title: Alveolar macrophage-mediated killing of Pneumocystis carinii f. sp. muris involves molecular recognition by the Dectin-1 beta-glucan receptor.
abstract: Innate immune mechanisms against Pneumocystis carinii, a frequent cause of pneumonia in immunocompromised individuals, are not well understood. Using both real time polymerase chain reaction as a measure of organism viability and fluorescent deconvolution microscopy, we show that nonopsonic phagocytosis of P. carinii by alveolar macrophages is mediated by the Dectin-1 beta-glucan receptor and that the subsequent generation of hydrogen peroxide is involved in alveolar macrophage-mediated killing of P. carinii. The macrophage Dectin-1 beta-glucan receptor colocalized with the P. carinii cyst wall. However, blockage of Dectin-1 with high concentrations of anti-Dectin-1 antibody inhibited binding and concomitant killing of P. carinii by alveolar macrophages. Furthermore, RAW 264.7 macrophages overexpressing Dectin-1 bound P. carinii at a higher level than control RAW cells. In the presence of Dectin-1 blockage, killing of opsonized P. carinii could be restored through FcgammaRII/III receptors. Opsonized P. carinii could also be efficiently killed in the presence of FcgammaRII/III receptor blockage through Dectin-1-mediated phagocytosis. We further show that Dectin-1 is required for P. carinii-induced macrophage inflammatory protein 2 production by alveolar macrophages. Taken together, these results show that nonopsonic phagocytosis and subsequent killing of P. carinii by alveolar macrophages is dependent upon recognition by the Dectin-1 beta-glucan receptor.
authors.affiliation: Department of Pediatrics, Division of Pulmonology, Children's Hospital of Pittsburgh, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Chad
authors.initials: C
authors.lastname: Steele
authors.forename: Luis
authors.initials: L
authors.lastname: Marrero
authors.forename: Steve
authors.initials: S
authors.lastname: Swain
authors.forename: Allen G
authors.initials: AG
authors.lastname: Harmsen
authors.forename: Mingquan
authors.initials: M
authors.lastname: Zheng
authors.forename: Gordon D
authors.initials: GD
authors.lastname: Brown
authors.forename: Siamon
authors.initials: S
authors.lastname: Gordon
authors.forename: Judd E
authors.initials: JE
authors.lastname: Shellito
authors.forename: Jay K
authors.initials: JK
authors.lastname: Kolls
mesh_terms: D000818:Animals; D002460:Cell Line; D054426:Chemokine CXCL2; D037181:Lectins, C-Type; D016676:Macrophages, Alveolar / Q000276:immunology*; D008297:Male; D008565:Membrane Proteins / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D015846:Monokines / Q000096:biosynthesis; D009419:Nerve Tissue Proteins / Q000276:immunology*; D010587:Phagocytosis; D045363:Pneumocystis carinii / Q000276:immunology*; D017382:Reactive Oxygen Species; D011971:Receptors, Immunologic / Q000276:immunology*; D000099181:Dectin-1
chemical_list: D054426:Chemokine CXCL2; D037181:Lectins, C-Type; D008565:Membrane Proteins; D015846:Monokines; D009419:Nerve Tissue Proteins; D017382:Reactive Oxygen Species; D011971:Receptors, Immunologic; D000099181:Dectin-1; C045268:beta-glucan receptor