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The macrophage scavenger receptor type A is expressed by activated macrophages and protects the host against lethal endotoxic shock.

Haworth R, Platt N, Keshav S, Hughes D, Darley E, Suzuki H, Kurihara Y, Kodama T, Gordon S - J. Exp. Med. (1997)

Bottom Line: We show that activated Mphi express SR-A and that this molecule is functional in assays of adhesion and endocytic uptake.Thus SR-A, expressed by activated Mphi, plays a protective role in host defense by scavenging LPS as well as by reducing the release by activated Mphi of proinflammatory cytokines.Modulation of SR-A may provide a novel therapeutic approach to control endotoxic shock.

View Article: PubMed Central - PubMed

Affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.

ABSTRACT
During gram-negative bacterial infections, lipopolysaccharide (LPS) stimulates primed macrophages (Mphi) to release inflammatory mediators such as tumor necrosis factor (TNF)-alpha, which can cause hypotension, organ failure, and often death. Several different receptors on Mphi have been shown to bind LPS, including the type A scavenger receptor (SR-A). This receptor is able to bind a broad range of polyanionic ligands such as modified lipoproteins and lipoteichoic acid of gram-positive bacteria, which suggests that SR-A plays a role in host defense. In this study, we used mice lacking the SR-A (SRKO) to investigate the role of SR-A in acquired immunity using a viable bacillus Calmette Guérin (BCG) infection model. We show that activated Mphi express SR-A and that this molecule is functional in assays of adhesion and endocytic uptake. After BCG infection, SRKO mice are able to recruit Mphi to sites of granuloma formation where they become activated and restrict BCG replication. However, infected mice lacking the SR-A are more susceptible to endotoxic shock and produce more TNF-alpha and interleukin-6 in response to LPS. In addition, we show that an antibody which blocks TNF-alpha activity reduces LPS-induced mortality in these mice. Thus SR-A, expressed by activated Mphi, plays a protective role in host defense by scavenging LPS as well as by reducing the release by activated Mphi of proinflammatory cytokines. Modulation of SR-A may provide a novel therapeutic approach to control endotoxic shock.

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Functional phenotype of BCG-activated SRKO and wild-type Mφ. (A) Adhesion of activated Mφ to FBS-coated TCP. Cells were  plated at 3 × 105 macrophages/well of a 96-well plate in the presence of  various mAbs and/or EDTA. BCG-recruited peritoneal cells from SRKO  and wild-type (129) mice show similar adhesion in medium (R10) alone,  but in the presence of both EDTA and isotype-matched control mAb  (T1), adhesion of SRKO Mφ is completely inhibited (compare with  wild-type 129), showing that SR-A accounts for all EDTA-resistant adhesion. Addition of 2F8 mAb and EDTA is required to completely inhibit the remaining adhesion of 129 activated Mφ. Adhesion is represented as the percentage of that obtained in medium alone, where 100%  represents an absorbance (OD) at 450 nm of 0.15. Results (mean ± SD)  are derived from a single experiment (n = 4) and are representative of  three similar experiments. (B) The uptake of DiIAcLDL by SRKO and  wild-type (129) BCG-recruited peritoneal cells. Cells were harvested as in  A and the uptake of DiIAcLDL measured as described in Materials and  Methods. SRKO endocytose only 40% of the DiIAcLDL taken up by  129 cells. 2F8 mAb reduces the uptake by 129 cells to that of SRKO cells,  whereas an isotype-matched control Ab (CP) has no effect. Uptake of DiIAcLDL is expressed by units of fluorescence (mean ± SD) of four replicate wells and is relative to a blank well of cells without the addition of  DiIAcLDL. Results are derived from a single experiment and are representative of at least three similar experiments. Uptake of DiIAcLDL by  129 Mφ in the presence of medium or CP is significantly greater than uptake by SRKO Mφ (P <0.005).
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Figure 2: Functional phenotype of BCG-activated SRKO and wild-type Mφ. (A) Adhesion of activated Mφ to FBS-coated TCP. Cells were plated at 3 × 105 macrophages/well of a 96-well plate in the presence of various mAbs and/or EDTA. BCG-recruited peritoneal cells from SRKO and wild-type (129) mice show similar adhesion in medium (R10) alone, but in the presence of both EDTA and isotype-matched control mAb (T1), adhesion of SRKO Mφ is completely inhibited (compare with wild-type 129), showing that SR-A accounts for all EDTA-resistant adhesion. Addition of 2F8 mAb and EDTA is required to completely inhibit the remaining adhesion of 129 activated Mφ. Adhesion is represented as the percentage of that obtained in medium alone, where 100% represents an absorbance (OD) at 450 nm of 0.15. Results (mean ± SD) are derived from a single experiment (n = 4) and are representative of three similar experiments. (B) The uptake of DiIAcLDL by SRKO and wild-type (129) BCG-recruited peritoneal cells. Cells were harvested as in A and the uptake of DiIAcLDL measured as described in Materials and Methods. SRKO endocytose only 40% of the DiIAcLDL taken up by 129 cells. 2F8 mAb reduces the uptake by 129 cells to that of SRKO cells, whereas an isotype-matched control Ab (CP) has no effect. Uptake of DiIAcLDL is expressed by units of fluorescence (mean ± SD) of four replicate wells and is relative to a blank well of cells without the addition of DiIAcLDL. Results are derived from a single experiment and are representative of at least three similar experiments. Uptake of DiIAcLDL by 129 Mφ in the presence of medium or CP is significantly greater than uptake by SRKO Mφ (P <0.005).

