Innate Immune Response Of Neutrophils Research Articles

Innate immune response in bovine neutrophils stimulated with Mycoplasma bovis

Mycoplasma bovis (M. bovis) is a significant worldwide pathogen of cattle. Neutrophils have an important role in the innate immune response during infection with M. bovis. However, even though neutrophils accumulate in M. bovis infection, the interaction of M. bovis and neutrophils has not been fully elucidated. We attempted to elucidate the innate immune response of neutrophils stimulated with M. bovis and evaluate the transcriptome and functional analysis of bovine neutrophils stimulated with M. bovis. Proinflammatory cytokines, such as inducible nitric oxide (iNOS), which was the most increased gene in transcriptome analysis, were increased in quantitative polymerase chain reaction analysis of bovine neutrophils stimulated with live or heat-killed M. bovis. Nitric oxide and intracellular reactive oxygen species production of neutrophils stimulated with M. bovis was significantly increased. Neutrophils stimulated with M. bovis showed an increased ratio of nonapoptotic cell death compared to unstimulated controls. We demonstrated that neutrophil extracellular traps (NETs) formation was not recognized in neutrophils stimulated with live M. bovis. However, heat-killed M. bovis induced NETs formation. We also showed the interaction with M. bovis and bovine neutrophils regarding proinflammatory cytokine gene expression and functional expression related to NETs formation. Live and killed M. bovis induced innate immune responses in neutrophils and had the potential to induce NETs formation, but live M. bovis escaped NETs.

Neutrophil Inflammatory Response Is Downregulated by Uptake of Superparamagnetic Iron Oxide Nanoparticle Therapeutics.

Superparamagnetic iron oxide nanoparticles (SPION) are employed as diagnostics and therapeutics following intravenous delivery for the treatment of iron deficiency anemia (IDA) in adult patients with chronic kidney failure. Neutrophils are the first defense against blood borne foreign insult and recruit to vascular sites of inflammation via a sequential process that is characterized by adhesive capture, rolling, and shear resistant arrest. A primary chemotactic agonist presented on the glycocalyx of inflamed endothelium is IL-8, which upon binding to its cognate membrane receptor (CXCR1/2) activates a suite of responses in neutrophils. An early response is degranulation with accompanying upregulation of β2-integrin (CD11/CD18) and shedding of L-selectin (CD62L) receptors, which exert differential effects on the efficiency of endothelial recruitment. Feraheme is an FDA approved SPION treatment for IDA, but its effect on the innate immune response of neutrophils during inflammation has not been reported. Here, we studied the immunomodulatory effects of Feraheme on neutrophils freshly isolated from healthy human subjects and stimulated in suspension or on inflammatory mimetic substrates with IL-8. Cells treated with Feraheme exhibited reduced sensitivity to stimulation with IL-8, indicated by reduced upregulation of membrane CD11b/CD18 receptors, high affinity (HA) CD18, and shedding of CD62L. Feraheme also inhibited N-formyl-Met-Leu-Phe (fMLP) induced reactive oxygen species production. Neutrophil rolling, arrest, and migration was assessed in vascular mimetic microfluidic channels coated with E-selectin and ICAM-1 to simulate inflamed endothelium. Neutrophils exposed to Feraheme rolled faster on E-selectin and arrested less frequently on ICAM-1, in a manner dependent upon SPION concentration. Subsequent neutrophil shape change, and migration were also significantly inhibited in the presence of Feraheme. Lastly, Feraheme accelerated clearance of cytosolic calcium flux following IL-8 stimulation. We conclude that uptake of Feraheme by neutrophils inhibits chemotactic activation and downregulates normal rolling to arrest under shear flow. The mechanism involves increased calcium clearance following chemotactic activation, which may diminish the efficiency of recruitment from the circulation at vascular sites of inflammation.

