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Cryptococcus neoformans is resistant to surfactant protein A mediated host defense mechanisms.

Giles SS, Zaas AK, Reidy MF, Perfect JR, Wright JR - PLoS ONE (2007)

Bottom Line: Using in vitro binding assays we confirmed that SP-A does not directly bind to a fully encapsulated strain of C. neoformans (H99).We found that the immune response assessed by cellular counts, TNFalpha cytokine production, and fungal burden in lungs and bronchoalveolar lavage fluids during early stages of infection were equivalent.Our results suggest that unlike a variety of bacteria, viruses, and other fungi, progression of disease with an inhalational challenge of C. neoformans does not appear to be negatively or positively affected by SP-A mediated mechanisms of pulmonary host defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America.

ABSTRACT
Initiation of a protective immune response to infection by the pathogenic fungus Cryptococcus neoformans is mediated in part by host factors that promote interactions between immune cells and C. neoformans yeast. Surfactant protein A (SP-A) contributes positively to pulmonary host defenses against a variety of bacteria, viruses, and fungi in part by promoting the recognition and phagocytosis of these pathogens by alveolar macrophages. In the present study we investigated the role of SP-A as a mediator of host defense against the pulmonary pathogen, C. neoformans. Previous studies have shown that SP-A binds to acapsular and minimally encapsulated strains of C. neoformans. Using in vitro binding assays we confirmed that SP-A does not directly bind to a fully encapsulated strain of C. neoformans (H99). However, we observed that when C. neoformans was incubated in bronchoalveolar fluid, SP-A binding was detected, suggesting that another alveolar host factor may enable SP-A binding. Indeed, we discovered that SP-A binds encapsulated C. neoformans via a previously unknown IgG dependent mechanism. The consequence of this interaction was the inhibition of IgG-mediated phagocytosis of C. neoformans by alveolar macrophages. Therefore, to assess the contribution of SP-A to the pulmonary host defenses we compared in vivo infections using SP-A mice (SP-A-/-) and wild-type mice in an intranasal infection model. We found that the immune response assessed by cellular counts, TNFalpha cytokine production, and fungal burden in lungs and bronchoalveolar lavage fluids during early stages of infection were equivalent. Furthermore, the survival outcome of C. neoformans infection was equivalent in SP-A-/- and wild-type mice. Our results suggest that unlike a variety of bacteria, viruses, and other fungi, progression of disease with an inhalational challenge of C. neoformans does not appear to be negatively or positively affected by SP-A mediated mechanisms of pulmonary host defense.

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SP-A inhibits the uptake of IgG opsonized C. neoformans by alveolar macrophages.Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100%. SP-A (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of IgG opsonized C. neoformans (1×105) by alveolar macrophages (1×105) in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively). Results represent the mean plus or minus the standard error of the mean of three experiments.
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pone-0001370-g003: SP-A inhibits the uptake of IgG opsonized C. neoformans by alveolar macrophages.Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100%. SP-A (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of IgG opsonized C. neoformans (1×105) by alveolar macrophages (1×105) in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively). Results represent the mean plus or minus the standard error of the mean of three experiments.

Mentions: We next investigated whether SP-A binding could functionally affect IgG-mediated phagocytosis of C. neoformans by alveolar macrophages in vitro. For these experiments C. neoformans cells were fluorescently labeled with AF-647, which had no affect on C. neoformans uptake by alveolar macrophages in preliminary experiments (results not shown). Attachment/phagocytosis was quantified by flow cytometry. Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100% (Figure 3). We observed that all the SP-A concentrations tested (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of anti-GXM IgG opsonized C. neoformans yeast by alveolar macrophages and that this inhibition occurred in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively) (Figure 3). These results demonstrate a unique mechanism by which SP-A inhibits, rather than enhances, the phagocytosis of an antibody opsonized microorganism by alveolar macrophages.


Cryptococcus neoformans is resistant to surfactant protein A mediated host defense mechanisms.