Mentions: Previous work has demonstrated a role for SR-A in mediating cation-independent adhesion of thioglycollate broth– elicited peritoneal Mφ (29) to TCP in the presence of serum (17). To examine whether activated Mφ from the SRKO mouse showed an altered adhesion phenotype in vitro, BCG-elicited peritoneal cells were harvested and their adhesion to TCP was examined in the presence of serum (Fig. 2 A). In the presence of medium (R10) alone or control antibody (anti–Thy-1), the adhesion of wild-type and SRKO cells was identical. However, in the presence of EDTA, which chelates divalent cations, significant adhesion of the wild-type cells remained, whereas adhesion of the SRKO cells was completely inhibited. In the additional presence of the anti–SR-A blocking mAb 2F8, wild-type adhesion was further reduced to the level of the SRKO cells.


The macrophage scavenger receptor type A is expressed by activated macrophages and protects the host against lethal endotoxic shock.

Haworth R, Platt N, Keshav S, Hughes D, Darley E, Suzuki H, Kurihara Y, Kodama T, Gordon S - J. Exp. Med. (1997)

Functional phenotype of BCG-activated SRKO and wild-type Mφ. (A) Adhesion of activated Mφ to FBS-coated TCP. Cells were  plated at 3 × 105 macrophages/well of a 96-well plate in the presence of  various mAbs and/or EDTA. BCG-recruited peritoneal cells from SRKO  and wild-type (129) mice show similar adhesion in medium (R10) alone,  but in the presence of both EDTA and isotype-matched control mAb  (T1), adhesion of SRKO Mφ is completely inhibited (compare with  wild-type 129), showing that SR-A accounts for all EDTA-resistant adhesion. Addition of 2F8 mAb and EDTA is required to completely inhibit the remaining adhesion of 129 activated Mφ. Adhesion is represented as the percentage of that obtained in medium alone, where 100%  represents an absorbance (OD) at 450 nm of 0.15. Results (mean ± SD)  are derived from a single experiment (n = 4) and are representative of  three similar experiments. (B) The uptake of DiIAcLDL by SRKO and  wild-type (129) BCG-recruited peritoneal cells. Cells were harvested as in  A and the uptake of DiIAcLDL measured as described in Materials and  Methods. SRKO endocytose only 40% of the DiIAcLDL taken up by  129 cells. 2F8 mAb reduces the uptake by 129 cells to that of SRKO cells,  whereas an isotype-matched control Ab (CP) has no effect. Uptake of DiIAcLDL is expressed by units of fluorescence (mean ± SD) of four replicate wells and is relative to a blank well of cells without the addition of  DiIAcLDL. Results are derived from a single experiment and are representative of at least three similar experiments. Uptake of DiIAcLDL by  129 Mφ in the presence of medium or CP is significantly greater than uptake by SRKO Mφ (P <0.005).
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Figure 2: Functional phenotype of BCG-activated SRKO and wild-type Mφ. (A) Adhesion of activated Mφ to FBS-coated TCP. Cells were plated at 3 × 105 macrophages/well of a 96-well plate in the presence of various mAbs and/or EDTA. BCG-recruited peritoneal cells from SRKO and wild-type (129) mice show similar adhesion in medium (R10) alone, but in the presence of both EDTA and isotype-matched control mAb (T1), adhesion of SRKO Mφ is completely inhibited (compare with wild-type 129), showing that SR-A accounts for all EDTA-resistant adhesion. Addition of 2F8 mAb and EDTA is required to completely inhibit the remaining adhesion of 129 activated Mφ. Adhesion is represented as the percentage of that obtained in medium alone, where 100% represents an absorbance (OD) at 450 nm of 0.15. Results (mean ± SD) are derived from a single experiment (n = 4) and are representative of three similar experiments. (B) The uptake of DiIAcLDL by SRKO and wild-type (129) BCG-recruited peritoneal cells. Cells were harvested as in A and the uptake of DiIAcLDL measured as described in Materials and Methods. SRKO endocytose only 40% of the DiIAcLDL taken up by 129 cells. 