Innate immune responses of the airway epithelium

Barrier epithelia, especially airway epithelial cells, are persistently exposed to micro-organisms and environmental factors. To protect the host from these microbial challenges, many immune strategies have evolved. The airway epithelium participates in the critical innate immune response through the secretion of immune effectors such as mucin, antimicrobial peptides (AMP), and reactive oxygen species (ROS) to entrap or kill invading microbes. In addition, airway epithelial cells can act as mediators connecting innate and adaptive immunity by producing various cytokines and chemokines. Here, we present an overview of the role of mucosal immunity in airway epithelium, emphasizing the framework of bacterial and viral infections along with regulatory mechanisms of immune effectors in human cells and selected animal models. We also describe pathophysiological roles for immune effectors in human airway disease.     

白念珠菌ALS3、SSA1基因表达在念珠菌性阴道炎免疫机制中的作用

目的探讨白念珠菌ALS3、SSA1基因缺失对阴道上皮细胞激发免疫反应的作用。方法培养白念珠菌野生株及ALS3、SSA1基因敲除株(SC5314、Δals3、Δssa1),对其进行形态测定。按不同MOI感染人阴道上皮细胞系VK2/E6E7细胞,通过台盼蓝染色观察和乳酸脱氢酶(LDH)活性检测,评价不同MOI白念珠菌对上皮细胞的损伤作用;使用酶联免疫吸附试验(ELISA)评估感染过程中炎性细胞因子及趋化因子在共培养上清中的差异。结果 ALS3基因的缺失对白念珠菌芽管长度影响差异无统计学意义,而SSA1基因的缺失与其他两个菌株相比芽管长度减少约30%～40%(P<0.001)。台盼蓝染色观察及LDH测定发现,3株菌在感染上皮细胞时,其细胞损伤能力均与菌载量成正比;与野生型相比,Δssa1突变体在相同比率感染上皮细胞时,细胞损伤能力明显降低,且差异有统计学意义(P<0.05),Δals3突变株影响较小,甚至略微升高。检测炎性细胞因子及趋化因子发现,突变株在诱导上皮细胞产生促炎因子及趋化因子(GM-CSF、G-CSF、IL-1α、IL-8)的能力上明显减弱,差异均有统计学意义(P<0.05)。结论 ALS3和SSA1基因表达在阴道上皮细胞抗白念珠菌感染的局部免疫应答过程中可能起到重要作用,且SSA1基因表达意义更大。     

Stimulation of TLRs by LMW-HA induces self-defense mechanisms in vaginal epithelium

The innate immune system is present throughout the female reproductive tract and functions in synchrony with the adaptive immune system to provide protection in a way that enhances the chances for fetal survival, while protecting against potential pathogens. Recent data show that activation of Toll-like receptor (TLR)2 and 4 by low-molecular weight hyaluronic acid (LMW-HA) in the epidermis induces secretion of the antimicrobial peptide β-defensin 2. In the present work, we show that LMW-HA induces vaginal epithelial cells to release different antimicrobial peptides, via activation of TLR2 and TLR4. Further, we found that LMW-HA favors repair of vaginal epithelial injury, involving TLR2 and TLR4, and independently from its classical receptor CD44. This wound-healing activity of LMW-HA is dependent from an Akt/phosphatidylinositol 3 kinase pathway. Therefore, these findings suggest that the vaginal epithelium is more than a simple physical barrier to protect against invading pathogens: on the contrary, this surface acts as efficient player of innate host defense, which may modulate its antimicrobial properties and injury restitution activity, following LMW-HA stimulation; this activity may furnish an additional protective activity to this body compartment, highly and constantly exposed to microbiota, ameliorating the self-defense of the vaginal epithelium in both basal and pathological conditions.     

