Naive and memory T cell subsets are differentially mobilized during physical stress

This study examined the naive and memory phenotypic profiles of CD4+ and CD8(hi) T cells that were mobilized to the peripheral circulation during a combination of aerobic exercise and heat stress, determining expression of the adhesion molecules CD62L and CD11a on the recruited cells. Twelve recreationally active males (age 27.1 +/- 5.3 yr, height 1.77 +/- 0.08 m, mass 76.9 +/- 12.0 kg, VO(2)peal(43.9 +/- 6.7 mL x kg(-1) x min(-1)) completed a 40 min bout of cycle ergometry at 65 % of VO(2)peak while immersed to mid-chest in a water bath at 39degreesC. Venous blood samples were collected before (T-0), during T-40) and 30 min after (T-70) exposure to combined exercise and heat stress. Specimens were analyzed by three-colour flow cytometry for CD4+ and CD8hi T cell expression of CD45RO, CD11a and CD62L. Some 80% of the CD41 T cells that were mobilized were of the CD45RO memory phenotype, with the numbers of CD11a(lo) and CD62L(+) cells increasing more than those of CD11a(hi) and CD62L(-) cells. For the CD8hi cells, there was a more equal recruitment of CD45RO(-) naive (43%) and CD45RO(+) memory (57%) cells. The majority (84%) of recruited CD8(+) cells were CD11ahi; there was a trend to predominance of CD62L- cells (57 %) for the memory subset, but with almost equal recruitment of CD62L(-/-) for the naive subset. We conclude that the exercise + heat stress induced trend to an increase in CD4+ T cells is linked in some way to memory phenotype; it cannot be explained simply by a high density expression of CD11a and lack of the lymph node homing receptor (CD62L). Furthermore, although mobilization of CD8hi T cells is not linked to memory phenotype, a high density expression of CD11a and a lack of the lymph node homing receptor are important determinants of CD8hi T cell mobilization.