Recruited macrophages control dissemination of group A Streptococcus from infected soft tissues.
Group A Streptococcus (GAS) causes diverse infections in humans, ranging from mild to life-threatening invasive diseases, such as necrotizing fasciitis (NF), a rapidly progressing deep tissue infection. Despite prompt treatments, NF remains a significant cause of morbidity and mortality, even in previously healthy individuals. The early recruitment of leukocytes is crucial to the outcome of NF; however, although the role of polymorphonuclear neutrophils (PMNs) in host defense against NF is well established, the role of recruited macrophages remains poorly defined. Using a cutaneous murine model mimicking human NF, we found that mice deficient in TNF-α were highly susceptible to s.c. infections with GAS, and a paucity of macrophages, but not PMNs, was demonstrated. To test whether the effects of TNF-α on the outcome of infection are mediated by macrophages/monocytes, we systemically depleted C57BL/6 mice of monocytes by pharmacological and genetic approaches. Systemic monocyte depletion substantially increased bacterial dissemination from soft tissues without affecting the number of recruited PMNs or altering the bacterial loads in soft tissues. Enhanced GAS dissemination could be reverted by either i.v. injection of monocytes or s.c. administration of peritoneal macrophages. These experiments demonstrated that recruited macrophages play a key role in defense against the extracellular pathogen GAS by limiting its spread from soft tissues.
Department of Microbiology and Molecular Genetics, Faculty of Medicine, The Institute for Medical Research - Israel-Canada, The Hebrew University, Jerusalem 91120, Israel.
Inbal
I
Mishalian
Merav
M
Ordan
Amnon
A
Peled
Alexander
A
Maly
Miriam B
MB
Eichenbaum
Miriam
M
Ravins
Tegest
T
Aychek
Steffen
S
Jung
Emanuel
E
Hanski
D000818:Animals; D002469:Cell Separation; D016207:Cytokines / Q000096:biosynthesis; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D019115:Fasciitis, Necrotizing / Q000276:immunology*; D005434:Flow Cytometry; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D013290:Streptococcal Infections / Q000276:immunology*; D013297:Streptococcus pyogenes / Q000276:immunology
D016207:Cytokines