Monocyte chemoattractant protein 1 regulates pulmonary host defense via neutrophil recruitment during Escherichia coli infection

Neutrophil accumulation is a critical event to clear bacteria. Since uncontrolled neutrophil recruitment can cause severe lung damage, understanding neutrophil trafficking mechanisms is important to attenuate neutrophil-mediated damage. While monocyte chemoattractant protein 1 (MCP-1) is known to be a monocyte chemoattractant, its role in pulmonary neutrophil-mediated host defense against Gram-negative bacterial infection is not understood. We hypothesized that MCP-1/chemokine (C-C motif) ligand 2 is important for neutrophil-mediated host defense. Reduced bacterial clearance in the lungs was observed in MCP-1(-/-) mice following Escherichia coli infection. Neutrophil influx, along with cytokines/chemokines, leukotriene B(4) (LTB(4)), and vascular cell adhesion molecule 1 levels in the lungs, was reduced in MCP-1(-/-) mice after infection. E. coli-induced activation of NF-κB and mitogen-activated protein kinases in the lung was also reduced in MCP-1(-/-) mice. Administration of intratracheal recombinant MCP-1 (rMCP-1) to MCP-1(-/-) mice induced pulmonary neutrophil influx and cytokine/chemokine responses in the presence or absence of E. coli infection. Our in vitro migration experiment demonstrates MCP-1-mediated neutrophil chemotaxis. Notably, chemokine receptor 2 is expressed on lung and blood neutrophils, which are increased upon E. coli infection. Furthermore, our findings show that neutrophil depletion impairs E. coli clearance and that exogenous rMCP-1 after infection improves bacterial clearance in the lungs. Overall, these new findings demonstrate that E. coli-induced MCP-1 causes neutrophil recruitment directly via chemotaxis as well as indirectly via modulation of keratinocyte cell-derived chemokine, macrophage inflammatory protein 2, and LTB(4).     

Role of Janus kinase 3 in mast cell-mediated innate immunity against gram-negative bacteria

Mast cells play a pivotal role in innate host immune response to gram-negative bacteria. We report that Janus kinase 3 plays a role in mast cell-mediated bacterial clearance and neutrophil recruitment by regulating the release of tumor necrosis factor from mast cells. The role of JAK3 in mast cell-facilitated neutrophil recruitment and bacterial clearance was investigated by comparing the neutrophil influxes and bacterial clearance in mast cell-deficient W/W(v) mice reconstituted with JAK3(+/+) or JAK(-/-) mast cells. The neutrophil influx, bacterial clearance, and survival outcome in W/W(v) mice reconstituted with JAK3(+/+) mast cells was better than in W/W(v) mice reconstituted with JAK3(-/-) mast cells. These findings provide evidence that JAK3 is a key regulator of mast cell-mediated innate immunity against gram-negative bacteria.     

Myeloid differentiation protein-2-dependent and -independent neutrophil accumulation during Escherichia coli pneumonia

Bacterial pneumonia remains a serious disease. Pattern recognition receptors play an integral role in neutrophil accumulation during pneumonia. Although myeloid differentiation protein (MD)-2 has been recognized as a key molecule for LPS signaling, the role of MD-2 in neutrophil accumulation in the lung during bacterial infection has not been explored. Here, we investigate the role of MD-2 in Escherichia coli LPS-induced lung inflammation and E. coli-induced pneumonia. LPS-induced CD14-independent neutrophil accumulation was abolished in CD14/MD-2(-/-) mice. MD-2(-/-) mice challenged with LPS displayed attenuated neutrophil influx, NF-kappaB activation, cytokine/chemokine expression, and lung histopathology. MD-2(-/-) mice transplanted with MD-2(+/+) bone marrow demonstrated decreased neutrophil influx and cytokine/chemokine expression in the lungs when challenged by LPS. MD-2(-/-) mice infected with E. coli demonstrated reduced neutrophil influx and cytokine/chemokine expression in the lungs, whereas heat-killed E. coli did not induce either neutrophil accumulation or cytokine/chemokine expression in MD-2(-/-) mice infected with E. coli. Furthermore, MD-2(-/-) mice displayed increased bacterial burden in the lungs and enhanced bacterial dissemination. Toll-like receptor (TLR)-5(-/-) mice infected with E. coli exhibited attenuated neutrophil accumulation, whereas MD-2/TLR5(-/-) mice inoculated with E. coli showed further attenuated neutrophil influx and impaired bacterial clearance. Taken together, these new findings demonstrate: (1) the important role of MD-2 in the CD14-independent LPS-mediated cascade of neutrophil influx; (2) the relative importance of bone marrow- and non-bone marrow cell-derived MD-2 in LPS-induced inflammation; and (3) the essential role of MD-2-dependent and MD-2-independent (TLR5) signaling in E. coli-induced neutrophil accumulation and pulmonary host defense.     

