Kaushik Chakrabarty

Bacillus anthracis spores stimulate cytokine and chemokine innate immune responses in human alveolar macrophages through multiple mitogen-activated protein kinase pathways.

ABSTRACT Contact with the human alveolar macrophage plays a key role in the innate immune response to Bacillus anthracis spores. Because there is a significant delay between the initial contact of the spore with the host and clinical evidence of disease, there appears to be temporary containment of the pathogen by the innate immune system. Therefore, the early macrophage response to Bacillus anthracis exposure is important in understanding the pathogenesis of this disease. In this paper, we studied the initial events after exposure to spores, beginning with the rapid internalization of spores by the macrophages. Spore exposure rapidly activated the mitogen-activated protein kinase signaling pathways extracellular signal-regulated kinase, c-Jun-NH2-terminal kinase, and p38. This was followed by the transcriptional activation of cytokine and primarily monocyte chemokine genes as determined by RNase protection assays. Transcriptional induction is reflected at the translational level, as interleukin-1α (IL-1α), IL-1β, IL-6, and tumor necrosis factor alpha (TNF-α) cytokine protein levels were markedly elevated as determined by enzyme-linked immunosorbent assay. Induction of IL-6 and TNF-α, and, to a lesser extent, IL-1α and IL-1β, was partially inhibited by the blockade of individual mitogen-activated protein kinases, while the complete inhibition of cytokine induction was achieved when multiple signaling pathway inhibitors were used. Taken together, these data clearly show activation of the innate immune system in human alveolar macrophages by Bacillus anthracis spores. The data also show that multiple signaling pathways are involved in this cytokine response. This report is the first comprehensive examination of this process in primary human alveolar macrophages.

Bacillus anthracis Peptidoglycan Stimulates an Inflammatory Response in Monocytes through the p38 Mitogen-Activated Protein Kinase Pathway

We hypothesized that the peptidoglycan component of B. anthracis may play a critical role in morbidity and mortality associated with inhalation anthrax. To explore this issue, we purified the peptidoglycan component of the bacterial cell wall and studied the response of human peripheral blood cells. The purified B. anthracis peptidoglycan was free of non-covalently bound protein but contained a complex set of amino acids probably arising from the stem peptide. The peptidoglycan contained a polysaccharide that was removed by mild acid treatment, and the biological activity remained with the peptidoglycan and not the polysaccharide. The biological activity of the peptidoglycan was sensitive to lysozyme but not other hydrolytic enzymes, showing that the activity resides in the peptidoglycan component and not bacterial DNA, RNA or protein. B. anthracis peptidoglycan stimulated monocytes to produce primarily TNFα; neutrophils and lymphocytes did not respond. Peptidoglycan stimulated monocyte p38 mitogen-activated protein kinase and p38 activity was required for TNFα production by the cells. We conclude that peptidoglycan in B. anthracis is biologically active, that it stimulates a proinflammatory response in monocytes, and uses the p38 kinase signal transduction pathway to do so. Given the high bacterial burden in pulmonary anthrax, these findings suggest that the inflammatory events associated with peptidoglycan may play an important role in anthrax pathogenesis.

Human Lung Innate Immune Response to Bacillus anthracis Spore Infection

ABSTRACT Bacillus anthracis, the causative agent of inhalational anthrax, enters a host through the pulmonary system before dissemination. We have previously shown that human alveolar macrophages participate in the initial innate immune response to B. anthracis spores through cell signal-mediated cytokine release. We proposed that the lung epithelia also participate in the innate immune response to this pathogen, and we have developed a human lung slice model to study this process. Exposure of our model to B. anthracis (Sterne) spores rapidly activated the mitogen-activated protein kinase signaling pathways ERK, p38, and JNK. In addition, an RNase protection assay showed induction of mRNA of several cytokines and chemokines. This finding was reflected at the translational level by protein peak increases of 3-, 25-, 9-, 34-, and 5-fold for interleukin-6 (IL-6), tumor necrosis factor alpha, IL-8, macrophage inflammatory protein 1α/β, and monocyte chemoattractant protein 1, respectively, as determined by an enzyme-linked immunosorbent assay. Inhibition of individual pathways by UO126, SP600125, and SB0203580 decreased induction of chemokines and cytokines by spores, but this depended on the pathways inhibited and the cytokines and chemokines induced. Combining all three inhibitors reduced induction of all cytokines and chemokines tested to background levels. An immunohistochemistry analysis of IL-6 and IL-8 revealed that alveolar epithelial cells and macrophages and a few interstitial cells are the source of the cytokines and chemokines. Taken together, these data showed the activation of the pulmonary epithelium in response to B. anthracis spore exposure. Thus, the lung epithelia actively participate in the innate immune response to B. anthracis infection through cell signal-mediated elaboration of cytokines and chemokines.