2F8 mAb reduces the uptake by 129 cells to that of SRKO cells, whereas an isotype-matched control Ab (CP) has no effect. Uptake of DiIAcLDL is expressed by units of fluorescence (mean ± SD) of four replicate wells and is relative to a blank well of cells without the addition of DiIAcLDL. Results are derived from a single experiment and are representative of at least three similar experiments. Uptake of DiIAcLDL by 129 Mφ in the presence of medium or CP is significantly greater than uptake by SRKO Mφ (P <0.005).
Mentions: Previous work has demonstrated a role for SR-A in mediating cation-independent adhesion of thioglycollate broth– elicited peritoneal Mφ (29) to TCP in the presence of serum (17). To examine whether activated Mφ from the SRKO mouse showed an altered adhesion phenotype in vitro, BCG-elicited peritoneal cells were harvested and their adhesion to TCP was examined in the presence of serum (Fig. 2 A). In the presence of medium (R10) alone or control antibody (anti–Thy-1), the adhesion of wild-type and SRKO cells was identical. However, in the presence of EDTA, which chelates divalent cations, significant adhesion of the wild-type cells remained, whereas adhesion of the SRKO cells was completely inhibited. In the additional presence of the anti–SR-A blocking mAb 2F8, wild-type adhesion was further reduced to the level of the SRKO cells.

Bottom Line: We show that activated Mphi express SR-A and that this molecule is functional in assays of adhesion and endocytic uptake.Thus SR-A, expressed by activated Mphi, plays a protective role in host defense by scavenging LPS as well as by reducing the release by activated Mphi of proinflammatory cytokines.Modulation of SR-A may provide a novel therapeutic approach to control endotoxic shock.

View Article: PubMed Central - PubMed

Affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.

ABSTRACT
During gram-negative bacterial infections, lipopolysaccharide (LPS) stimulates primed macrophages (Mphi) to release inflammatory mediators such as tumor necrosis factor (TNF)-alpha, which can cause hypotension, organ failure, and often death. Several different receptors on Mphi have been shown to bind LPS, including the type A scavenger receptor (SR-A). This receptor is able to bind a broad range of polyanionic ligands such as modified lipoproteins and lipoteichoic acid of gram-positive bacteria, which suggests that SR-A plays a role in host defense. In this study, we used mice lacking the SR-A (SRKO) to investigate the role of SR-A in acquired immunity using a viable bacillus Calmette Guérin (BCG) infection model. We show that activated Mphi express SR-A and that this molecule is functional in assays of adhesion and endocytic uptake. After BCG infection, SRKO mice are able to recruit Mphi to sites of granuloma formation where they become activated and restrict BCG replication. However, infected mice lacking the SR-A are more susceptible to endotoxic shock and produce more TNF-alpha and interleukin-6 in response to LPS. In addition, we show that an antibody which blocks TNF-alpha activity reduces LPS-induced mortality in these mice. Thus SR-A, expressed by activated Mphi, plays a protective role in host defense by scavenging LPS as well as by reducing the release by activated Mphi of proinflammatory cytokines. Modulation of SR-A may provide a novel therapeutic approach to control endotoxic shock.

Show MeSH
Related in: MedlinePlus