TLR9 and RIG-I Signaling in Human Endocervical Epithelial Cells Modulates Inflammatory Responses of Macrophages and Dendritic Cells In Vitro

The innate immune system has evolved to recognize invading pathogens through pattern recognition receptors (PRRs).Among PRRs, Toll like receptors (TLRs 3, 7/8,9) and RIG-I like receptors (RLRs) have been shown to recognize viral components. Mucosal immune responses to viral infections require coordinated actions from epithelial as well as immune cells. In this respect, endocervical epithelial cells (EEC''s) play an important role in initiating innate immune responses via PRRs. It is unknown whether EEC''s can alter immune responses of macrophages and dendritic cells (DC''s) like its counterparts in intestinal and respiratory systems. In this study, we show that endocervical epithelial cells (End1/E6E7) express two key receptors, TLR9 and RIG-I involved in anti-viral immunity. Stimulation of End1/E6E7 cells lead to the activation of NF-κB and increased secretion of pro-inflammatory cytokines, IL-6 and IL-8. Polarized End1/E6E7 cells responded to apical stimulation with ligands of TLR9 and RIG-I, CpG-ODN and Poly(I:C)LL respectively, without compromising End1/E6E7 cell integrity. At steady state, spent medium from End1/E6E7 cells significantly reduced secretion of pro-inflammatory cytokines from LPS treated human primary monocyte derived macrophages (MDMs) and DC:T cell co-cultures. Spent medium from End1/E6E7 cells stimulated with ligands of TLR9/RIG-I restored secretion of pro-inflammatory cytokines as well as enhanced phagocytosis and chemotaxis of monocytic U937 cells. Spent medium from CpG-ODN and Poly(I:C)LL stimulated End1/E6E7 cells showed significant increased secretion of IL-12p70 from DC:T cell co-cultures. The anti-inflammatory effect of spent media of End1/E6E7 cell was observed to be TGF-β dependent. In summary, the results of our study indicate that EEC''s play an indispensable role in modulating anti-viral immune responses at the female lower genital tract.     

Toll-Like Receptor 4 Mediates the Response of Epithelial and Stromal Cells to Lipopolysaccharide in the Endometrium

Background

Ascending infections of the female genital tract with bacteria causes pelvic inflammatory disease (PID), preterm labour and infertility. Lipopolysaccharide (LPS) is the main component of the cell wall of Gram-negative bacteria. Innate immunity relies on the detection of LPS by Toll-like receptor 4 (TLR4) on host cells. Binding of LPS to TLR4 on immune cells stimulates secretion of pro-inflammatory cytokines such as IL-6, chemokines such as CXCL1 and CCL20, and prostaglandin E₂. The present study tested the hypothesis that TLR4 on endometrial epithelial and stromal cells is essential for the innate immune response to LPS in the female genital tract.

Methodology/Principal Findings

Wild type (WT) mice expressed TLR4 in the endometrium. Intrauterine infusion of purified LPS caused pelvic inflammatory disease, with accumulation of granulocytes throughout the endometrium of WT but not Tlr4^−/− mice. Intra-peritoneal infusion of LPS did not cause PID in WT or Tlr4^−/− mice, indicating the importance of TLR4 in the endometrium for the detection of LPS in the female genital tract. Stromal and epithelial cells isolated from the endometrium of WT but not Tlr4^−/− mice, secreted IL-6, CXCL1, CCL20 and prostaglandin E₂ in response to LPS, in a concentration and time dependent manner. Co-culture of combinations of stromal and epithelial cells from WT and Tlr4^−/− mice provided little evidence of stromal-epithelial interactions in the response to LPS.

Conclusions/Significance

The innate immune response to LPS in the female genital tract is dependent on TLR4 on the epithelial and stromal cells of the endometrium.     

Multiple TLRs are expressed in human cholangiocytes and mediate host epithelial defense responses to Cryptosporidium parvum via activation of NF-kappaB

Infection of epithelial cells by Cryptosporidium parvum triggers a variety of host-cell innate and adaptive immune responses including release of cytokines/chemokines and up-regulation of antimicrobial peptides. The mechanisms that trigger these host-cell responses are unclear. Thus, we evaluated the role of TLRs in host-cell responses during C. parvum infection of cultured human biliary epithelia (i.e., cholangiocytes). We found that normal human cholangiocytes express all known TLRs. C. parvum infection of cultured cholangiocytes induces the selective recruitment of TLR2 and TLR4 to the infection sites. Activation of several downstream effectors of TLRs including IL-1R-associated kinase, p-38, and NF-kappaB was detected in infected cells. Transfection of cholangiocytes with dominant-negative mutants of TLR2 and TLR4, as well as the adaptor molecule myeloid differentiation protein 88 (MyD88), inhibited C. parvum-induced activation of IL-1R-associated kinase, p-38, and NF-kappaB. Short-interfering RNA to TLR2, TLR4, and MyD88 also blocked C. parvum-induced NF-kappaB activation. Moreover, C. parvum selectively up-regulated human beta-defensin-2 in directly infected cells, and inhibition of TLR2 and TLR4 signals or NF-kappaB activation were each associated with a reduction of C. parvum-induced human beta-defensin-2 expression. A significantly higher number of parasites were detected in cells transfected with a MyD88 dominant-negative mutant than in the control cells at 48-96 h after initial exposure to parasites, suggesting MyD88-deficient cells were more susceptible to infection. These findings demonstrate that cholangiocytes express a variety of TLRs, and suggest that TLR2 and TLR4 mediate cholangiocyte defense responses to C. parvum via activation of NF-kappaB.     