Toll-like receptor 4 plays an important role to enhance bacterial clearance from the nose in synergy with triggering receptor expressed on myeloid cells (TREM)-1 expression on polymorphonuclear neutrophils

ObjectiveAcute rhinosinusitis (ARS) is among the most common infectious diseases. Neutrophils play a major role in innate host defenses against pathogenic microorganisms such as fungi and bacteria. Recently, in neutrophils, ligation of the triggering receptor expressed on myeloid cells (TREM)-1 was found to activate the full spectrum of neutrophil effector mechanisms, including the release of inflammatory mediators, degranulation, phagocytosis, and oxidative burst in synergy with Toll-like receptors (TLRs). In this study, we investigated the effect of TREM-1 on the functions of neutrophils in relation to TLR4 in a nasal and nasopharyngeal inflammation mouse model via nontypeable Haemophilus influenzae (NTHi) intranasal inoculation. MethodsWe used C3H/HeJ (TLR4-deficient) mice, which arose spontaneously and have non-functional TLR4 protein, and normal wild-type (WT) C3H/HeN mice. Mice were inoculated intranasally with NTHi (107 cfu/mouse) to investigate the effects of TLR4 on the function of Neutrophils. We examined the kinetics of bacterial clearance and inflammatory cell infiltration in nasal washes at 6, 12, 24, and 72 h after inoculation. The expression of TREM-1 on neutrophils, and TREM-1 mRNA expression in neutrophils in the nasal washes were examined by flow cytometric analysis and RT-PCR. ResultsBacterial counts of NTHi from nasal washes were significantly lower in WT mice than in TLR4-mutant mice after inoculation. The numbers of inflammatory cells in nasal washes were significantly higher in WT mice at 6 h, 12 h, and 24 h after inoculation than in TLR4-deficient mice. The expression of TREM-1 protein on neutrophils and the mRNA levels were greater in WT mice than in TLR4-mutant mice. The concentrations of soluble TREM-1 in WT nasal washes were also significantly higher than in those of TLR4-deficient mice. ConclusionTREM-1 may play an important role together with TLR4 in the nasopharyngeal clearance of NTHi by neutrophils. Further studies will need to clarify the innate immune responses of neutrophils via TLR4 to prevent NTHi infection.

Mycoplasma bovis escapes bovine neutrophil extracellular traps

Mycoplasma bovis is a significant pathogen in bovine infections including mastitis, pneumonia, arthritis and otitis media, and is the cause of large economic losses in beef and dairy farms. During infection with M. bovis, recruited neutrophils are not sufficient to eradicate M. bovis from the infection site. The release of neutrophil extracellular traps (NETs) is one of the innate immune responses of neutrophils but the effect of M. bovis on NET formation by bovine neutrophils has not yet been clarified. The objective of our research was to examine the effect of M. bovis on NET formation and the killing activity of bovine neutrophils. We showed that NETs were not detected following stimulation of neutrophils by M. bovis alone or with Phorbol 12-myristate 13-acetat (PMA). Reactive oxygen species production is essential for NET formation but the levels in neutrophils stimulated with M. bovis at multiplicity of infections of 10, 100, and 1000 were similar to those of unstimulated cells. NET formation induced by PMA stimulated neutrophils disappeared following the addition of M. bovis but this phenomenon was not observed when ethylenediaminetetraacetic acid (EDTA) was added. M. bovis colony forming units were significantly decreased by the addition of EDTA in the presence of NETs. Our results suggested that M. bovis infection alone did not induce NETs and that M. bovis nucleases, as hypothesis-based, contributed to resistance against the killing activity of NETs.