Role of mast cells in zymosan-induced peritoneal inflammation in Balb/c and mast cell-deficient WBB6F1 mice

Zymosan-induced peritonitis was investigated in mast cell-deficient WBB6F1 mice and in Balb/c mice pretreated with mast cell stabilizer (cromolyn) or antagonists of histamine receptors (mepyramine, triprolidine, cimetidine, or ranitidine). The inherited mast cell deficiency in W/Wv knockouts of WBB6F1 mice impaired significantly the level of histamine and plasma exudation (measured 30 min after stimulation) as well as the influx of exudatory leukocytes, accumulation of plasma and exudate chemoattractants, and the release of proinflammatory cytokines (TNF-alpha, IL-1beta, and IL-6) measured at 6 h of inflammation. All of those factors were fully restored after selective intraperitoneal reconstitution of W/Wv mice with bone marrow-derived mast cells from their control +/+ counterparts. Cromolyn pretreatment of Balb/c mice reduced exclusively the early plasma exudation and histamine influx. Blocking of histamine receptors inhibited not only the early plasma exudation but also temporarily diminished primary leukocyte influx and levels of MCP-1 and IL-1beta. In conclusion, mast cells play an important role in the initiation of zymosan-induced peritonitis and modulate its further course.     

Adoptive transfer of mast cells does not enhance the impaired survival of Kit(W)/Kit(W-v) mice in a model of low dose intraperitoneal infection with bioluminescent Salmonella typhimurium

Mast cells are important effector cells in IgE-associated immune responses, but also can contribute to host defense in certain examples of bacterial infection. We found that genetically mast cell-deficient WBB6F1-Kit(W)/Kit(W-v) mice exhibited more bacterial CFUs per spleen by 6 days after intraperitoneal injection of bioluminescent Salmonella typhimurium, and died more rapidly after infection, than did the congenic WBB6F1-Kit(+/+) wild type mice. Adoptive transfer of bone marrow-derived cultured mast cells of Kit(+/+) origin to the peritoneal cavity of Kit(W)/Kit(W-v) mice resulted in engraftment of mast cells in the peritoneal cavity and mesentery of the recipient mice, and the development of large numbers of mast cells in the spleen. However, such mast cell-engrafted Kit(W)/Kit(W-v) mice appeared sicker after intraperitoneal injection with S. typhimurium than did mast cell-deficient Kit(W)/Kit(W-v) mice, and exhibited numbers of CFUs of bacteria per spleen, and a survival curve, that were not significantly different than those of Kit(W)/Kit(W-v) mice. These results, when taken together with prior studies investigating the roles of mast cells in innate immunity, strongly suggest that whether mast cells can be shown to have a significant role in enhancing survival during bacterial infections may depend critically on the details of the particular experimental systems examined.     

Mast cells contribute to fibrin deposition in reverse passive Arthus reaction in mouse skin.