Microbial patterns signaling via Toll-like receptors 2 and 5 contribute to epithelial repair, growth and survival

Epithelial cells (ECs) continuously interact with microorganisms and detect their presence via different pattern-recognition receptors (PRRs) including Toll-like receptors (TLRs). Ligation of epithelial TLRs by pathogens is usually associated with the induction of pro-inflammatory mediators and antimicrobial factors. In this study, using human airway ECs as a model, we found that detection of microbial patterns via epithelial TLRs directly regulates tissue homeostasis. Staphylococcus aureus (S. aureus) and microbial patterns signaling via TLR2 and TLR5 induce a set of non-immune epithelial responses including cell migration, wound repair, proliferation, and survival of primary and cancerous ECs. Using small interfering RNA (siRNA) gene targeting, receptor-tyrosine kinase microarray and inhibition studies, we determined that TLR and the epidermal growth factor receptor (EGFR) mediate the stimulating effect of microbial patterns on epithelial repair. Microbial patterns signaling via Toll-like receptors 2 and 5 contribute to epithelial repair, growth and survival. This effect is independent of hematopoietic and other cells as well as inflammatory cytokines suggesting that epithelia are able to regulate their integrity in an autonomous non-inflammatory manner by sensing microbes directly via TLRs.     

Differential effects of cytokines and corticosteroids on Toll-like receptor 2 expression and activity in human airway epithelia

Background

The recognition of microbial molecular patterns via Toll-like receptors (TLRs) is critical for mucosal defenses.

Methods

Using well-differentiated primary cultures of human airway epithelia, we investigated the effects of exposure of the cells to cytokines (TNF-α and IFN-γ) and dexamethasone (dex) on responsiveness to the TLR2/TLR1 ligand Pam3CSK4. Production of IL-8, CCL20, and airway surface liquid antimicrobial activity were used as endpoints.

Results

Microarray expression profiling in human airway epithelia revealed that first response cytokines markedly induced TLR2 expression. Real-time PCR confirmed that cytokines (TNF-α and IFN-γ), dexamethasone (dex), or cytokines + dex increased TLR2 mRNA abundance. A synergistic increase was seen with cytokines + dex. To assess TLR2 function, epithelia pre-treated with cytokines ± dex were exposed to the TLR2/TLR1 ligand Pam3CSK4 for 24 hours. While cells pre-treated with cytokines alone exhibited significantly enhanced IL-8 and CCL20 secretion following Pam3CSK4, mean IL-8 and CCL20 release decreased in Pam3CSK4 stimulated cells following cytokines + dex pre-treatment. This marked increase in inflammatory gene expression seen after treatment with cytokines followed by the TLR2 ligand did not correlate well with NF-κB, Stat1, or p38 MAP kinase pathway activation. Cytokines also enhanced TLR2 agonist-induced beta-defensin 2 mRNA expression and increased the antimicrobial activity of airway surface liquid. Dex blocked these effects.

Conclusion

While dex treatment enhanced TLR2 expression, co-administration of dex with cytokines inhibited airway epithelial cell responsiveness to TLR2/TLR1 ligand over cytokines alone. Enhanced functional TLR2 expression following exposure to TNF-α and IFN-γ may serve as a dynamic means to amplify epithelial innate immune responses during infectious or inflammatory pulmonary diseases.     

