from healthy volunteers.

RESULTS

Patch test positivity for nickel, PPD and MI was associated with changes in the phenotype of peripheral blood T cells: increases in naïve cells, decreases in regulatory T cell frequency and the CD4+ /CD8hi ratio, and increased expression of the skin-homing marker cutaneous lymphocyte antigen (CLA), particularly for those patients with a +++ patch test score.

CONCLUSIONS

This increased understanding of the characteristics of the T cell responses to contact allergens may provide parameters with which to better measure health risks associated with skin sensitization.

Acute aerobic exercise induces a preferential mobilisation of plasmacytoid dendritic cells into the peripheral blood in man

Dendritic cells (DCs) are important sentinel cells of the immune system responsible for presenting antigen to T cells. Exercise is known to cause an acute and transient increase in the frequency of DCs in the bloodstream in humans, yet there are contradictory findings in the literature regarding the phenotypic composition of DCs mobilised during exercise, which may have implications for immune regulation and health. Accordingly, we sought to investigate the composition of DC sub-populations mobilised in response to acute aerobic exercise. Nine healthy males (age, 21.9 ± 3.6 years; height, 177.8 ± 5.4 cm; body mass, 78.9 ± 10.8 kg; body mass index, 24.9 ± 3.3 kg·m²; V̇O_{2 MAX}, 41.5 ± 5.1 mL·kg·min^-1) cycled for 20 min at 80% V̇O_{2 MAX}. Blood was sampled at baseline, during the final minute of exercise and 30 min later. Using flow cytometry, total DCs were defined as Lineage- (CD3, CD19, CD20, CD14, CD56) HLA-DR+ and subsequently identified as plasmacytoid DCs (CD303+) and myeloid DCs (CD303-). Myeloid DCs were analysed for expression of CD1c and CD141 to yield four sub-populations; CD1c-CD141+; CD1c+CD141+; CD1c+CD141- and CD1c-CD141-. Expression of CD205 was also analysed on all DC sub-populations to identify DCs capable of recognising apoptotic and necrotic cells. Total DCs increased by 150% during exercise (F_(1,10) = 60; p < 0.05, η² = 0.9). Plasmacytoid DCs mobilised to a greater magnitude than myeloid DCs (195 ± 131% vs. 131 ± 100%; p < 0.05). Among myeloid DCs, CD1c-CD141- cells showed the largest exercise-induced mobilisation (167 ± 122%), with a stepwise pattern observed among the remaining sub-populations: CD1c+CD141- (79 ± 50%), followed by CD1c+CD141+ (44 ± 41%), with the smallest response shown by CD1c-CD141+ cells (23 ± 54%) (p < 0.05). Among myeloid DCs, CD205- cells were the most exercise responsive. All DC subsets returned to resting levels within 30 min of exercise cessation. These results show that there is a preferential mobilisation of plasmacytoid DCs during exercise. Given the functional repertoire of plasmacytoid DCs, which includes the production of interferons against viral and bacterial pathogens, these findings indicate that exercise may augment immune-surveillance by preferentially mobilising effector cells; these findings have general implications for the promotion of exercise for health, and specifically for the optimisation of DC harvest for cancer immunotherapy.

Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan

Epidemiological evidence indicates that regular physical activity and/or frequent structured exercise reduces the incidence of many chronic diseases in older age, including communicable diseases such as viral and bacterial infections, as well as non-communicable diseases such as cancer and chronic inflammatory disorders. Despite the apparent health benefits achieved by leading an active lifestyle, which imply that regular physical activity and frequent exercise enhance immune competency and regulation, the effect of a single bout of exercise on immune function remains a controversial topic. Indeed, to this day, it is perceived by many that a vigorous bout of exercise can temporarily suppress immune function. In the first part of this review, we deconstruct the key pillars which lay the foundation to this theory-referred to as the "open window" hypothesis-and highlight that: (i) limited reliable evidence exists to support the claim that vigorous exercise heightens risk of opportunistic infections; (ii) purported changes to mucosal immunity, namely salivary IgA levels, after exercise do not signpost a period of immune suppression; and (iii) the dramatic reductions to lymphocyte numbers and function 1-2 h after exercise reflects a transient and time-dependent redistribution of immune cells to peripheral tissues, resulting in a heightened state of immune surveillance and immune regulation, as opposed to immune suppression. In the second part of this review, we provide evidence that frequent exercise enhances-rather than suppresses-immune competency, and highlight key findings from human vaccination studies which show heightened responses to bacterial and viral antigens following bouts of exercise. Finally, in the third part of this review, we highlight that regular physical activity and frequent exercise might limit or delay aging of the immune system, providing further evidence that exercise is beneficial for immunological health. In summary, the over-arching aim of this review is to rebalance opinion over the perceived relationships between exercise and immune function. We emphasize that it is a misconception to label any form of acute exercise as immunosuppressive, and, instead, exercise most likely improves immune competency across the lifespan.