The activation of the clotting system is an important process during inflammation to contain the injury and initiate tissue repair. In the present study, we investigated the effect of mast cells on fibrin deposition in reverse passive Arthus reaction in mast cell-deficient WBB6F1-W/Wv(W/Wv) and control WBB6F1-(+)/+(+/+) mice, that were given 125I-labeled fibrogen intravenousty. An antibody dose-dependent increase in radioactivity was observed in the challenged skin sites. Sequential water and urea extractions characterized the radioiodinated fibrinogen derivatives present in the tissue. The radioactivity found in the various fractions of the stimulated samples from +/+ was 2-10-fold higher than that in specimens from W/Wv mice. The greatest difference was observed in the urea-insoluble pellet (cross-linked fibrin and its early degradation products). Reconstitution of W/Wv mice with mast cells augmented the response to levels similar to those in +/+ mice. Pretreatment with the antihistamine pyrilamine blocked the accumulation of 125I-labeled fibrinogen and its derivatives by approximately 70% in +/+ but not in W/Wv mice. Inhibition of leukotriene synthesis by A-63162 markedly decreased the accumulation of iodinated fibrinogen in both +/+ and W/Wv mice. The data suggest that mast cells and their vasoactive mediator histamine contribute to the exudation of clotting factors, which results in fibrin deposition and that mast cells also enhance fibrin cross-linkage.     

Differential involvement of toll-like receptors 2 and 4 in the host response to acute respiratory infections with wild-type and mutant Haemophilus influenzae strains

We used a mouse model of acute respiratory infections to investigate the role of Toll-like receptor 2 (TLR2) and TLR4 in the host response to Haemophilus influenzae. Acute aerosol exposures to wild-type strains of H. influenzae showed that TLR4 function was essential for TNF-alpha induction, neutrophil influx, and bacterial clearance. To determine how lipooligosaccharide (LOS) modifications would affect the role of TLR4 in inducing the host response, we used acute infections with an H. influenzae strain expressing a mutation in the htrB gene. This mutant strain expresses an LOS subunit with decreased acylation. In response to H. influenzae htrB infection, tumor necrosis factor alpha (TNF-alpha) secretion remained TLR4 dependent. But the decrease in LOS acylation made the neutrophil influx and the bacterial clearance also dependent on TLR2, as shown by the decreased host response elicited in TLR2 knockout mice compared to C57BL/6 mice. A subsequent analysis of TLR2 and TLR4 gene expression by quantitative PCR indicated that TLR4 function induces TLR2 expression and vice versa. These results indicate that some changes in the LOS subunit of H. influenzae can favor signaling through non-TLR4 receptors, such as TLR2. The results also indicate a close interaction between TLR4 and TLR2 that tightly regulates the expression of both receptors.     

Mast cells limit systemic bacterial dissemination but not colitis in response to Citrobacter rodentium

Enteropathogenic Escherichia coli and enterohemorrhagic E. coli cause an inflammatory colitis in human patients characterized by neutrophil infiltration, proinflammatory cytokine expression, and crypt hyperplasia. Citrobacter rodentium causes a similar colitis in mice and serves as a model for enteropathogenic E. coli infection in humans. C. rodentium induces systemic T-cell-dependent antibody production that facilitates clearance of the bacteria and protects the host from reinfection. The role of innate immune cells in infectious colitis, however, is less well understood. In this study, we have determined the role of mast cells in the inflammatory response and disease induced by C. rodentium. Mice deficient in mast cells exhibit more severe colonic histopathology and have a higher mortality rate following infection with C. rodentium than do wild-type animals. Despite unimpaired neutrophil recruitment and lymphocyte activation, mast cell-deficient mice have a disseminated infection evident in crucial organ systems that contributes to sepsis. Importantly, mast cells also have the capacity to directly kill C. rodentium. Together, these results suggest that mast cells protect the host from systemic infection by reducing the bacterial load and preventing dissemination of the bacterium from the colon.     