Toll-like receptor 4 and cytokine expression involved in functional immune response in an originally established porcine intestinal epitheliocyte cell line

To study the immune responses of porcine intestinal epithelial cells to gram-negative bacteria via toll-like receptors (TLRs), originally established porcine intestinal epitheliocyte (PIE) cells were treated with lipopolysaccharide (LPS) or swine-specific enterotoxigenic Escherichia coli (ETEC). Real-time quantitative PCR revealed that PIE cells expressed TLR1-9 and MD-2 mRNAs, preferentially expressed TLR4/MD-2. Immunostaining of PIE cells revealed that TLR4 was precisely expressed in PIE cells at the protein level. PIE cells treated with LPS had up-regulated expression of several TLRs (TLR2, 3, 4, 5 and 8), type 1 helper T (Th1) cytokines (interleukin (IL)-1alpha, IL-1beta, IL-6, IL-15, 18, leukemia inhibitory factor (LIF), and interferon (IFN)-beta), and chemokines (monocyte chemoattractant protein (MCP)-1 and IL-8). ETEC enhanced the expression of TLR2, Th1 type cytokines (IL-1alpha, IL-12p35 and IL-6) and chemokines (MCP-1 and IL-8). These results indicate that PIE induces inflammatory responses by up-regulating Th1 cytokines and chemokines in response to LPS or ETEC, suggesting that PIE is a useful cell line for studying inflammatory responses via TLR4/MD-2 in intestinal epithelial cells.     

Toll-like receptor-4 (TLR4) mediates human β-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells

Monocytes are pivotal effector cells of the innate immune system that are vital for recognizing and eliminating invasive microbial pathogens. When microbial products bind to pathogen-recognition receptors, monocytes are activated and release a broad array of cytokines and defensins that orchestrate the host innate and adaptive immune responses. The aim of the present study is to investigate whether Toll-like receptor-4 (TLR4) mediates human β-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells. We showed that TLR4 is expressed in U937 cells and monocytes infected with viable microorganisms in a time-dependent fashion, while heat-inactivated microorganisms induced a lesser expression, albeit still significant, of TLR4 compared with viable organisms; flow cytometric analysis, in particular, revealed a higher level of TLR4 expression at 48 and 72 h postinfection. In addition, U937 cells and monocytes responded to C. pneumoniae in a TLR4-dependent manner with induction of mRNA and protein of the antimicrobial peptide HBD-2. The treatment of cells with TLR4-neutralizing antibody resulted in a decrease in C. pneumoniae- induced HBD-2 production. This study reveals that TLRs not only recognize ligands but also the types of effector molecules induced, namely, antimicrobial peptides. An understanding of the importance of the TLR-mediated antimicrobial mechanisms may provide new avenues for the development of therapeutic regimens aimed at activating the body's own defenses by stimulating TLR-dependent pathways.     

Cathelicidin antimicrobial peptides block dendritic cell TLR4 activation and allergic contact sensitization

Cathelicidins are antimicrobial peptides of the innate immune system that establish an antimicrobial barrier at epithelial interfaces and have been proposed to have a proinflammatory function. We studied the role of cathelicidin in allergic contact dermatitis, a model requiring dendritic cells of the innate immune response and T cells of the adaptive immune response. Deletion of the murine cathelicidin gene Cnlp enhanced an allergic contact response, whereas local administration of cathelicidin before sensitization inhibited the allergic response. Cathelicidins inhibited TLR4 but not TLR2 mediated induction of dendritic cell maturation and cytokine release, and this inhibition was associated with an alteration of cell membrane function and structure. Further analysis in vivo connected these observations because inhibition of sensitization by exogenous cathelicidin was dependent on the presence of functional TLR4. These observations provide evidence that cathelicidin antimicrobial peptides mediate an anti-inflammatory response in part by their activity at the membrane.     

Triggering of TLR3 by polyI:C in human corneal epithelial cells to induce inflammatory cytokines

Epithelial cells of the ocular surface are key in the first-line defense as a part of the mucosal immune system against pathogens. We investigated whether polyI:C induces the production by human corneal epithelial cells (HCEC) of pro-inflammatory cytokines and IFN-beta, and whether Toll-like receptor (TLR)-3 expression is amplified by polyI:C. TLR3 was expressed on the surface of HCEC. Stimulation with polyI:C elicited the elevated production and mRNA expression of IL-6 and IL-8 in HCEC. While polyI:C induced IFN-beta, far stronger than human fibroblasts, and TLR3 gene expression in HCEC, LPS stimulation did not. Similarly, polyI:C, but not LPS, induced the gene expression of IkappaBalpha and MAIL, members of the IkappaB family, in HCEC. The innate immune response of HCEC is distinct from that of immune-competent cells, and we suggest that this is indicative of the symbiotic relationship between corneal epithelium and microbes inhabiting the ocular surface.     

