Increased concentration of the complement split product C5a in acute pyelonephritis during pregnancy

Objective. Pregnant women with acute pyelonephritis develop acute respiratory distress syndrome (ARDS) more frequently than non-pregnant women. The reasons for this remain unknown. The complement system is a complex set of self-assembling proteins that have been implicated in the pathophysiology of ARDS and sepsis. The purpose of this study was to determine if activation of the complement system occurs in pregnant women with acute pyelonephritis. Methods. A cross-sectional study was conducted to determine the plasma concentrations of C3a, C4a and C5a (i.e., complement split products) in pregnant patients with acute pyelonephritis (n = 38) and normal pregnant women (n = 38). The complement split products C3a, C4a and C5a were measured using ELISA. Data were analyzed using non-parametric statistics. Results. 1) The median plasma concentration of C5a in pregnant patients with acute pyelonephritis was significantly higher than that in normal pregnant women (p < 0.001); 2) there was no statistical difference in the median plasma concentration of C3a and C4a between the two groups (p > 0.05); and 3) concentrations of C3a, C4a and C5a were not different among patients with acute pyelonephritis with and without bacteremia. Conclusions. 1) Pyelonephritis in pregnant women is associated with an increased plasma concentration of C5a, but not C3a and C4a; and 2) an excess of C5a can predispose pregnant women to develop ARDS and multi-organ failure in pyelonephritis. This finding may have clinical implications since blocking C5a improves ARDS in experimental sepsis.