title: M(+) group a streptococci are phagocytized and killed in whole blood by C5a-activated polymorphonuclear leukocytes.
abstract: 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 beta(2) 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.
authors.affiliation: Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: DeMaster
authors.forename: Norbert
authors.initials: N
authors.lastname: Schnitzler
authors.forename: Qi
authors.initials: Q
authors.lastname: Cheng
authors.forename: Patrick
authors.initials: P
authors.lastname: Cleary
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D018821:CD18 Antigens / Q000276:immunology; D015936:Complement C5a / Q000276:immunology*; D017242:Complement Factor H / Q000276:immunology; D006801:Humans; D016177:Macrophage-1 Antigen / Q000276:immunology; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D013297:Streptococcus pyogenes / Q000254:growth & development / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D018821:CD18 Antigens; C493495:CFH protein, human; D016177:Macrophage-1 Antigen; D015936:Complement C5a; D017242:Complement Factor H