143: Nod2 and Rip2 contribute to innate immune responses in mouse neutrophils

Nod-like receptors (NLRs) are a family of innate immune receptors that link cytosolic sensing of microbial and danger stimuli to the activation of immune responses. Two NLR family members, Nod1 and Nod2, recognize bacterial peptidoglycan and activate immune responses via NF-κB and MAPK. The function of Nod1 and Nod2 has been largely studied in macrophages, but the role of these receptors in other innate immune cells remains unclear. In this study, we examined the function of Nod1 and Nod2 in innate immune responses of neutrophils. Mice were injected i.p with thioglycollate, and then peritoneal neutrophils were isolated 4 h after injection. Tri-DAP and muramyl-dipeptide (MDP) were used as Nod1 and Nod2 agonist, respectively. The level of cytokines (IL-6 and TNF-α) and chemokines (CXCL1 and CCL2) was increased by MDP, but not Tri-DAP in WT neutrophils. Such production of cytokines and chemokines by MDP was abolished in Nod2- and Rip2-deficient neutrophils. MDP also induced the activation of NF-κB and MAPK in WT neutrophils, but not Nod2- and Rip2-deficient cells. Flow cytometry analysis showed that L-selectin shedding was induced by MDP in WT neutrophils, but not in Nod2- and Rip2-deficient cells. MDP and TLR agonists (Pam3CSK4 and LPS) exerted synergistic effect on the production of IL-6 and CXCL1 in neutrophils. Moreover, Nod2 and TLR4 cooperated to produce IL-6, TNF-α, CXCL1, and CCL2 in neutrophils in response to gram-negative bacteria. Our findings suggest that Nod2-Rip2 axis may contribute to innate immune response of neutrophils against bacterial infection.

Nod2 and Rip2 contribute to innate immune responses in mouse neutrophils.

Nod-like receptors are a family of innate immune receptors that link cytosolic sensing of microbial and danger stimuli to the activation of immune responses. Two Nod-like receptor family members, Nod1 and Nod2, recognize bacterial peptidoglycan and activate immune responses via nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK). The function of Nod1 and Nod2 has been largely studied in macrophages, but the role of these receptors in other innate immune cells remains unclear. In this study, we examined the function of Nod1 and Nod2 in innate immune responses of neutrophils. Mice were injected intraperitoneally with thioglycollate, and then peritoneal neutrophils were isolated 4 hr after injection. Tri-DAP and muramyl-dipeptide (MDP) were used as Nod1 and Nod2 agonists, respectively. The level of cytokines [interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α)] and chemokines (CXCL1 and CCL2) was increased by MDP, but not Tri-DAP in wild-type (WT) neutrophils. Increased production of cytokines and chemokines with MDP was abolished in Nod2- and Rip2-deficient neutrophils. MDP also induced the activation of NF-κB and MAPK in WT neutrophils, but not in Nod2- and Rip2-deficient cells. Flow cytometry analysis showed that L-selectin shedding was induced by MDP in WT neutrophils, but not in Nod2- and Rip2-deficient cells. MDP and Toll-like receptor (TLR) agonists (Pam3 CSK4 and lipopolysaccharide) exerted synergistic effects on the production of IL-6 and CXCL1 in neutrophils. Moreover, Nod2 and TLR4 cooperated to produce IL-6, TNF-α, CXCL1 and CCL2 in neutrophils in response to Gram-negative bacteria. Our findings suggest that the Nod2-Rip2 axis may contribute to the innate immune response of neutrophils against bacterial infection.

Migrational Guidance of Neutrophils Is Mechanotransduced via High-Affinity LFA-1 and Calcium Flux

Acute inflammation triggers the innate immune response of neutrophils that efficiently traffic from the bloodstream to concentrate at high numbers at the site of tissue infection or wounding. A gatekeeper in this process is activation of β(2) integrins, which form bond clusters with ICAM-1 on the endothelial surface. These bond clusters serve dual functions of providing adhesive strength to anchor neutrophils under the shear forces of blood flow and directional guidance for cell polarization and subsequent transmigration on inflamed endothelium. We hypothesized that shear forces transmitted through high-affinity LFA-1 facilitates the cooperation with the calcium release-activated channel Orai1 in directing localized cytoskeletal activation and directed migration. By using vascular mimetic microfluidic channels, we observed neutrophil arrest on a substrate of either ICAM-1 or allosteric Abs that stabilize a high- or low-affinity conformation of LFA-1. Neutrophils captured via low-affinity LFA-1 did not exhibit intracellular calcium flux, F-actin polymerization, cell polarization, or directional migration under shear flow. In contrast, high-affinity LFA-1 provided orientation along a uropod-pseudopod axis that required calcium flux through Orai1. We demonstrate how the shear stress of blood flow can transduce distinct outside-in signals at focal sites of high-affinity LFA-1 that provide contact-mediated guidance for neutrophil emigration.

