The study examined the effect of exercise and hypoxia on the mobilization and egress of innate lymphocytes (ILCs) and adaptive T cell populations in the blood. The ILCs have emerged as a critical population of cells in immune regulation at mucosal surfaces in animals and humans. Eleven healthy male subjects performed (i) 45 min of exercise at 50% VO2 peak on a cycle ergometer under normoxia and (ii) hypoxia, or (iii) while resting in hypoxia. Blood samples were obtained pre-exercise, immediately post-exercise and 60 min post-exercise and were analyzed by flow cytometry to examine the type 1 and type 3 ILCs and CD4+ and CD8+ naive and memory cell populations. There was a significant increase in the number of type 1 (NK cells) and type 3 ILC22 cells in the blood in response to exercise under normal oxygen conditions followed by a significant egress of these cells following the cessation of exercise. Exercise performed under hypoxic conditions abrogated the mobilization response of NK cells and ILC22 cells. Type 3 LTi cells were mobilized into the blood only under hypoxic rest conditions. No significant changes were observed when we analysed total CD4+ and CD8+T cell populations or the naive and memory subsets. This study highlights that distinct innate populations are mobilised under different environmental conditions and types of stress.


hypoxemia, normoxia, inflammation, innate, lymphocytes, cycling