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Infection and Immunity, January 2002, p. 350-359, Vol. 70, No. 1
0019-9567/01/$04.00+0     DOI: 10.1128/IAI.70.1.350-359.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

M⁺ Group A Streptococci Are Phagocytized and Killed in Whole Blood by C5a-Activated Polymorphonuclear Leukocytes

Eric DeMaster,¹ Norbert Schnitzler,² Qi Cheng,¹ and Patrick Cleary^1*

Department of Microbiology, University of Minnesota, Minneapolis, Minnesota,¹ Institute of Medical Microbiology and National Reference Laboratory for Streptococci, University Hospital, Aachen, Germany²

Received 6 August 2001/ Returned for modification 26 September 2001/ Accepted 10 October 2001

Historically, resistance to phagocytosis has been determined by incubating group A streptococci in human blood and comparing the numbers of CFU before and after incubation. Utilizing a flow cytometry-based technique, we have investigated the phagocytosis of M⁺ group A streptococci by polymorphonuclear leukocytes (PMNs) in heparinized human peripheral whole blood. Intracellular labeling of streptococci with a nontoxic fluorescent dye allowed us to quantify the association and phagocytosis of M⁺ streptococci by PMNs in whole blood in the presence or absence of C5a, a physiologically important chemotactic activator of PMNs. We found that wild-type strains of group A streptococci that are resistant to phagocytosis (determined by the classical Lancefield method) readily associate with C5a-activated whole-blood PMNs. In the absence of opsonizing M-type-specific antibodies, the M⁺ streptococci associated with PMNs are phagocytized and killed. In addition, blockade of the ß₂ integrin, CD11b/CD18, with anti-human CD11b monoclonal antibody inhibited association between M⁺ streptococci and C5a-activated PMNs. These findings establish a new relationship between M⁺ streptococci and PMNs, in which C5a-activated PMNs have the capacity to kill M⁺ streptococci in whole blood through a receptor-mediated phagocytic mechanism.

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* Corresponding author. Mailing address: Department of Microbiology, University of Minnesota, Minneapolis, MN 55455. Phone: (612) 624-6190. Fax: (612) 626-0623. E-mail: cleary{at}lenti.med.umn.edu.

Editor: T. R. Kozel

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Infection and Immunity, January 2002, p. 350-359, Vol. 70, No. 1
0019-9567/01/$04.00+0     DOI: 10.1128/IAI.70.1.350-359.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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