Surfactant protein D increases phagocytosis of hypocapsular Cryptococcus neoformans by murine macrophages and enhances fungal survival.
Cryptococcus neoformans is a facultative intracellular opportunistic pathogen and the leading cause of fungal meningitis in humans. In the absence of a protective cellular immune response, the inhalation of C. neoformans cells or spores results in pulmonary infection. C. neoformans cells produce a polysaccharide capsule composed predominantly of glucuronoxylomannan, which constitutes approximately 90% of the capsular material. In the lungs, surfactant protein A (SP-A) and SP-D contribute to immune defense by facilitating the aggregation, uptake, and killing of many microorganisms by phagocytic cells. We hypothesized that SP-D plays a role in C. neoformans pathogenesis by binding to and enhancing the phagocytosis of the yeast. Here, the abilities of SP-D to bind to and facilitate the phagocytosis and survival of the wild-type encapsulated strain H99 and the cap59Delta mutant hypocapsular strain are assessed. SP-D binding to cap59Delta mutant cells was approximately sixfold greater than binding to wild-type cells. SP-D enhanced the phagocytosis of cap59Delta cells by approximately fourfold in vitro. To investigate SP-D binding in vivo, SP-D(-/-) mice were intranasally inoculated with Alexa Fluor 488-labeled cap59Delta or H99 cells. By confocal microscopy, a greater number of phagocytosed C. neoformans cells in wild-type mice than in SP-D(-/-) mice was observed, consistent with in vitro data. Interestingly, SP-D protected C. neoformans cells against macrophage-mediated defense mechanisms in vitro, as demonstrated by an analysis of fungal viability using a CFU assay. These findings provide evidence that C. neoformans subverts host defense mechanisms involving surfactant, establishing a novel virulence paradigm that may be targeted for therapy.
Geunes-Boyer
Scarlett
S
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Oliver
Timothy N
TN
Janbon
Guilhem
G
Lodge
Jennifer K
JK
Heitman
Joseph
J
Perfect
John R
JR
Wright
Jo Rae
JR
D000818:Animals; D002460:Cell Line; D015169:Colony Count, Microbial; D003455:Cryptococcus neoformans / Q000276:immunology*; D008264:Macrophages / Q000382:microbiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050296:Microbial Viability; D010587:Phagocytosis; D011485:Protein Binding; D037663:Pulmonary Surfactant-Associated Protein D / Q000172:deficiency / Q000276:immunology* / Q000378:metabolism
D037663:Pulmonary Surfactant-Associated Protein D