Patterns of
fibrin deposition were investigated by immunofluorescence microscopy in livers of thymus intact (TI) and athymic (AT) mice infected with Schistosoma mansoni.
Thrombin and fibrinolysis inhibitor activity in
tissue extracts also were measured. In TI mice
fibrin was detected perivascularly by 6 weeks after
infection and at 8 weeks it was found over the
granulomas as they developed.
Fibrin was cleared from the center of
granulomas by 10 weeks.
Thrombin inhibitor activity increased at 4 to 6 weeks but declined below control levels later as
granulomas formed. Fibronolysis inhibitor activity, on the other hand, peaked at 9 to 12 weeks after
infection. In AT mice extensive
fibrin deposition was detected in the liver throughout the period when smaller and incomplete
granulomas developed. Central clearing did not occur.
Thrombin inhibitor activity greatly increased by 8 weeks after
infection but fibrinolysis inhibitor activity remained unchanged. These findings suggest that
fibrin deposition and firbinolysis are orderly events regulated in the lesions by
proteinases and their inhibitors and this seems to be a general tissue reaction in the early stage of chronic
granuloma formation. Since local clearance of
fibrin in vivo and fibrinolysis inhibitor activity from
tissue extracts studied in vitro are more evident in TI mice than in AT mice, it appears that T cell fu;ction is important in modulating the tissue response during granulomatous
inflammation.