Resistance of Human Alveolar Macrophages to Bacillus anthracis Lethal Toxin

The etiologic agent of inhalational anthrax, Bacillus anthracis, produces virulence toxins that are important in the disease pathogenesis. Current studies suggest that mouse and human macrophages are susceptible to immunosuppressive effects of one of the virulence toxins, lethal toxin (LT). Thus a paradigm has emerged that holds that the alveolar macrophage (AM) does not play a significant role in the innate immune response to B. anthracis or defend against the pathogen as it is disabled by LT. This is inconsistent with animal models and autopsy studies that show minimal disease at the alveolar surface. We examined whether AM are immunosuppressed by LT. We found that human AM were relatively resistant to LT-mediated innate immune cytokine suppression, MEK cleavage, and induction of apoptosis as compared with mouse RAW 264.7 macrophages. Mouse AM and murine bone marrow-derived macrophages were also relatively resistant to LT-mediated apoptosis despite intermediate sensitivity to MEK cleavage. The binding component of LT, protective Ag, does not attach to human AM, although it did bind to mouse AM, murine bone marrow-derived macrophages, and RAW 264.7 macrophages. Human AM do not produce significant amounts of the protective Ag receptor anthrax toxin receptor 1 (TEM8/ANTXR1) and anthrax toxin receptor 2 (CMG2/ANTXR2). Thus, mature and differentiated AM are relatively resistant to the effects of LT as compared with mouse RAW 264.7 macrophages. AM resistance to LT may enhance clearance of the pathogen from the alveolar surface and explain why this surface is relatively free of B. anthracis in animal models and autopsy studies.

Gene expression profiling of human alveolar macrophages infected by B. anthracis spores demonstrates TNF-α and NF-κb are key components of the innate immune response to the pathogen

BackgroundBacillus anthracis, the etiologic agent of anthrax, has recently been used as an agent of bioterrorism. The innate immune system initially appears to contain the pathogen at the site of entry. Because the human alveolar macrophage (HAM) plays a key role in lung innate immune responses, studying the HAM response to B. anthracis is important in understanding the pathogenesis of the pulmonary form of this disease.MethodsIn this paper, the transcriptional profile of B. anthracis spore-treated HAM was compared with that of mock-infected cells, and differentially expressed genes were identified by Affymetrix microarray analysis. A portion of the results were verified by Luminex protein analysis.ResultsThe majority of genes modulated by spores were upregulated, and a lesser number were downregulated. The differentially expressed genes were subjected to Ingenuity Pathway analysis, the Database for Annotation, Visualization and Integrated Discovery (DAVID) analysis, the Promoter Analysis and Interaction Network Toolset (PAINT) and Oncomine analysis. Among the upregulated genes, we identified a group of chemokine ligand, apoptosis, and, interestingly, keratin filament genes. Central hubs regulating the activated genes were TNF-α, NF-κB and their ligands/receptors. In addition to TNF-α, a broad range of cytokines was induced, and this was confirmed at the level of translation by Luminex multiplex protein analysis. PAINT analysis revealed that many of the genes affected by spores contain the binding site for c-Rel, a member of the NF-κB family of transcription factors. Other transcription regulatory elements contained in many of the upregulated genes were c-Myb, CP2, Barbie Box, E2F and CRE-BP1. However, many of the genes are poorly annotated, indicating that they represent novel functions. Four of the genes most highly regulated by spores have only previously been associated with head and neck and lung carcinomas.ConclusionThe results demonstrate not only that TNF-α and NF-κb are key components of the innate immune response to the pathogen, but also that a large part of the mechanisms by which the alveolar macrophage responds to B. anthracis are still unknown as many of the genes involved are poorly annotated.

Regulation of the prostaglandin enzymatic system by estradiol and progesterone in nonpregnant sheep cervix.

