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Alveolar epithelial type II cells activate alveolar macrophages and mitigate P. Aeruginosa infection.

Kannan S, Huang H, Seeger D, Audet A, Chen Y, Huang C, Gao H, Li S, Wu M - PLoS ONE (2009)

Bottom Line: The ability of phagocytosis and superoxide release by AM was reduced by MCP-1 neutralizing antibodies.Mechanistically, we found that Lyn mediated NFkappaB activation led to increased gene expression and secretion of MCP-1.Collectively, our data indicate that AECII may serve as an immune booster for fighting bacterial infections, particularly in severe immunocompromised conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, University of North Dakota, Grand Forks, North Dakota, USA.

ABSTRACT
Although alveolar epithelial type II cells (AECII) perform substantial roles in the maintenance of alveolar integrity, the extent of their contributions to immune defense is poorly understood. Here, we demonstrate that AECII activates alveolar macrophages (AM) functions, such as phagocytosis using a conditioned medium from AECII infected by P. aeruginosa. AECII-derived chemokine MCP-1, a monocyte chemoattractant protein, was identified as a main factor in enhancing AM function. We proposed that the enhanced immune potency of AECII may play a critical role in alleviation of bacterial propagation and pneumonia. The ability of phagocytosis and superoxide release by AM was reduced by MCP-1 neutralizing antibodies. Furthermore, MCP-1(-/-) mice showed an increased bacterial burden under PAO1 and PAK infection vs. wt littermates. AM from MCP-1(-/-) mice also demonstrated less superoxide and impaired phagocytosis over the controls. In addition, AECII conditioned medium increased the host defense of airway in MCP-1(-/-) mice through the activation of AM function. Mechanistically, we found that Lyn mediated NFkappaB activation led to increased gene expression and secretion of MCP-1. Consequently Lyn(-/-) mice had reduced MCP-1 secretion and resulted in a decrease in superoxide and phagocytosis by AM. Collectively, our data indicate that AECII may serve as an immune booster for fighting bacterial infections, particularly in severe immunocompromised conditions.

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MCP-1−/− mice demonstrated functional involvement with P. aeruginosa infection.(A) MCP-1−/− mice showed more severe infection by P. aeruginosa (strains PAO1 and PAK) with an increase in bacterial burdens. Data were derived from a group of 5 infected and control mice (same in the figure). (B) Superoxide production was significantly altered in AM from MCP-1−/− mice following infection identified by NBT assay. (C) A significant increase in apoptotic cell death was observed in MCP-1−/− mice by bacterial infection. The data identified the loss of mitochondrial potential in MCP knockout mice, indicating increased cell apoptosis. (D) An increase opsonic phagocytosis with E. coli particles was found in AM derived from MCP-1−/− mice following infection. (E) An increase in inflammatory chemokine MIP-2α in the MCP-1−/− mice after PAO1 infection. The mRNA expression is shown in an agarose gel using semi-quantitative RT-PCR. (F) Conditioned medium partially restored the immune defense against P. aeruginosa infection in MCP-1−/− mice. Statistical analysis was as above. The results are representative of two experiments.
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pone-0004891-g004: MCP-1−/− mice demonstrated functional involvement with P. aeruginosa infection.(A) MCP-1−/− mice showed more severe infection by P. aeruginosa (strains PAO1 and PAK) with an increase in bacterial burdens. Data were derived from a group of 5 infected and control mice (same in the figure). (B) Superoxide production was significantly altered in AM from MCP-1−/− mice following infection identified by NBT assay. (C) A significant increase in apoptotic cell death was observed in MCP-1−/− mice by bacterial infection. The data identified the loss of mitochondrial potential in MCP knockout mice, indicating increased cell apoptosis. (D) An increase opsonic phagocytosis with E. coli particles was found in AM derived from MCP-1−/− mice following infection. (E) An increase in inflammatory chemokine MIP-2α in the MCP-1−/− mice after PAO1 infection. The mRNA expression is shown in an agarose gel using semi-quantitative RT-PCR. (F) Conditioned medium partially restored the immune defense against P. aeruginosa infection in MCP-1−/− mice. Statistical analysis was as above. The results are representative of two experiments.

