Toll-like receptor 2 ligands activate human basophils for both IgE-dependent and IgE-independent secretion.
BACKGROUND
Toll-like receptor (TLR) molecules play a critical role in directing the course of acquired immunity, including that associated with allergic disease, by recognizing specific microbial products that activate immune cells for effector functions.


OBJECTIVE
We investigated whether human basophils express 2 such molecules (TLR2 and TLR4), and assessed whether putative ligands for these receptors activate nuclear factor kappaB (NFkappaB) and modulate mediator release and cytokine secretion either alone or in response to stimulation.


METHODS
Toll-like receptor expression was assessed by using RT-PCR and flow cytometry. Immunoblotting detected nuclear NFkappaB. Automated fluorometry, RIA, and ELISA detected concurrent changes in histamine, leukotriene C 4 , and cytokine, respectively, after culture with specific ligands.


RESULTS
mRNA and protein for TLR2 and TLR4 were detected in basophils. However, in assessing nuclear localization of NFkappaB as a measure of functional receptor responses, basophils selectively reacted only to peptidoglycan, a TLR2 ligand, and not to LPS, a TLR4 ligand. Likewise, basophils secreted both IL-4 and IL-13 in direct response to peptidoglycan but not to LPS. Although neither ligand induced histamine or leukotriene C 4 release, several TLR2-specific ligands augmented the secretion of these mediators (and cytokine) in response to IgE-dependent activation and of IL-13 in response to IgE-independent stimulation. Finally, a selective inhibitor of NFkappaB did not prevent these enhancing effects mediated by TLR2 ligands.


CONCLUSIONS
These data suggest that innate immune responses mediated through TLR2 play a role in augmenting allergic reactions, in part by modulating basophil cytokine secretion and mediator release independently of NFkappaB activation.
Bieneman
Anja P
AP
Johns Hopkins Asthma and Allergy Center, Department of Medicine, Johns Hopkins University, Baltimore, MD 21224, USA.
Chichester
Kristin L
KL
Chen
Yi-Hsing
YH
Schroeder
John T
JT
D001491:Basophils / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D006801:Humans; D007073:Immunoglobulin E / Q000502:physiology*; D018793:Interleukin-13 / Q000378:metabolism; D015847:Interleukin-4 / Q000096:biosynthesis; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010457:Peptidoglycan / Q000494:pharmacology*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
D016207:Cytokines; D018793:Interleukin-13; D008024:Ligands; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D010457:Peptidoglycan; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015847:Interleukin-4; D007073:Immunoglobulin E