Peak V̇O₂, not resting spleen volume predicts cellular immune marker mobilization after aerobic exercise

This study aimed to examine white blood cell and platelet mobilization after moderate-intensity aerobic exercise, its association with spleen volume, and the potential mediating role of peak V̇O₂.

Twenty participants (24 ± 4 years-old) completed all study procedures, including a detailed medical examination, supine cardio-pulmonary exercise test (CPET) and three step-transitions from 20 W to a moderate-intensity power output, equivalent to V̇O₂ uptake at 90 % gas exchange threshold. During these step-transitions cardiometabolic and splenic responses were simultaneously measured. Blood samples were collected before and immediately after moderate-intensity cycling.

In response to aerobic exercise, the spleen volume was significantly reduced (by 83 ± 39 mL, p = 0.001), while the increase in systemic immune inflammation index (SII), neutrophil-lymphocyte-ratio (NLR) and serum TNF-α protein concentration were not significant. A significant decrease of -7 % (p = 0.049, ⅾ=0.48) was observed for platelet-lymphocyte-ratio (PLR). A multiple regression analysis revealed that a higher peak V̇O₂ (p = 0.031), but not resting spleen volume (p = 0.614), predicted the post-exercise increase in PLR (p = 0.049), explaining 25 % of the common variance. Changes in NLR (p = 0.423), SII (p = 0.198) or TNF-α (p = 0.808) were not associated with peak V̇O₂ or resting spleen volume.

Apparently, greater cardiorespiratory fitness, rather than resting spleen volume, modulates specific and transient changes of some circulating immune markers following moderate-intensity cycling.