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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 does not directly bind to encapsulated C. neoformans yeast.(A.) C. neoformans (1×105) were treated with Alexa Flour 488 labeled SP-A (20 µg/ml) for 60 minutes at 37°C. Surfactant protein binding was quantified by flow cytometric analysis. SP-A binding was not detected. (B.) In contrast, C. neoformans (1×105) treated with undiluted BAL exhibited a small amount of SP-A binding. Results are one representative experiment of at least three (A.) or two (B.) experiments performed.
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pone-0001370-g001: SP-A does not directly bind to encapsulated C. neoformans yeast.(A.) C. neoformans (1×105) were treated with Alexa Flour 488 labeled SP-A (20 µg/ml) for 60 minutes at 37°C. Surfactant protein binding was quantified by flow cytometric analysis. SP-A binding was not detected. (B.) In contrast, C. neoformans (1×105) treated with undiluted BAL exhibited a small amount of SP-A binding. Results are one representative experiment of at least three (A.) or two (B.) experiments performed.

Mentions: Previous studies by Walenkamp et al. and Schelenz et al. showed that in vitro, SP-A binding is restricted to acapsular and minimally encapsulated strains of C. neoformans [10], [11]. To confirm these results, we performed flow cytometry to quantify AF488 labeled SP-A binding to encapsulated C. neoformans yeast (1×105). SP-A binding assays using Escherichia coli HB101 were performed to confirm the binding activity of all SP-A preparations (results not shown). Our results were consistent with those of previous studies; we did not observe SP-A binding to encapsulated H99 C. neoformans yeasts (Figure 1A). To extend this observation to biological fluids, C. neoformans yeasts (1×105) were next treated with undiluted bronchoalveolar lavage fluid (BAL). In contrast to the previous conditions, we were able to detect a small amount of SP-A binding under these conditions (Figure 1B). Our interpretation of these results was that another factor present in BAL may have enabled SP-A to bind to C. neoformans. In the process of considering factors in BAL that might mediate SP-A binding to C. neoformans, immunoglobulins were selected as candidates for binding assays.


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 does not directly bind to encapsulated C. neoformans yeast.(A.) C. neoformans (1×105) were treated with Alexa Flour 488 labeled SP-A (20 µg/ml) for 60 minutes at 37°C. Surfactant protein binding was quantified by flow cytometric analysis. SP-A binding was not detected. (B.) In contrast, C. neoformans (1×105) treated with undiluted BAL exhibited a small amount of SP-A binding. Results are one representative experiment of at least three (A.) or two (B.) experiments performed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0001370-g001: SP-A does not directly bind to encapsulated C. neoformans yeast.(A.) C. neoformans (1×105) were treated with Alexa Flour 488 labeled SP-A (20 µg/ml) for 60 minutes at 37°C. Surfactant protein binding was quantified by flow cytometric analysis. SP-A binding was not detected. (B.) In contrast, C. neoformans (1×105) treated with undiluted BAL exhibited a small amount of SP-A binding. Results are one representative experiment of at least three (A.) or two (B.) experiments performed.
Mentions: Previous studies by Walenkamp et al. and Schelenz et al. showed that in vitro, SP-A binding is restricted to acapsular and minimally encapsulated strains of C. neoformans [10], [11]. To confirm these results, we performed flow cytometry to quantify AF488 labeled SP-A binding to encapsulated C. neoformans yeast (1×105). SP-A binding assays using Escherichia coli HB101 were performed to confirm the binding activity of all SP-A preparations (results not shown). Our results were consistent with those of previous studies; we did not observe SP-A binding to encapsulated H99 C. neoformans yeasts (Figure 1A). To extend this observation to biological fluids, C. neoformans yeasts (1×105) were next treated with undiluted bronchoalveolar lavage fluid (BAL). In contrast to the previous conditions, we were able to detect a small amount of SP-A binding under these conditions (Figure 1B). Our interpretation of these results was that another factor present in BAL may have enabled SP-A to bind to C. neoformans. In the process of considering factors in BAL that might mediate SP-A binding to C. neoformans, immunoglobulins were selected as candidates for binding assays.

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