Granulocyte and monocyte CD11b expression during plasma separation is dependent on complement factor 5 (C5) – an ex vivo study with blood from a C5-deficient individual

Abstract

The aim of the study was to investigate the role of complement factor 5 (C5) in reactions elicited by plasma separation using blood from a C5‐deficient (C5D) individual, comparing it to C5‐deficient blood reconstituted with C5 (C5DR) and blood from healthy donors. Blood was circulated through an <i>ex vivo</i> plasma separation model. Leukocyte CD11b expression and leukocyte–platelet conjugates were measured by flow cytometry during a 30‐min period. Other markers were assessed during a 240‐min period. Granulocyte and monocyte CD11b expression did not increase in C5D blood during plasma separation. In C5DR samples granulocytes CD11b expression, measured by mean fluorescence intensity (MFI), increased from 10481 ± 6022 (SD) to 62703 ± 4936, and monocytes CD11b expression changed from 13837 ± 7047 to 40063 ± 713. Granulocyte–platelet conjugates showed a 2.5‐fold increase in the C5DR sample compared to the C5D sample. Monocyte–platelet conjugates increased independently of C5. In the C5D samples, platelet count decreased from 210 × 10⁹/L (201–219) (median and range) to 51 × 10⁹/L (50–51), and C3bc increased from 14 CAU/mL (21–7) to 198 CAU/mL (127–269), whereas TCC formation was blocked during plasma separation. In conclusion, up‐regulation of granulocyte and monocyte CD11b during plasma separation was C5‐dependent. The results also indicate C5 dependency in granulocyte–platelet conjugates formation.