Toll-like receptor-4 signaling mediates pulmonary neutrophil sequestration in response to gram-positive bacterial enterotoxin.
BACKGROUND
Toll-like receptors (TLRs) serve as mediators of innate immune responses to pathogen-associated molecular patterns (PAMPs) which include lipopolysaccharide (LPS) and staphylococcal enterotoxin B (SEB). TLR-4 is thought to act as the primary effector of LPS recognition and TLR-2 is thought to mediate responses to Gram-positive bacterial proteins. Chemokines such as macrophage inflammatory protein (MIP-2) are peptides that are responsible for lung neutrophil (PMN) sequestration following an infectious or inflammatory insult. Given the Gram-positive origin of SEB, we hypothesized that mice with altered TLR-4 signaling would exhibit no difference in lung PMN sequestration following SEB when compared to wild-type mice.


METHODS
Wild-type and TLR-4 mutant mice were administered intratracheal saline, LPS (Escherichia coli 0.1 mg/kg), or SEB (1 mg/kg). After 24 h, lung PMN accumulation was determined by myeloperoxidase (MPO) assay and bronchoalveolar lavage fluid cell count (BALfcc). Total lung and BALf MIP-2 was measured by enzyme-linked immunosorbent assay.


RESULTS
There was an increase in lung PMN accumulation (by both MPO and BALfcc) and MIP-2 following LPS and SEB in wild-type mice compared to saline-treated controls. In contrast, TLR-4 mice failed to exhibit an increase in lung MIP-2 or PMN accumulation following either LPS or SEB compared to wild-type mice.


CONCLUSIONS
TLR-4 mutant mice are unresponsive to intratracheal LPS. SEB elicited an increase in lung MIP-2 and PMN accumulation in wild-type mice. However, TLR-4 mutant mice were protected from this process. This suggests that TLR-4 signaling may mediate the responses to other PAMPs in addition to LPS.
Calkins
Casey M
CM
Department of Surgery, University of Colorado Health Sciences Center and Veterans Affairs Hospital, Denver, USA.
Barsness
Katherine
K
Bensard
Denis D
DD
Vasquez-Torres
Andres
A
Raeburn
Christopher D
CD
Meng
Xianzhong
X
McIntyre
Robert C
RC
D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D054426:Chemokine CXCL2; D029721:Drosophila Proteins; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli; D008070:Lipopolysaccharides / Q000008:administration & dosage / Q000494:pharmacology*; D008168:Lung / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D015846:Monokines / Q000032:analysis / Q000378:metabolism; D009504:Neutrophils / Q000473:pathology*; D009195:Peroxidase / Q000032:analysis; D011650:Pulmonary Alveoli / Q000473:pathology; D011956:Receptors, Cell Surface / Q000502:physiology*; D015398:Signal Transduction; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014132:Trachea
D054426:Chemokine CXCL2; D029721:Drosophila Proteins; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D015846:Monokines; D011956:Receptors, Cell Surface; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D009195:Peroxidase