Human Toll-like receptor 4 responses to P. gingivalis are regulated by lipid A 1- and 4'-phosphatase activities

Signal transduction following binding of lipopolysaccharide (LPS) to Toll-like receptor 4 (TLR4) is an essential aspect of host innate immune responses to infection by Gram-negative pathogens. Here, we describe a novel molecular mechanism used by a prevalent human bacterial pathogen to evade and subvert the human innate immune system. We show that the oral pathogen, Porphyromonas gingivalis , uses endogenous lipid A 1- and 4'-phosphatase activities to modify its LPS, creating immunologically silent, non-phosphorylated lipid A. This unique lipid A provides a highly effective mechanism employed by this bacterium to evade TLR4 sensing and to resist killing by cationic antimicrobial peptides. In addition, lipid A 1-phosphatase activity is suppressed by haemin, an important nutrient in the oral cavity. Specifically, P. gingivalis grown in the presence of high haemin produces lipid A that acts as a potent TLR4 antagonist. These results suggest that haemin-dependent regulation of lipid A 1-dephosphorylation can shift P. gingivalis lipid A activity from TLR4 evasive to TLR4 suppressive, potentially altering critical interactions between this bacterium, the local microbial community and the host innate immune system.     

Development and characterization of synthetic glucopyranosyl lipid adjuvant system as a vaccine adjuvant

Innate immune responses to vaccine adjuvants based on lipopolysaccharide (LPS), a component of gram-negative bacterial cell walls, are driven by Toll-like receptor (TLR) 4 and adaptor proteins including MyD88 and TRIF, leading to the production of inflammatory cytokines, type I interferons, and chemokines. We report here on the characterization of a synthetic hexaacylated lipid A derivative, denoted as glucopyranosyl lipid adjuvant (GLA). We assessed the effects of GLA on murine and human dendritic cells (DC) by combining microarray, mRNA and protein multiplex assays and flow cytometry analyses. We demonstrate that GLA has multifunctional immunomodulatory activity similar to naturally-derived monophosphory lipid A (MPL) on murine DC, including the production of inflammatory cytokines, chemokines, DC maturation and antigen-presenting functions. In contrast, hexaacylated GLA was overall more potent on a molar basis than heterogeneous MPL when tested on human DC and peripheral blood mononuclear cells (PBMC). When administered in vivo, GLA enhanced the immunogenicity of co-administered recombinant antigens, producing strong cell-mediated immunity and a qualitative T(H)1 response. We conclude that the GLA adjuvant stimulates and directs innate and adaptive immune responses by inducing DC maturation and the concomitant release of pro-inflammatory cytokines and chemokines associated with immune cell trafficking, activities which have important implications for the development of future vaccine adjuvants.     

Allergic airway inflammation inhibits pulmonary antibacterial host defense

The innate immune system of the lung is a multicomponent host defense system and in addition has an instructing role in regulating the quality and quantity of the adaptive immune response. When the interaction between innate and adaptive immunity is disturbed, pathological conditions such as asthma can develop. It was the aim of the study to investigate the effect of the allergic inflammation of the lung on the innate host defense during bacterial infection. Human bronchial epithelial cells were preincubated with Th2 cytokines and infected with Pseudomonas aeruginosa. The effect of the Th2 cytokines on the mRNA levels of antimicrobial peptides and the antimicrobial activity of HBEC was determined. To investigate the influence of an allergic inflammation on pulmonary host defense in vivo, mice sensitized and challenged with OVA were infected with P. aeruginosa, and the number of viable bacteria in the lungs was determined together with markers of inflammation like cytokines and antimicrobial peptides. Exposure of airway epithelial cells to Th2 cytokines resulted in a significantly decreased antimicrobial activity of the cells and in suppressed mRNA levels of the antimicrobial peptide human beta-defensin 2. Furthermore, mice with allergic airway inflammation had significantly more viable bacteria in their lungs after infection. This was consistent with reduced levels of proinflammatory cytokines and of the antimicrobial peptide cathelin-related antimicrobial peptide. These results show that an allergic airway inflammation suppresses the innate antimicrobial host defense. The adaptive immune system modulates the functions of the pulmonary innate immune system.     