Neutrophil recruitment in immunized mice depends on MIP-2 inducing the sequential release of MIP-1alpha, TNF-alpha and LTB(4)

Neutrophils are thought to play an important role in the tissue damage observed in various autoimmune diseases. Chemokines, cytokines and leukotrienes have recognized roles in the orchestration of neutrophil migration. We have recently shown that antigen-induced neutrophil migration into the peritoneum of immunized mice is mediated by macrophage-inflammatory protein (MIP)-1alpha which interacts with CCR1 and induces the sequential release of TNF-alpha and leukotriene B(4) (LTB(4)). The present study investigates the role of MIP-2 and CXCR2 in the cascade of events leading to mediator generation and neutrophil influx. Antigen challenge of immunized mice induced the expression of CXCR2 and the production of KC and MIP-2 proteins. Antigen-induced neutrophil migration was inhibited by a CXCR2 receptor antagonist (repertaxin) or an anti-MIP-2 antibody, but not by an anti-KC antibody. Administration of MIP-2 promoted a dose-dependent neutrophil migration in naive mice which was inhibited by repertaxin, anti-TNF-alpha, anti-MIP-1alpha antibodies or by MK886 (leukotriene synthesis inhibitor). MIP-2 administration induced the release of MIP-1alpha, TNF-alpha and LTB(4), and the release of the latter two was inhibited by anti-MIP-1alpha antibody treatment. Our studies highlight the intricate balance between mediator production and action during an immune-mediated inflammatory response and suggest a mediator cascade leading to neutrophil influx following antigen challenge of immunized mice: MIP-2 --> MIP-1alpha --> TNF-alpha --> LTB(4).     

Expression of mast-cell-specific proteases in tissues of mice studied by in situ hybridization.

The protease mRNA expression phenotype of individual mast cells was studied by in situ hybridization. Mouse mast cell protease (MMCP)-2 mRNA was expressed by mast cells located in the mucosa of the stomach of WB(-)+/+ and (WB x C57BL/6)F1(-)+/+ (hereafter WBB6F1(-)+/+) mice but not by mast cells in the same tissue of C57BL/ 6(-)+/+ mice. Even in the stomach of WBB6F1(-)+/+ mice, mast cells located in the muscularis propria did not express MMCP-2 mRNA. The mRNAs of MMCP-4 and mouse mast cell carboxypeptidase A were not expressed by mast cells in the stomach mucosa of untreated WBB6F1(-)+/+ mice but were expressed after the infection of Strongyloides venezuelensis. We examined whether MMCP-2 mRNA expression varied by changing environments of mast cells. Cultured mast cells of WBB6F1(-)+/+ mice that expressed MMCP-2 mRNA were transplanted into the stomach wall of genetically mast-cell-deficient WBB6F1(-)W/Wv mice. Mast cells that appeared in the mucosa expressed the MMCP-2 mRNA, but mast cells that appeared in the muscularis propria did not, indicating the adaptation of cultured mast cells into a new environment. In contrast to cultured mast cells, peritoneal mast cells of WBB6F1(-)+/+ mice that expressed MMCP-2 mRNA as well did not adapt to the muscularis propria of WBB6F(1)-W/Wv mice. The MMCP-2 mRNA remained to be expressed after the settlement in either the mucosa or the muscularis propria. Furthermore, the peritoneal mast cells did not change the MMCP-4 and MMCP-6 mRNA expression phenotype after the settlement in either the mucosa or the muscularis propria of WBB6F(1)-W/Wv mice. The present result indicated that both intracellular factors such as strain specificity and source of mast cells and extracellular factors such as tissue specificity and helminth infection influenced the protease expression phenotypes.     

Bleomycin-induced pulmonary fibrosis in genetically mast cell-deficient WBB6F1-W/Wv mice and mechanism of the suppressive effect of tranilast, an antiallergic drug inhibiting mediator release from mast cells, on fibrosis.

