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Infection and Immunity, February 2006, p. 1181-1188, Vol. 74, No. 2
0019-9567/06/$08.00+0 doi:10.1128/IAI.74.2.1181-1188.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Trudeau Institute, Saranac Lake, New York
Received 23 August 2005/ Returned for modification 10 October 2005/ Accepted 29 November 2005
While coagulation often causes pathology during infectious disease, we recently demonstrated that fibrin, a product of the coagulation pathway, performs a critical protective function during acute toxoplasmosis (L. L. Johnson, K. N. Berggren, F. M. Szaba, W. Chen, and S. T. Smiley, J. Exp. Med. 197:801-806, 2003). Here, we investigate the mechanisms regulating the formation of this protective fibrin. Through comparisons of Toxoplasma-infected wild-type and cytokine-deficient mice we dissociate, for the first time, the relative fibrin-regulating capacities of pathogen products, host cytokines, and infection-stimulated hemorrhage. Remarkably, neither the pathogen burden nor hemorrhage is a primary regulator of fibrin levels. Rather, two type 1 cytokines exert dominant and counterregulatory roles: tumor necrosis factor alpha (TNF-
), acting via the type 1 TNF-
receptor, promotes fibrin deposition, while gamma interferon (IFN-
), acting via STAT1 and IFN-
receptors expressed on radioresistant cells, suppresses fibrin deposition. These findings have important clinical implications, as they establish that cytokines known to regulate pathological coagulation also dictate levels of protective fibrin deposition. We present a novel model depicting mechanisms by which the immune system can destroy infected tissue while independently restraining hemorrhage and promoting tissue repair through the deliberate deposition of protective fibrin.
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