Apoptosis does not contribute to the blood lymphocytopenia observed after intensive and downhill treadmill running in humans.

The lymphocytopenia that occurs during the recovery stage of exercise may be a result of apoptosis through an increased expression of CD95, a loss of the complement regulatory proteins CD55 and CD59, or both. Trained subjects completed intensive, moderate, and downhill treadmill-running protocols. Blood lymphocytes isolated before, immediately after, 1h after, and 24h after each exercise test were assessed for markers of apoptosis (Annexin-V(+), HSP60(+)), and CD55, CD59, and CD95 expression by flow cytometry. Lymphocytopenia occurred 1h after intensive and downhill running exercise, but no changes in the percentage of Annexin-V + or HSP60 + lymphocytes were found. Numbers of CD95(+), CD55(dim), and CD59(dim) lymphocytes increased immediately after intensive and downhill exercise, which were attributed to the selective mobilization and subsequent efflux of CD8(+) and CD56(+) lymphocyte subsets. No differences were found between the intensive and downhill protocols. In conclusion, apoptosis of circulating lymphocytes does not appear to contribute to exercise-induced lymphocytopenia.