It has been well known that the number of mast cells increases during the development of fibrosis in various tissues including the lung. However, the role of mast cells in fibrosis still remains obscure. In the present paper, we evidenced that pulmonary fibrosis could be induced in genetically mast cell-deficient WBB6F1-W/Wv mice as well as WBB6F1-(+/+) mice having mast cells normally by the treatment with bleomycin (BLM, 5 mg/kg, i.v., 10 days), and there was not much difference in the histological changes of lungs between the two strains. An increase in the hydroxyproline content of the lung of WBB6F1-W/Wv mice was rather higher than that of WBB6F1-(+/+) mice. Previously, we reported that tranilast, an antiallergic drug inhibiting chemical mediator release from mast cells, suppressed the development of BLM-induced pulmonary fibrosis in ICR mice, suggesting the possibility that mast cells play certain roles in fibrosis. However, it was evidenced in the present report that tranilast suppressed BLM-induced fibrosis in WBB6F1-W/Wv mice. Tranilast neither suppressed the cytotoxic activity of BLM against KB cells and L-929 cells in vitro, nor inhibited the antitumor activity of BLM against Sarcoma-180 transplanted subcutaneously into ICR mice. Tranilast may act through suppressing BLM-induced activation of lymphoid cells including macrophage and neutrophil. These results indicate an inconsequential role of mast cells in the development of fibrosis. Increases in the number of mast cells and in histamine content of the lung, which were widely reported in the lungs of BLM-treated mice, may be the result of fibrosis.     

Mast cells protect against airway Mycoplasma pneumoniae under allergic conditions

Background Infection with Mycoplasma pneumoniae (Mp) in asthma can occur both acutely and chronically with an associated Th2 inflammatory response and/or increased numbers of bronchial mast cells. Mast cells have previously been shown to promote mycoplasma clearance in mice; however, it is unknown whether mast cells would aid Mp clearance under allergic conditions. Objective Our aim was to determine the impact of allergic inflammation on mast cell‐mediated lung Mp clearance. Furthermore, as we have previously demonstrated an essential role for IL‐6 in lung Mp clearance we also investigated the role of mast cell‐derived IL‐6. Methods Mast cell‐deficient (WBB6F1/J‐Kit^W/Kit^W‐v) mice were challenged with ovalbumin to induce airway inflammation before Mp infection. The role of mast cell‐derived IL‐6 in bacterial clearance was further investigated by reconstitution of mast cell‐deficient mice with IL‐6^?/? mast cells. Results Allergic mast cell‐deficient mice exhibited increased lung Mp burden compared with control littermates. Intravenous adoptive transfer of wild‐type and IL‐6^?/? mast cells significantly improved Mp clearance in mast cell‐deficient mice. Acutely after Mp infection, allergen‐challenged mast cell‐deficient mice had increased levels of the pro‐inflammatory cytokines IL‐6 and TNF‐α in the bronchoalveolar lavage (BAL) fluid. The total number of neutrophils was also increased in mast cell‐deficient mice. Conclusions Our results establish that mast cells aid host defense against Mp in an allergic setting and that while IL‐6 is necessary for lung Mp clearance, mast cell‐derived IL‐6 is not required. Cite this as: N. M. Michels, H. W. Chu, S. C. LaFasto, S. R. Case, M. N. Minor and R. J. Martin, Clinical & Experimental Allergy, 2010 (40) 1406–1413.     

CXC chemokine receptor CXCR2 is essential for protective innate host response in murine Pseudomonas aeruginosa pneumonia

Pulmonary infection due to Pseudomonas aeruginosa has emerged as a leading cause of mortality. A vigorous host response is required to effectively clear the organisms from the lungs. This host defense is dependent on the recruitment and activation of neutrophils and macrophages. A family of chemotactic cytokines (chemokines) has been shown to participate in this protective response. In this study, we assessed the role of the ELR(+) (glutamic acid-leucine-arginine motif positive) CXC chemokines and their CXC chemokine receptor (CXCR2) in lung antibacterial host defense. The intratracheal administration of Pseudomonas to mice resulted in the time-dependent influx of neutrophils to the lung, peaking at 12 to 24 h after inoculation. The influx of neutrophils was associated with a similar time-dependent expression of the ELR(+) CXC chemokines, KC, macrophage inflammatory protein 2 (MIP-2), and lipopolysaccharide-induced CXC chemokine (LIX). Selective neutralization of MIP-2 or KC resulted in modest changes in neutrophil influx but no change in bacterial clearance or survival. However, neutralization of CXCR2 resulted in a striking increase in mortality, which was associated with a marked decrease in neutrophil recruitment and bacterial clearance. Conversely, the site-specific transgenic expression of KC resulted in enhanced clearance of bacteria after Pseudomonas challenge. This study indicates that ELR(+) CXC chemokines are critical mediators of neutrophil-mediated host defense in Pseudomonas pneumonia.     

