Summary
Plasminogen knock-out (PG−/−) mice provide an unique opportunity for the study of alternative mediators of
fibrinolysis. Polymorphonuclear leucocytes (PMNs) contain non-plasmin fibrinolytic
proteases, however the degree to which these cells contribute to fibrin(ogen) degradation
in these animals is not known. Thrombi were generated in carotid arteries and jugular
veins of PG−/− and wild type (PG+/+) mice following adventitial application of a 20% ferric chloride solution. PMNs,
identified histologically on H&E staining and by immunohistochemistry using anti-mouse
PMN RB6-8C5 antibody, accumulated within the thrombus by 6 h after the injury and
peaked at 24 h. There was significantly greater retention of PMNs within the thrombi
of PG−/− mice from 48 to 72 h than in the PG+/+ controls (at 72 h: PG−/− 255 ± 41 cell/mm2 (n = 5), PG+/+ 61 ± 10 cell/mm2 (n = 5), p <0.01 in the arterial thrombi; PG−/− 252 ± 50 cell/mm2 (n = 5), PG+/+ 100 ± 36 cell/mm2 (n = 5), p <0.05 in the venous thrombi), providing potential for more PMN derived
fibrinolytic enzymes to be present at late times after a thrombotic challenge in PG−/− mice relative to the PG+/+ controls.
Intact PMNs were elicited from the peritoneal cavities of PG−/− and PG+/+ mice following 4% thioglycolate stimulation. In vitro studies showed PMNs from PG−/− mice to release greater quantities of 10% trichloroacetic acid (TCA)-soluble fibrinopeptides
from I125-labeled fibrinogen, than cells from PG+/+ controls although these differences did not become apparent until after 24 h of incubation
(at 72 h incubation: PG−/− 918 n /10 X 106 cells/0.5 ml, PG+/+ 589 ng/10 X 106 cells/ ml p = 0.005). Furthermore, autoradiographic analysis of the I125labeled fibrinogen degradation products showed the cleavage pattern by PG−/− PMNs to be distinct from that produced by PG+/+ PMNs.
These data suggest that a relatively greater role for PMNs-initiated fibrinolysis
exists in the setting of plasminogen deficiency, although this prominence only becomes
evident more than 24 h after the thrombotic insult. In addition, mechanisms responsible
for the process in PG−/− mice may be distinct from those primarily responsible for the process in PMNs
from PG+/+ mice.
Keywords
Fibrinolysis - plasminogen deficiency - polymorphonuclear leucocytes