*Bronchial epithelial cells represent the first line of defense against invading airborne pathogens. They are important contributors to innate mucosal immunity and provide a variety of antimicrobial effectors. However, mucosal surfaces are prone to contact with pathogenic, as well as nonpathogenic microbes, and therefore, immune recognition principles have to be tightly controlled to avoid uncontrolled permanent activation. TLRs have been shown to recognize conserved microbial patterns and to mediate inducible activation of innate immunity. Our experiments demonstrate that bronchial epithelial cells express functional TLR1-6 and TLR9 and thus make use of a common principle of professional innate immune cells. Although it was observed that TLR2 ligands dependent on heterodimeric signaling either with TLR1 or TLR6 were functional, other ligands like lipoteichoic acid were not. Additionally, it was found that bronchial epithelial cells could be stimulated only marginally by Gram-positive bacteria bearing known TLR2 ligands while Gram-negative bacteria were easily recognized. This correlated with low expression of TLR2 and the missing expression of the coreceptor CD36. Transgenic expression of both receptors restored responsiveness to the complete set of TLR2 ligands and Staphylococcus aureus. Additional gene-array experiments confirmed hyporesponsiveness to this bacterium while Pseudomonas aeruginosa and respiratory syncytial virus induced common, as well as pathogen-specific, sets of genes. The findings indicate that bronchial epithelium regulates its sensitivity to recognize microbes by managing receptor expression levels. This could serve the special needs of controlled microbial recognition in mucosal compartments.
Immune defense capacity differs between men and women. Whereas men are more prone to infection and sepsis, women more commonly develop autoimmune diseases. We investigated the difference in cytokine secretion between males and females in response to different immune stimuli. Whole blood from 154 healthy volunteers (age 24 +/- 5.2; 82 females, 72 males) was collected within 2 h on 2 consecutive days. Blood from males produced significantly more tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, and IL-8 than blood from females in response to a high concentration of either lipopolysaccharide (LPS) or lipoteichoic acid (LTA), whereas IL-10 and interferon-gamma (IFN-gamma) secretion did not differ. Normalization of cytokine measurement to individual monocyte counts cancelled these differences for all parameters except TNF-alpha. Stimulation with a lower concentration of LPS (100 pg/mL) produced even stronger differences in cytokine release, which were not cancelled by normalization to the producing cells. The coefficients of variation (CV) of the LPS-induced and LTA-induced cytokine responses were higher in blood from women than men for all parameters and stimuli measured. Thus, the stronger innate immune response of males in comparison to females appears to stem not only from a difference in monocyte counts but also from the steepness of the response curve.
The heterozygous Asp299Gly mutation of the toll-like receptor (TLR) 4, the key receptor for lipopolysaccharide (LPS), has been associated with attenuated inflammatory responses. When 160 healthy volunteers (9% heterozygous and 0.6% homozygous) were genotyped and their LPS-inducible cytokine release was assessed in an ex vivo whole blood test, the responses of heterozygotes did not differ significantly from those of wild-type carriers for any of the cytokines (tumor necrosis factor-alpha, interleukin [IL]-1beta, IL-6, interferon-gamma, and granulocyte colony-stimulating factor) or eicosanoids measured or for serum cytokines and C-reactive protein. Ten heterozygous subjects and 12 wild-type control subjects responded similarly to a graded series of LPS and Escherichia coli concentrations, excluding the possibility that allele-specific differences are evident only at low stimulus concentrations or in response to whole pathogens. These data demonstrate that the heterozygous Asp299Gly polymorphism does not exhibit a functional defect in cytokine release after the stimulation of blood monocytes.
While transfection of tlr2 conveyed responsiveness to lipoteichoic acid (LTA), the Arg753Gln polymorphic gene could not. LTA induced a stronger chemokine and anti-inflammatory response than lipopolysaccharides did. Blood from heterozygous polymorphic and wild-type donors reacted uniformly to LTA and Staphylococcus aureus. Thus, one functional allele for Toll-like receptor 2 suffices for full cytokine response.Since the discovery of the Toll-like receptors (TLRs) as crucial receptors recognizing microbial components and alerting the immune system (reviewed in reference 4), healthy and patient populations have been screened for polymorphisms in their tlr2 and tlr4 genes to determine whether such polymorphisms may be risk factors for bacterial infections. Results obtained up to now have been inconclusive, as only a few carriers of polymorphisms have been identified in small populations and functional assays of the patients' ability to respond to bacterial stimuli were often not performed. We genotyped 160 volunteers for the Asp299Gly polymorphism of tlr4 and assessed their basal and inducible cytokine release levels. Although the heterozygous Asp299Gly polymorphism has been reported to be a defective polymorphism, our data (10) and a study performed by Erridge et al. (1) do not support any functional consequence of this polymorphism on the inflammatory response.A mutation screen of 110 healthy volunteers found only one missense mutation of tlr2 (Arg753Gln) in the open reading frame (5). Functional studies of that polymorphism in transfected cells showed a diminished response to peptides derived from Borrelia burgdorferi and Treponema pallidum; however, the incidence of the polymorphism was not higher in a septicshock population than in healthy volunteers (5). The immunostimulatory principles of borreliae and treponemata are not yet clearly defined. We have developed an isolation procedure for lipoteichoic acid (LTA) from gram-positive bacteria which yields highly pure, bioactive LTA (6) that requires TLR2 for signaling (3). LTA from Staphylococcus aureus was synthesized chemically on the basis of the proposed structure and found to have biological activity comparable to that of purified natural LTA (8). Thus, we employed LTA from S. aureus, Bacillus subtilis, and live S. aureus to investigate the influence of the Arg753Gln TLR2 polymorphism on inflammatory capacity.293T cells transfected with wild-type TLR2 as previously described (5) responded to stimulation with LTA from S. aureus (6 h at 1.5 g/ml) with increased NF-B-luciferase reporter activity (Fig. 1). This significant increase above basal activity was absent in cells transfected with the Arg753Gln polymorphism, indicating that the polymorphism results in a nonfunctional protein.To be able to compare the cytokine induction potency of LTA from S. aureus (prepared in-house as described previously [6,7], without endotoxin contamination, as indicated by negative Limulus amoebocyte lysate assay [QCL-1000; Charles River Endosafe] results) with that of lipopolysacch...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.