Lipoteichoic acids selectively stimulate rat mast cells to cysteinyl leukotriene generation and affect mast cell migration after tumor necrosis factor (TNF)-priming

It is well established that mast cells play a critical role in the host defense against bacteria. Upon stimulation with bacteria and their antigens, mast cells release various mediators and cytokines that promote the development of inflammation at the site of infection. In the present study, we examined the ability of lipoteichoic acids (LTAs), some of the major components of cell walls of most gram-positive bacteria, to stimulate mast cell degranulation and histamine release as well as to generate of cysteinyl leukotrienes (LTs). We also studied the influence of LTAs on mast cell migration. Experiments were done on rat peritoneal mast cells and LTA from Staphyloccocus aureus and LTA from Bacillus subtilis were used. We have stated that neither S. aureus LTA nor B. subtilis LTA used at a wide range of concentrations (from 10(-4) to 10(5)ng/mL) induced mast cell degranulation and histamine release. However, stimulation of mast cells with both LTAs resulted in generation and release of significant levels of LTs. We have also documented that none of the LTAs stimulated rat mast cell migration, even in the presence of laminin. IL-6 priming did not influence mast cell migration towards LTAs, whereas, pretreatment of mast cells with TNF caused time-dependent mast cell migration in response to LTAs stimulation. Pretreatment of mast cells with anti-TNFR1 antibodies completely inhibited LTA-induced migratory response of TNF-primed mast cells. Our results showed that LTAs might be among important bacterial antigens involved in mast cell activation during bacterial infections.     

4-1BB (CD137) is required for rapid clearance of Listeria monocytogenes infection

4-1BB (CD137), a member of the tumor necrosis factor receptor superfamily, is a T-cell-costimulatory receptor that is expressed on activated T cells, dendritic cells, and NK cells. Little has been reported about its role in early host defense against bacterial infection. In this study, we report that 4-1BB-deficient (4-1BB(-/-)) mice are much more susceptible to Listeria monocytogenes (intracellular bacteria) infections than wild-type mice. Upon L. monocytogenes infection, 4-1BB(-/-) mice showed a lower survival rate, a higher bacterial burden in organs, and larger hepatic microabscesses than 4-1BB(+/+) mice. 4-1BB(-/-) mice also had impairment in clearance of bacteria from the bloodstream. Neutrophils from 4-1BB(+/+) mice constitutively expressed 4-1BB, which could be activated to induce intracellular Ca(2+) influx by ligation with anti-4-1BB antibody. On the other hand, neutrophils from 4-1BB(-/-) mice were defective in reactive oxygen species generation, phagocytic activities, and intracellular Ca(2+) mobilization. In addition, mice pretreated with anti-4-1BB monoclonal antibody were much more resistant to L. monocytogenes infection than control antibody-treated mice. Our results support the notion that 4-1BB may play a major role in host defense against intracellular pathogens through neutrophil activation.     

Roles of tumor necrosis factor receptor signaling during murine Escherichia coli pneumonia

We hypothesized that tumor necrosis factor (TNF)-alpha signaling is essential to inflammation and host defense during Escherichia coli pneumonia. We tested this hypothesis by instilling E. coli into the lungs of wild-type (WT) mice and gene-targeted mice that lack both p55 and p75 receptors for TNF-alpha. The emigration of neutrophils 6 h after instillation of E. coli was not decreased, but rather was significantly increased (167% of WT), in TNF receptor (TNFR)-deficient mice. This increased neutrophil emigration did not result from peripheral blood neutrophilia or enhanced neutrophil sequestration, inasmuch as the numbers of neutrophils in the circulating blood and in the pulmonary capillaries did not differ between TNFR-deficient and WT mice. The accumulation of pulmonary edema fluid was not inhibited in TNFR-deficient compared with WT mice. Nuclear factor-kappaB (NF-kappaB) translocation in the lungs was not prevented in TNFR-deficient mice. Thus, signaling pathways independent of TNFRs can mediate the acute inflammatory response during E. coli pneumonia. However, despite this inflammatory response, bacterial clearance was impaired in TNFR-deficient mice (109 +/- 8% versus 51 +/- 14% of the original inoculum viable after 6 h in TNFR-deficient and WT mice, respectively). Increased neutrophil emigration during E. coli pneumonia in TNFR-deficient mice may thus result from an increased bacterial burden in the lungs. During acute E. coli pneumonia, the absence of TNFR signaling compromised bacterial killing, but did not prevent inflammation, as measured by the accumulation of edema fluid and neutrophils.     