Shear forces and high affinity LFA-1 drive PMN recruitment (102.18)

Abstract Acute inflammation triggers the innate immune response of neutrophils that efficiently traffic from the blood stream to concentrate at high numbers at the site of tissue infection or wounding. A gatekeeper in this process is activation of β2-integrins, which forms bond clusters with ICAM-1 on the endothelial surface. These bond clusters serve dual functions of providing adhesive strength to anchor neutrophils under the shear forces of blood flow and directional guidance for cell polarization and subsequent transmigration on inflamed endothelium. We hypothesized that shear forces transmitted through high affinity LFA-1 facilitates their cooperation with the calcium release activated channel (CRAC) Orai1 in directing localized cytoskeletal activation and directed migration. Employing vascular mimetic microfluidic channels we observed neutrophils arresting on a substrate of either ICAM-1 or allosteric antibodies that stabilize a high or low affinity conformation of LFA-1. Neutrophils captured via low affinity LFA-1 did not exhibit intracellular calcium flux, F-actin polymerization, cell polarization, or directional migration under shear flow. In contrast, high affinity LFA-1 provided orientation along a uropod-pseudopod axis that required calcium flux through Orai1. We demonstrate how the shear stress of blood flow can transduce distinct outside-in signals at focal sites of high affinity LFA-1 that provides contact mediated guidance for neutrophil emigration.

Deficiency In Stress Response Gadd45a and Gadd45b Alters MAPK Kinase Signaling Leading to Functional Defects In Innate Immune Responses of Neutrophils and Macrophages In Vitro and In Vivo

AbstractAbstract 927Stress sensor GADD45 proteins modulate p38-NF-Kb and JNK signaling; which play major roles in leukocyte activation and innate immunity. We have previously documented that GADD45a-deficient and GADD45b-deficient mice exhibit impaired responses to hematological stress, including acute stimulation with inflammatory cytokines (Gupta et. al, Oncogene. 25:5537, 2006). Whether GADD45 genes modulate myeloid compartment function, notably the response of macrophages & granulocytes to inflammatory stress, remains largely unexplored. Data obtained thus far indicate that bone marrow (BM) derived neutrophils and macrophages lacking GADD45 family members exhibit defects in chemotaxis towards inflammatory stimuli. BM derived neutrophils and macrophages lacking GADD45 family members were also observed to exhibit defects in the production of reactive oxygen species (ROS) upon treatment with LPS (500ng/mL) in vitro. Furthermore, BM derived macrophages from mice lacking GADD45a and GADD45b were found to be defective in phagocytosis and cellular adhesion upon stimulation with LPS (500ng/mL) in vitro. Additionally, it was observed that BM derived neutrophils and macrophages lacking GADD45 family members exhibit defects in inflammatory cytokine secretion in response to activation with LPS. Notably, GADD45a, GADD45b & GADD45g null mice injected intraperitoneally with sublethal doses of LPS were significantly more susceptible to septic shock compared to wt mice, showing significantly increased morbidity. Moreover at 18 hrs. post-injection, the spleens of KO mice harbored apoptotic foci in the white pulp, identified as tingible body macrophages ingesting dying cells. To dissect the signaling pathways involved, MAPK specific chemical inhibitors were used to correlate MAPK signaling alteration to defects in innate immune responses of neutrophils and macrophages lacking GADD45a or GADD45b. LPS stimulated wt neutrophils treated with MAPK inhibitors exhibited defects in signaling and innate immune responses mimicking neutrophils and macrophages lacking GADD45a or GADD45b. Collectively, these novel data provide evidence to show that deficiency in GADD45a and GADD45b leads to functional defects in the myeloid innate immune responses of neutrophils and macrophages in vitro and in vivo. These findings increase our understanding of innate immunity and have the potential to contribute towards development of novel approaches to clinical treatment of sepsis. Disclosures:No relevant conflicts of interest to declare.