T-cells and their cytokine production: The anti-inflammatory and immunosuppressive effects of strenuous exercise

Strenuous exercise bouts and heavy training are associated with a heightened anti-inflammatory state and a transient suppression of several immune components. In turn, many athletes are susceptible to illness, particularly upper respiratory symptoms (e.g. cough, sore throat, running nose). T-lymphocytes (T-cells) are important for orchestrating the immune response and can be categorised into subsets according to their phenotypical characteristics resulting from polarisation (i.e. type-1, type-2 and regulatory T-cells). Each T-cell subset has a unique functional role, including their capacity to produce pro- and anti-inflammatory cytokines in response to an immune challenge. Prolonged and exhaustive exercise typically reduces peripheral blood type-1 T-cell number and their capacity to produce the pro-inflammatory cytokine, interferon-γ. Moreover, heavy training loads are associated with elevated numbers of resting peripheral blood type-2 and regulatory T-cells, which characteristically produce the anti-inflammatory cytokines, interleukin-4 and interleukin-10, respectively. This appears to increase the risk of upper respiratory symptoms, potentially due to the cross-regulatory effect of interleukin-4 on interferon-γ production and immunosuppressive action of IL-10. Catecholamines significantly influence the number of peripheral blood T-cells in response to exercise. Whereas, glucocorticoids and prostaglandin E2 promote the production of anti-inflammatory cytokines by T-cells. In summary, strenuous exercise bouts and heavy training shifts T-cell immunity towards an anti-inflammatory state. This impairs the ability of the immune system to mount an inflammatory response to an immune challenge, which may weaken defences against intracellular pathogens (e.g. viruses), and increase the risk of infection and viral reactivation.

Recovery of the immune system after exercise

The notion that prolonged, intense exercise causes an "open window" of immunodepression during recovery after exercise is well accepted. Repeated exercise bouts or intensified training without sufficient recovery may increase the risk of illness. However, except for salivary IgA, clear and consistent markers of this immunodepression remain elusive. Exercise increases circulating neutrophil and monocyte counts and reduces circulating lymphocyte count during recovery. This lymphopenia results from preferential egress of lymphocyte subtypes with potent effector functions [e.g., natural killer (NK) cells, γδ T cells, and CD8⁺ T cells]. These lymphocytes most likely translocate to peripheral sites of potential antigen encounter (e.g., lungs and gut). This redeployment of effector lymphocytes is an integral part of the physiological stress response to exercise. Current knowledge about changes in immune function during recovery from exercise is derived from assessment at the cell population level of isolated cells ex vivo or in blood. This assessment can be biased by large changes in the distribution of immune cells between blood and peripheral tissues during and after exercise. Some evidence suggests that reduced immune cell function in vitro may coincide with changes in vivo and rates of illness after exercise, but more work is required to substantiate this notion. Among the various nutritional strategies and physical therapies that athletes use to recover from exercise, carbohydrate supplementation is the most effective for minimizing immune disturbances during exercise recovery. Sleep is an important aspect of recovery, but more research is needed to determine how sleep disruption influences the immune system of athletes.

Exercise-induced B cell mobilisation: Preliminary evidence for an influx of immature cells into the bloodstream

The number of peripheral blood B lymphocytes doubles during acute exercise, but the phenotypic composition of this response remains unknown. In two independent exercise studies, using complimentary phenotyping strategies, we investigated the mobilisation patterns of distinct B cell subsets. In study one, nine healthy males (mean±SD age: 22.1±3.4years) completed a continuous cycling bout at 80% V̇O2MAX for 20min. In study two, seven healthy experienced cyclists (mean±SD age: 29.9±4.7years) completed a 30min cycling trial at a workload corresponding to +5% of the individual blood lactate threshold. In study one, CD3-CD19+ B cell subsets were classified into immature (CD27-CD10+), naïve (CD27-CD10-), memory (CD27+CD38-), plasma cells/plasmablasts (CD27+CD38+) and finally, recently purported 'B1' cells (CD27+ CD43+ CD69-). In study two, CD20+ B cells were classified into immature (CD27-IgD-), naïve (CD27-IgD+), and IgM+/IgG+/IgA+ memory cells (CD27+IgD-). Total B cells exhibited a mean increase of 88% (study one) and 60% (study two) during exercise. In both studies, immature cells displayed the greatest increase, followed by memory cells, then naïve cells (study one: immature 130%>mature 105%>naïve 84%; study two: immature 110%>mature 56%>naïve 38%). Our findings show that, unlike T cells and NK cells, B cell mobilisation is not driven by effector status, and, for the first time, that B cell mobilisation during exercise is comprised of immature CD27- IgD-/CD10+ cells.