The effects of marathon running on expression of the complement regulatory proteins CD55 (DAF) and CD59 (MACIF) on red blood cells.

Exercise is known to result in the haemolysis of red blood cells (RBCs). Although mechanical stressors such as footstrike and an increased velocity of blood flow may be involved, the biological mechanisms that underpin RBC haemolysis remain elusive. RBCs are potentially susceptible to lysis by autologous complement activation. RBCs are protected from the lytic effects of complement by regulatory proteins (CRPs) bound to the cell membrane via glycosylphosphatidylinositol (GPI) anchors. This study aimed to determine if marathon running would result in RBC haemolysis through a loss of membrane expression of the CRPs CD55 (decay accelerating factor) and CD59 (membrane attack complex inhibitory factor). Blood samples were obtained from 14 male runners before, within 30 min after, and 24 h after completion of the 2004 London Marathon. RBCs were assessed for cell surface CD55 and CD59 expression using indirect immunofluorescence assays and flow cytometry. No significant changes in the total RBC count, haematocrit or haemoglobin concentrations were found in response to running the marathon (P > 0.05). Blood bilirubin concentrations after the marathon were significantly greater than the pre-race values (P < 0.01). The relative fluorescent intensity (arbitrary units) of CD55 and CD59 expression on RBC membranes did not change in response to the marathon race (P > 0.05). In conclusion, marathon running did not alter the expression of CD55 or CD59 on RBCs, despite concomitant elevations in blood bilirubin concentrations. Consequently, any haemolysis of RBCs that occurred in response to the marathon was not likely due to a loss of membrane bound CRPs and subsequent cell lysis by autologous complement.