Giles SS, Zaas AK, Reidy MF, Perfect JR, Wright JR - PLoS ONE (2007)

SP-A inhibits the uptake of IgG opsonized C. neoformans by alveolar macrophages.Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100%. SP-A (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of IgG opsonized C. neoformans (1×105) by alveolar macrophages (1×105) in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively). Results represent the mean plus or minus the standard error of the mean of three experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2147053&req=5

pone-0001370-g003: SP-A inhibits the uptake of IgG opsonized C. neoformans by alveolar macrophages.Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100%. SP-A (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of IgG opsonized C. neoformans (1×105) by alveolar macrophages (1×105) in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively). Results represent the mean plus or minus the standard error of the mean of three experiments.
Mentions: We next investigated whether SP-A binding could functionally affect IgG-mediated phagocytosis of C. neoformans by alveolar macrophages in vitro. For these experiments C. neoformans cells were fluorescently labeled with AF-647, which had no affect on C. neoformans uptake by alveolar macrophages in preliminary experiments (results not shown). Attachment/phagocytosis was quantified by flow cytometry. Non-IgG opsonized C. neoformans were attached/phagocytosed by less than 1% of the alveolar macrophage population in the presence or absence of SP-A, thus percent inhibition of uptake for these conditions is presented as ∼100% (Figure 3). We observed that all the SP-A concentrations tested (20, 40 and 80 µg/ml) significantly (P<0.001) inhibited the uptake of anti-GXM IgG opsonized C. neoformans yeast by alveolar macrophages and that this inhibition occurred in a dose dependent manner (16±3.1%, 34±2.7% and 46±3.0%, respectively) (Figure 3). These results demonstrate a unique mechanism by which SP-A inhibits, rather than enhances, the phagocytosis of an antibody opsonized microorganism by alveolar macrophages.

Bottom Line: Using in vitro binding assays we confirmed that SP-A does not directly bind to a fully encapsulated strain of C. neoformans (H99).We found that the immune response assessed by cellular counts, TNFalpha cytokine production, and fungal burden in lungs and bronchoalveolar lavage fluids during early stages of infection were equivalent.Our results suggest that unlike a variety of bacteria, viruses, and other fungi, progression of disease with an inhalational challenge of C. neoformans does not appear to be negatively or positively affected by SP-A mediated mechanisms of pulmonary host defense.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America.

ABSTRACT
Initiation of a protective immune response to infection by the pathogenic fungus Cryptococcus neoformans is mediated in part by host factors that promote interactions between immune cells and C. neoformans yeast. Surfactant protein A (SP-A) contributes positively to pulmonary host defenses against a variety of bacteria, viruses, and fungi in part by promoting the recognition and phagocytosis of these pathogens by alveolar macrophages. In the present study we investigated the role of SP-A as a mediator of host defense against the pulmonary pathogen, C. neoformans. Previous studies have shown that SP-A binds to acapsular and minimally encapsulated strains of C. neoformans. Using in vitro binding assays we confirmed that SP-A does not directly bind to a fully encapsulated strain of C. neoformans (H99). However, we observed that when C. neoformans was incubated in bronchoalveolar fluid, SP-A binding was detected, suggesting that another alveolar host factor may enable SP-A binding. Indeed, we discovered that SP-A binds encapsulated C. neoformans via a previously unknown IgG dependent mechanism. The consequence of this interaction was the inhibition of IgG-mediated phagocytosis of C. neoformans by alveolar macrophages. Therefore, to assess the contribution of SP-A to the pulmonary host defenses we compared in vivo infections using SP-A mice (SP-A-/-) and wild-type mice in an intranasal infection model. We found that the immune response assessed by cellular counts, TNFalpha cytokine production, and fungal burden in lungs and bronchoalveolar lavage fluids during early stages of infection were equivalent. Furthermore, the survival outcome of C. neoformans infection was equivalent in SP-A-/- and wild-type mice. Our results suggest that unlike a variety of bacteria, viruses, and other fungi, progression of disease with an inhalational challenge of C. neoformans does not appear to be negatively or positively affected by SP-A mediated mechanisms of pulmonary host defense.

Show MeSH
Related in: MedlinePlus