Immunophysiology of epithelial cells and pattern-recognition receptors

Many types of pattern-recognition receptors, including the group of signaling Toll-like receptors, have been found in epithelial cells. They serve for recognizing microorganisms, which induces the activation of epithelial cells followed by production of chemokines and antimicrobial substances. On the one hand, this attracts macrophages, neutrophils, and other cells of innate immunity eliminating microorganisms to the epithelial locus. The same pattern-recognition receptors are involved in cell activation resulting in the production of cytokines that trigger the controlled activation of adaptive-immunity cells. This leads to the formation of anti-bodies or cytotoxic T lymphocytes. On the other hand, activated epithelial cells produce an array of antimicrobial substances suppressing enteropathogenic microflora inhabiting external epithelial spaces. Conversely, local tolerance is developed with respect to predominant microflora of epithelial tracts. This tolerance encompasses both innate and adaptive immunities of subepithelial spaces. Although much remains to be understood regarding the mechanisms of its formation and maintenance, it is obvious that epithelial cells play an important role in these processes. Thus, epithelial cells “conduct” immune responses to both pathogenic microorganisms penetrating the host body and microorganisms inhabiting epithelial cellular spaces. The maintenance of the optimal composition of the microbial biocenosis of the human body is a function of its immune system.     

Innate responses of corneal epithelial cells against Aspergillus fumigatus challenge

Toll-like receptors (TLRs) are key components of the innate immune system that detects microbial infection and triggers host defensive responses. To determine the roles of TLR2 and TLR4 in corneal epithelial cells in mediating innate responses against Aspergillus fumigatus , telomerase-immortalized human corneal epithelial cells (THCE) were challenged by TLR2 ligand zymosan, TLR4 ligand lipopolysaccharide and A. fumigatus hyphae, respectively. Culture media were collected at different time points and enzyme-linked immunosorbent assay was performed to detect the levels of inflammatory cytokines interleukin-1β (IL-1β) and IL-6. We found that THCE responded to the challenge of TLR2 or TLR4 ligand by expressing and secreting inflammatory cytokines into the culture media. And exposure of THCE to A. fumigatus hyphae resulted in the upregulation of IL-1β and IL-6. Treatment with TLR2- or TLR4-siRNA plasmid reduced TLR2 or TLR4 expression level in THCE when compared with controls, and caused a significant decrease in A. fumigatus -induced IL-1β and IL-6 production. Our results suggested that THCE can respond to TLR2 and TLR4 ligand challenge by secreting IL-1β and IL-6. They recognize A. fumigatus hyphae via TLR2 and TLR4 and initiate innate immune responses. Corneal epithelial cells play a role in innate defense against fungal infection through the mediation of inflammatory cytokines production.     

Identification and Characterization of the First Cathelicidin from Sea Snakes with Potent Antimicrobial and Anti-inflammatory Activity and Special Mechanism

Cathelicidins are a family of gene-encoded peptide effectors of innate immunity found exclusively in vertebrates. They play pivotal roles in host immune defense against microbial invasions. Dozens of cathelicidins have been identified from several vertebrate species. However, no cathelicidin from marine reptiles has been characterized previously. Here we report the identification and characterization of a novel cathelicidin (Hc-CATH) from the sea snake Hydrophis cyanocinctus. Hc-CATH is composed of 30 amino acids, and the sequence is KFFKRLLKSVRRAVKKFRKKPRLIGLSTLL. Circular dichroism spectroscopy and structure modeling analysis indicated that Hc-CATH mainly assumes an amphipathic α-helical conformation in bacterial membrane-mimetic solutions. It possesses potent broad-spectrum and rapid antimicrobial activity. Meanwhile, it is highly stable and shows low cytotoxicity toward mammalian cells. The microbial killing activity of Hc-CATH is executed through the disruption of cell membrane and lysis of bacterial cells. In addition, Hc-CATH exhibited potent anti-inflammatory activity by inhibiting the LPS-induced production of nitric oxide (NO) and pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Hc-CATH directly binds with LPS to neutralize its toxicity, and it also binds to Toll-like receptor 4 (TLR4/MD2 complex), which therefore inhibits the binding of LPS to TLR4/MD2 complex and the subsequent activation of LPS-induced inflammatory response pathways. Taken together, our study demonstrates that Hc-CATH, the first cathelicidin from sea snake discovered to have both antimicrobial and anti-inflammatory activity, is a potent candidate for the development of peptide antibiotics.