Immobilized IgG and fibrinogen differentially affect the cytoskeletal organization and bactericidal function of...

The infection of a vascular prosthesis is a dreaded clinical outcome. Since fibrinogen (FBGN) and immunoglobulin (IgG) coat the implanted biomaterial surface, it is with these immobilized proteins that the neutrophil (PMN) interacts. This study tests the hypothesis that PMN are impaired in their ability to kill bacteria when bound to immobilized IgG or FBGN. Isolated human PMN were bound to FBGN or IgG and then left untreated or exposed to phorbol myristate acetate (PMA; 10(-7) M). PMN adhered loosely, but did not spread, onto FBGN. In contrast, PMN spread fully onto IgG, exhibiting polarized pseudopodia. PMA treatment induced spreading of the FBGN bound cells. Suspended and adherent PMN were incubated 1 h with 14C-labeled Staphylococcus aureus; then, phagocytosis was assessed by radioactive uptake or bacterial kill was determined by plating recovered bacteria and colony counting. Data were analyzed by unpaired t test. We observed that both the phagocytic and the killing ability of FBGN-bound PMN were similar to that of suspended PMN. Conversely, IgG-bound PMN displayed a 62 +/- 6% (P < 0.01) decrease in phagocytosis and 33 +/- 7% (P < 0.05) reduction in kill vs suspended cells. PMA induced a 74 +/- 6% (P < 0.01) reduction in phagocytosis and 68 +/- 5% (P < 0.01) reduction in kill of bacteria for PMN bound to FBGN with no further effect on IgG-bound PMN. Using fluorescent vital dyes and confocal microscopy we determined that 33% fewer PMN were engaged in phagocytosis when bound to IgG vs FBGN. We conclude that Fc receptor ligation by immobilized IgG or PMA treatment of the FBGN-adherent PMN triggers cell spreading and reduced bactericidal activity. These results indicate that excessive cytoskeletal organization may impair the ability of PMN to kill bacteria and result in vascular graft infections.