In the present study, we examined the in vivo effects of estradiol (E(2)) and progesterone on cyclooxygenase (COX) 2, prostaglandin F synthase (PTGFS, also known as PGFS), and membrane-associated prostaglandin E synthase 1 (mPTGES1) expression at both mRNA and protein levels using a nonpregnant ovariectomized (OVX) sheep model. Sixteen ewes were OVX shortly after ovulation. After 40 days, ewes were treated with saline (Cont, n=5), or E(2) infused intravenously for 2 days (50 microg/day, n=5) or intravaginal progesterone (P) sponges for 10 days (0.3 g P, n=6). Cervical COX2, PTGFS, and mPTGES1 mRNA and protein were quantified by northern and western blot analyses respectively. In situ hybridization and/or immunocytochemistry were used to localize the cellular distribution of COX2, PTGFS, and mPTGES1 mRNAs and proteins. COX2 mRNA abundance increased significantly in the cervix after E(2) treatment (P<0.05). However, progesterone was a more potent stimulator than E(2) of COX2 mRNA and protein abundance in the cervix (P<0.01). In contrast, PTGFS and mPTGES1 mRNA and protein concentrations did not change after E(2) or progesterone treatment (P>0.05). COX2, PTGFS, and mPTGES1 mRNA and protein were only localized in cervical glandular epithelial cells. This study shows that increased cervical COX2 mRNA and protein, but not PTGFS and mPTGES1 mRNA and protein, were associated with E(2) and progesterone treatment in nonpregnant sheep. More strikingly, progesterone was a more potent stimulator of cervical COX2 expression than E(2). The expression of COX2, PTGFS, and mPTGES1 mRNA and/or protein was confined in the cervical glandular epithelial cells of nonpregnant sheep.

Sufficient Progesterone-Priming Prior to Estradiol Stimulation Is Required for Optimal Induction of the Cervical Prostaglandin System in Pregnant Sheep at 0.7 Gestations

Abstract The purposes of this study were to determine the separate and interactive functions of progesterone and estradiol in regulating the cervical prostaglandin (PG) system in pregnant sheep at 0.7 gestations. At 106–108 days of gestational age (dGA), ewes were treated with vehicle for 14 days (n = 5) or vehicle for 12 days followed by estradiol 5 mg twice a day, intramuscularly for 2 days (n = 5) or progesterone 100 mg, twice a day, intramuscularly for 14 days (n = 5) or progesterone 100 mg twice a day, intramuscularly for 10 days and then 2 days vehicle followed by estradiol 5 mg twice a day intramuscularly for 2 days (n = 5). At 121–123 dGA, cervical tissues were obtained under halothane anesthesia. Cervical RNA and protein were extracted and analyzed for prostaglandin-endoperoxide synthase 2 (COX2), two PGE2 receptors, PTGER2 and PTGER4, and estrogen receptor alpha (ESR1) by Northern and Western blot analysis. Immunocytochemistry and in situ hybridization were applied to localize cellular distribution of COX2, PTGER2, and PTGER4 in the cervix. Data were analyzed by ANOVA. COX2 and PTGER4 mRNAs and proteins were increased (P < 0.05) in ewes treated with combined estradiol and progesterone but not in ewes treated with estradiol or progesterone alone compared with controls. ESR1 mRNA was increased in ewes treated with progesterone and estradiol plus progesterone. In contrast, PTGER2 mRNA and protein remained the same after all treatments. COX2 mRNA and protein were localized only in cervical glandular epithelial cells, whereas PTGER2 and PTGER4 were localized in both cervical glandular epithelial and smooth muscle cells. In conclusion, these data suggest that additional progesterone priming at 0.7 gestations synergizes with estradiol to induce cervical COX2, PTGER4, and ESR1 and support our hypothesis that stimulation of the cervical PG system by estradiol is optimized by sufficient progesterone priming in the pregnant sheep cervix.

36 BACILLUS ANTHRACIS SPORES STIMULATE CYTOKINE AND CHEMOKINE INNATE IMMUNE RESPONSES IN HUMAN ALVEOLAR MACROPHAGES THROUGH MULTIPLE MAPK PATHWAYS.

Contact with the human alveolar macrophage plays a key role in the innate immune response to Bacillus anthracis spores. Because there is a significant delay between the initial contact of the spore with the host and clinical evidence of disease, there appears to be temporary containment of the pathogen by the innate immune system. Therefore, the early macrophage response to anthrax exposure is important in understanding the pathogenesis of this disease. We examined the initial events after exposure of human alveolar macrophages obtained by bronchoscopy to Bacillus anthracis (Sterne) spores. Spores were rapidly internalized as determined by confocal microscopy. Spore exposure also rapidly activated the MAPK signaling pathways ERK, JNK, and P38. This was followed by transcriptional activation of cytokine and primarily monocyte chemokine genes as determined by RNase protection assays. Transcriptional induction was reflected at the translational level as IL-1a and b, IL-6, and TNF-a cytokine protein levels were markedly elevated as determined by ELISA. Induction of IL-6 and TNF-a, and to a lesser extent IL-1a and -b, was partially inhibited by blockade of individual mitogen-activated protein kinases, while complete inhibition of cytokine induction was achieved when multiple signaling pathway inhibitors were used. Taken together, these data clearly show activation of the innate immune system in human alveolar macrophages by Bacillus anthracis spores. The data also show that multiple signaling pathways are involved in this cytokine response.