title: Effect of a high and low dose of caffeine on antigen-stimulated activation of human natural killer cells after prolonged cycling.
abstract: This study investigated the effect of a high and low dose of caffeine on antigen-stimulated natural killer (NK) cell (CD3- CD56+) activation after prolonged, strenuous cycling, as assessed by the early-activation molecule CD69. In a randomized crossover design, 12 healthy male endurance-trained cyclists cycled for 90 min at 70% VO2peak 60 min after ingesting either 0 (PLA), 2 (2CAF), or 6 (6CAF) mg/kg body mass of caffeine. Whole blood was stimulated with Pediacel (5 in 1) vaccine. A high dose of caffeine (6CAF) increased the number of CD3-CD56+ cells in the circulation immediately postexercise compared with PLA (p < .05). For both 2CAF and 6CAF, the geometric mean fluorescence intensity (GMFI) of CD69+ expression on unstimulated CD3-CD56+ cells was significantly higher than with PLA (both p < .05). When cells were stimulated with antigen, the GMFI of CD69 expression remained significantly higher with 2CAF than with PLA 1 hr postexercise (p < .05). Although not achieving statistical significance, 6CAF also followed a similar trend when stimulated (p = .09). There were no differences in GMFI of CD69 expression between 2CAF and 6CAF. These results suggest that a high (6 mg/kg) dose of caffeine was associated with the recruitment of NK cells into the circulation and that both a high and low (2 mg/kg) dose of caffeine increased unstimulated and antigen-stimulated NK-cell activation 1 hr after high-intensity exercise. Furthermore, there does not appear to be a dose-dependent effect of caffeine on NK-cell activation 1 hr after prolonged intensive cycling.
authors.affiliation: School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK.
authors.forename: Deborah K
authors.initials: DK
authors.lastname: Fletcher
authors.forename: Nicolette C
authors.initials: NC
authors.lastname: Bishop
mesh_terms: D000284:Administration, Oral; D015703:Antigens, CD / Q000032:analysis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D001642:Bicycling / Q000502:physiology*; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D018592:Cross-Over Studies; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology* / Q000502:physiology; D037181:Lectins, C-Type / Q000032:analysis; D008213:Lymphocyte Activation; D008297:Male; D010101:Oxygen Consumption; D055815:Young Adult; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D002110:Caffeine; D000697:Central Nervous System Stimulants; D037181:Lectins, C-Type; D000099192:CD69 Antigens