Parabolic flight primes cytotoxic capabilities of polymorphonuclear leucocytes in humans

Background Previously performed in vitro studies suggested that gravitational stress may alter functions of immune cells. This study investigated the in vivo effects of parabolic flight manoeuvres as a short‐term model of micro‐ and hypergravity on the cytotoxic and microbicidal polymorphonuclear leucocyte (PMN) functions as the key element of innate immunity. Material and methods Twenty‐one healthy male volunteers underwent 30 subsequent parabolic flight manoeuvres. Each manoeuvre produced 22‐s periods of nearly weightlessness close to «0g», with each parabola starting with a pull‐up and ending with a pull‐out (hypergravity) at 1·8 g for about 20 s each. Blood samples were drawn 24 h prior to take off (T0), after 25–30 parabolas (T1), and 24 h (T2) and 48 h (T3) after flight for determination of (i) leucocyte number and subpopulations, (ii) PMNs’ capabilities to produce hydrogen peroxide (H₂O₂) and to adhere and phagocytose particles and (iii) plasma cytokines known to prime PMN functions interleukin‐8 (IL‐8), tumour necrosis factor‐α (TNF‐α), granulocyte‐colony stimulating factor (G‐CSF) and granulocyte‐macrophage colony stimulating factor (GM‐CSF)]. Results Parabolic flight induced an increase in leucocyte number with a significant elevation of the PMN fraction. The spontaneous H₂O₂ production by PMNs did not change; however, the capability of PMNs to produce H₂O₂ in response to soluble stimuli N‐formyl‐methionyl‐leucyl‐phenylalanine (fMLP), fMLP and TNF‐α, calcium ionophore (A23187), phorbol myristate acetate (PMA)] was increased. Adhesive and phagocytic properties of PMNs were not altered. Regarding priming cytokines, IL‐8 and G‐CSF were significantly elevated. Conclusions Our data indicate that parabolic flight induces priming of the cytotoxic capabilities of PMNs without affecting microbicidal functions.