Mentions: To further determine the role of MCP-1 as an immune stimulator, MCP-1 deficient mice (MCP−/− mice) were used to study MCP-1 effects on AM immune function and physiological role during P. aeruginosa infection. This can also distinguish the relative contributions of MCP-1 to immune defense against P. aeruginosa infection. We found that MCP-1−/− mice showed increased bacterial burden in the lung (Figure 4A). A significant decrease in the superoxide production in AM was also noted (Figure 4B). Furthermore, the lung from MCP-1−/− mice showed increased lung cell death (showing decreased mitochondrial potential) following infection by P. aeruginosa (Figure 4C). Lung injury was also present as wet/dry ratio was increased by infection in the mice (data not shown). We also showed that isolated AM from MCP-1−/− mice after bacterial infection had increased ability to phagocytose opsonized-E coli particles (Figure 4D), indicating that the AM have not been saturated in uptaking bacteria (probably due to reduced migration) during in vivo infection. Interestingly, we noted that the lung injury is correlated with the increase in a number of pro-inflammatory factors such as MIP-2α (but probably also due to the loss of MCP-1) than the wild-type control (Figure 4E). Also, there was an increased neutrophil infiltration in the BAL (not shown). These data suggest that MCP-1 may be crucial in maintaining a fine balance between pro-inflammatory and anti-inflammatory cytokines, which is important for combating bacterial invasion as well as minimizing acute lung injury. Also, we instilled the conditioned medium into MCP-1−/− mouse lungs, which increased the host defense compared to the control medium (Figure 4F). These data critically confirm that MCP-1 is a potent immune regulator and inflammation controller in the airway spaces.


Alveolar epithelial type II cells activate alveolar macrophages and mitigate P. Aeruginosa infection.

Kannan S, Huang H, Seeger D, Audet A, Chen Y, Huang C, Gao H, Li S, Wu M - PLoS ONE (2009)

MCP-1−/− mice demonstrated functional involvement with P. aeruginosa infection.(A) MCP-1−/− mice showed more severe infection by P. aeruginosa (strains PAO1 and PAK) with an increase in bacterial burdens. Data were derived from a group of 5 infected and control mice (same in the figure). (B) Superoxide production was significantly altered in AM from MCP-1−/− mice following infection identified by NBT assay. (C) A significant increase in apoptotic cell death was observed in MCP-1−/− mice by bacterial infection. The data identified the loss of mitochondrial potential in MCP knockout mice, indicating increased cell apoptosis. (D) An increase opsonic phagocytosis with E. coli particles was found in AM derived from MCP-1−/− mice following infection. (E) An increase in inflammatory chemokine MIP-2α in the MCP-1−/− mice after PAO1 infection. The mRNA expression is shown in an agarose gel using semi-quantitative RT-PCR. (F) Conditioned medium partially restored the immune defense against P. aeruginosa infection in MCP-1−/− mice. Statistical analysis was as above. The results are representative of two experiments.
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Related In: Results  -  Collection