Immune protection against septic peritonitis in endotoxin-primed mice is related to reduced neutrophil apoptosis

The innate immune system provides essential information about the presence of infectious danger and signals the activation and instruction of adaptive immunity. The present study addressed the question of whether prior exposure of the innate immune system to LPS may modulate host defense against acute septic peritonitis. We show that LPS priming 4 days, but not 2 days, prior to infection enhances bacterial clearance and improves survival of septic peritonitis. Immune protection in day 4 LPS-primed mice was specifically associated with a marked increase in the accumulation and activation of neutrophils at the site of infection. Accumulating neutrophils in day 4 LPS-primed mice exhibited a normal production of reactive oxygen metabolites in response to in vivo exposure to intestinal bacteria. The local increase in neutrophil numbers was found to result from a reduced rate of apoptotic cell death. Inhibition of neutrophil apoptosis in LPS-primed mice was mediated by soluble factor(s) distinct from G-CSF and GM-CSF. Thus, engagement of pattern recognition systems prior to infection may improve host defense by amplifying the effector cell response of innate immunity. The results also provide in vivo evidence that apoptosis of inflammatory cells represents an important process for the control of host defense to infection.     

Inflammatory processes in a murine model of intra-abdominal abscess formation.

Abscess formation has been viewed as a host defense strategy to contain the spread of infection. However, abscesses are also serious and life-threatening manifestations of persisting microbial infection. The initiation of abscess formation, both clinically and experimentally, involves the release of bacteria and an abscess-potentiating agent (e.g., fecal fiber or an analog) into a sterile site, with host defense mechanisms being unable to eliminate the infecting organisms. Abscess formation is aided by a combination of factors that share a common feature: impairment of phagocytic killing and hence clearance of microorganisms. These include bacterial virulence factors (e.g., capsule formation, succinic acid production); complement activation by the abscess potentiating agent; fibrin deposition; and microbial sequestration within abscess neutrophils. Recruitment of cells into the peritoneal cavity follows mast cell activation in the pathogenesis of infection: histamine and tumor necrosis factor alpha can be detected in the peritoneal cavity within minutes of challenge with an abscess-inducing mixture. However, the role of mast cells in host defense is made less clear by the finding of diminished abscess formation (but no mortality or increased morbidity) in mast-cell-depleted mice. This may indicate that mast cell products have a role in not only the initiation of an inflammatory response but also the promotion of fibrin deposition and abscess formation.     

Effect of a leukotriene B4 antagonist on substance P-induced granulocyte infiltration in mouse skin]

Substance P causes granulocyte (neutrophil and eosinophil) infiltration in mouse skin by inducing mast cell degranulation. However, the mediator responsible for this granulocyte infiltration has not been determined. In this study, we examined the effect of a leukotriene B4 (LTB4) antagonist ONO-4057 on substance P-induced granulocyte infiltration in the skin of BALB/c mice. Pretreatment with the LTB4 antagonist decreased substance P-induced neutrophil and eosinophil infiltrations in mouse skin at 6 h to the same extent that an inhibitor of mast cell degranulation disodium cromoglycate decreased those responses. The LTB4 antagonist also decreased substance P-induced neutrophil, but not eosinophil, infiltration in mouse skin at 24 h. We conclude that LTB4 is a major mast cell-derived chemotactic mediator for initiating substance P-induced neutrophil and eosinophil infiltrations in mouse skin.