A novel conditional platelet depletion mouse model reveals the importance of platelets in protection against Staphylococcus aureus bacteremia

Abstract

Background Platelets are critical cells for maintaining vascular hemostasis but their activities in other processes are becoming apparent. Specifically, the ability of platelets to recognize and respond to infectious agents is an important area of investigation. To understand the physiological roles of platelets in vivo, most researchers have used antibody-mediated platelet depletion, which has certain limitations. Objective To develop an optimal system to study the contribution of platelets to protection from S. aureus blood infection. Methods Here we describe a novel experimental model of conditional platelet depletion based on the Cre-recombinase cell ablation system. Using this technology, the simian diphtheria toxin receptor was expressed in platelet factor 4 (PF4) positive cells (megakaryocytes and platelets). Results Systemic administration of diphtheria toxin (DT) every 48 hours results in reduced platelet numbers that become undetectable after six days. While platelets are depleted, no other blood cells are affected. Using this newly-developed model, the functional contributions of platelets in protection against Staphylococcus aureus (S. aureus) bacteremia was examined. Platelet-depleted mice succumbed to infection more rapidly than wild-type (WT) mice and contained significantly higher bacterial burden in kidneys, increased serum markers of kidney damage and elevated levels of cytokines indicative of septic shock. Conclusions Here we illustrate a new mouse model for conditional platelet depletion and implicate platelets as important participants of the immune response to bacterial blood infections.

Platelets Mediate Host Defense against Staphylococcus aureus through Direct Bactericidal Activity and by Enhancing Macrophage Activities

“…Platelets engage the immune system by interacting with various immune cells (34, 35), and participate in both innate and adaptive immune responses. Our recent publication indicate that platelets provide protection to S. aureus infection (19). Based on this observation, the goal of the present study was to further elucidate the mechanistic details of how platelets promote protection against S. aureus infection and whether this occurs directly and/or through the potentiation of leukocytes antimicrobial functions.…”

“…Recent reports by us and others showed that platelets functionally contribute to protection against S. aureus infection (19–23). Using our novel inducible platelet-depleted mouse model, we demonstrated that platelet-depleted mice have high bacterial burden in kidneys, a more severe cytokine storm, and decreased survival compared to WT counterparts (19).…”

“…Using our novel inducible platelet-depleted mouse model, we demonstrated that platelet-depleted mice have high bacterial burden in kidneys, a more severe cytokine storm, and decreased survival compared to WT counterparts (19). However, the mechanistic detail of how platelets participate in host defense against S. aureus infection is not clearly understood.…”

The phospholipase D superfamily as therapeutic targets

“…A therapeutic lacking hemorrhage risks would provide an important potential advance for the field. However, this is a parameter that would need to be assessed clinically, since mice are less dependent on platelet activation for hemostasis than humans [41]. …”

Identification of a murine CD45−F4/80lo HSC-derived marrow endosteal cell associated with donor stem cell engraftment

“…Mice received 100 ng of diphtheria toxin (DT) intraperitoneally 24 hours before TBI (1000 cGy) and were analyzed 48 hours after irradiation. Monocytes, macrophages, or megakaryocytes were depleted in transgenic mice expressing iDTR on lysozyme2-expressing (LYZ-Cre) 24 or PF4-expressing cells, 25,26 respectively. Mice received daily intraperitoneal injections of DT (100 ng) for 6 days, received TBI on day 4 (1000 cGy), and were analyzed 48 hours after irradiation.…”