**1. Introduction**

Studies of the last decades on the role of a sedentary lifestyle in developing chronic diseases have highlighted the critical importance of regular physical activity and exercise in maintaining health and reducing risk of several disorders. Lower physical activity levels correlate with the development of many chronic diseases and unhealthy conditions, such as obesity, hypertension, cardiovascular diseases, type 2 diabetes mellitus, metabolic syndrome and other chronic inflammatory disorders [1,2], while regular physical activity and exercise have beneficial effects in these conditions [3]. Growing evidence also underlines the preventive role of a physically active lifestyle in infections and other immune-mediated diseases by improving immune competency and regulation [4–6]. However, the immunological effects of exercise and its interpretation are still controversial in some cases. It is well known that a single bout of exercise is associated with an initial enhancement in peripheral lymphocyte numbers and effector immune functions, quickly followed by a brief period of immune depression that can last 3–72 h after the exercise bout [7]. The decrease in lymphocyte levels following the exercise has been partially explained by an increase in apoptosis [8]. It was reported that prolonged exercise decreases Th1 cell levels, but not Th2 cells [9], which selectivity could be explained by the increase of stress hormone levels

**Citation:** Balogh, L.; Szabó, K.; Pucsok, J.M.; Jámbor, I.; Gyetvai, Á.; Mile, M.; Barna, L.; Szodoray, P.; Tarr, T.; Csiki, Z.; et al. The Effect of Aerobic Exercise and Low-Impact Pilates Workout on the Adaptive Immune System. *J. Clin. Med.* **2022**, *11*, 6814. https://doi.org/ 10.3390/jcm11226814

Academic Editor: David Rodríguez-Sanz

Received: 13 October 2022 Accepted: 14 November 2022 Published: 17 November 2022

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(e.g., cortisol, catecholamines) and myokines in the peripheral blood [10]. Of note, cortisol suppresses the production of interleukin (IL)-12 of antigen-presenting cells (APC), which is a well-known stimulator of Th1 and NK cells [11]. These observations led to the creation of the so-called 'open window' hypothesis, which assumed that the immune system is transiently compromised after acute exercise. However, observations in animal models revealed that T cells are redeployed to the gut, lungs, and bone marrow following exercise [12]. This contributed to the development of a more up-to-date viewpoint in interpreting decreased immune cell frequencies after exercise, which might reflect the even heightened immune-surveillance and immuno-regulatory activities instead of the suppression of the immune system [13,14].

Regarding the long-lasting effects of excessive high-intensity and high-volume physical activity typically practiced by highly competitive athletes, a reduction in proportions of immunocompetent cells with effector functions and decrease of several cytokines, including IL-6, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-1β, IL-2, IL-8 and IL-10, were reported [15,16]. Save for the frequent and arduous bouts of exercise that far exceed recommended physical activity guidelines, there is no doubt that an active lifestyle with regular exercise results in improved immune functions and reduction of systemic inflammatory activity. Former observations reported increased IL-2 production, T-cell proliferation, NK cell cytotoxic activity and enhanced vaccine responses [17,18]. Furthermore, it has also been suggested that repeated bouts of exercise may delay immunosenescence by limiting the accumulation of memory T cell subsets and increasing the frequency of circulating naive T cells [19].

Low-impact workouts, such as Pilates, are beneficial to individuals who cannot perform intensive or moderate-intensity exercises due to chronic health conditions. The purpose of the movements is to increase core strength and muscle balance, improve flexibility and posture; meanwhile, practicing effective breathing exercises during Pilates can encourage relaxation and reduce stress [20]. Although we have a rapidly expanding knowledge on the immunological effects of high- and moderate-intensity workouts, there is still only limited information available about the effects of low-impact exercises, especially on the level of the adaptive immune system. Therefore, our study aimed to examine and compare the changes in a broad spectrum of lymphocyte subtypes after aerobic-type total-body shaping and low-impact Pilates workouts among healthy individuals.