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pone-0004891-g004: MCP-1−/− mice demonstrated functional involvement with P. aeruginosa infection.(A) MCP-1−/− mice showed more severe infection by P. aeruginosa (strains PAO1 and PAK) with an increase in bacterial burdens. Data were derived from a group of 5 infected and control mice (same in the figure). (B) Superoxide production was significantly altered in AM from MCP-1−/− mice following infection identified by NBT assay. (C) A significant increase in apoptotic cell death was observed in MCP-1−/− mice by bacterial infection. The data identified the loss of mitochondrial potential in MCP knockout mice, indicating increased cell apoptosis. (D) An increase opsonic phagocytosis with E. coli particles was found in AM derived from MCP-1−/− mice following infection. (E) An increase in inflammatory chemokine MIP-2α in the MCP-1−/− mice after PAO1 infection. The mRNA expression is shown in an agarose gel using semi-quantitative RT-PCR. (F) Conditioned medium partially restored the immune defense against P. aeruginosa infection in MCP-1−/− mice. Statistical analysis was as above. The results are representative of two experiments.
Mentions: To further determine the role of MCP-1 as an immune stimulator, MCP-1 deficient mice (MCP−/− mice) were used to study MCP-1 effects on AM immune function and physiological role during P. aeruginosa infection. This can also distinguish the relative contributions of MCP-1 to immune defense against P. aeruginosa infection. We found that MCP-1−/− mice showed increased bacterial burden in the lung (Figure 4A). A significant decrease in the superoxide production in AM was also noted (Figure 4B). Furthermore, the lung from MCP-1−/− mice showed increased lung cell death (showing decreased mitochondrial potential) following infection by P. aeruginosa (Figure 4C). Lung injury was also present as wet/dry ratio was increased by infection in the mice (data not shown). We also showed that isolated AM from MCP-1−/− mice after bacterial infection had increased ability to phagocytose opsonized-E coli particles (Figure 4D), indicating that the AM have not been saturated in uptaking bacteria (probably due to reduced migration) during in vivo infection. Interestingly, we noted that the lung injury is correlated with the increase in a number of pro-inflammatory factors such as MIP-2α (but probably also due to the loss of MCP-1) than the wild-type control (Figure 4E). Also, there was an increased neutrophil infiltration in the BAL (not shown). These data suggest that MCP-1 may be crucial in maintaining a fine balance between pro-inflammatory and anti-inflammatory cytokines, which is important for combating bacterial invasion as well as minimizing acute lung injury. Also, we instilled the conditioned medium into MCP-1−/− mouse lungs, which increased the host defense compared to the control medium (Figure 4F). These data critically confirm that MCP-1 is a potent immune regulator and inflammation controller in the airway spaces.

Bottom Line: The ability of phagocytosis and superoxide release by AM was reduced by MCP-1 neutralizing antibodies.Mechanistically, we found that Lyn mediated NFkappaB activation led to increased gene expression and secretion of MCP-1.Collectively, our data indicate that AECII may serve as an immune booster for fighting bacterial infections, particularly in severe immunocompromised conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, University of North Dakota, Grand Forks, North Dakota, USA.

ABSTRACT
Although alveolar epithelial type II cells (AECII) perform substantial roles in the maintenance of alveolar integrity, the extent of their contributions to immune defense is poorly understood. Here, we demonstrate that AECII activates alveolar macrophages (AM) functions, such as phagocytosis using a conditioned medium from AECII infected by P. aeruginosa. AECII-derived chemokine MCP-1, a monocyte chemoattractant protein, was identified as a main factor in enhancing AM function. We proposed that the enhanced immune potency of AECII may play a critical role in alleviation of bacterial propagation and pneumonia. The ability of phagocytosis and superoxide release by AM was reduced by MCP-1 neutralizing antibodies. Furthermore, MCP-1(-/-) mice showed an increased bacterial burden under PAO1 and PAK infection vs. wt littermates. AM from MCP-1(-/-) mice also demonstrated less superoxide and impaired phagocytosis over the controls. In addition, AECII conditioned medium increased the host defense of airway in MCP-1(-/-) mice through the activation of AM function. Mechanistically, we found that Lyn mediated NFkappaB activation led to increased gene expression and secretion of MCP-1. Consequently Lyn(-/-) mice had reduced MCP-1 secretion and resulted in a decrease in superoxide and phagocytosis by AM. Collectively, our data indicate that AECII may serve as an immune booster for fighting bacterial infections, particularly in severe immunocompromised conditions.

Show MeSH
Related in: MedlinePlus