101
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Kohler S, Voß F, Gómez Mejia A, Brown JS, Hammerschmidt S. Pneumococcal lipoproteins involved in bacterial fitness, virulence, and immune evasion. FEBS Lett 2016; 590:3820-3839. [DOI: 10.1002/1873-3468.12352] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 08/01/2016] [Accepted: 08/05/2016] [Indexed: 11/07/2022]
Affiliation(s)
- Sylvia Kohler
- Department Genetics of Microorganisms; Interfaculty Institute for Genetics and Functional Genomics; University of Greifswald; Germany
| | - Franziska Voß
- Department Genetics of Microorganisms; Interfaculty Institute for Genetics and Functional Genomics; University of Greifswald; Germany
| | - Alejandro Gómez Mejia
- Department Genetics of Microorganisms; Interfaculty Institute for Genetics and Functional Genomics; University of Greifswald; Germany
| | - Jeremy S. Brown
- Department of Medicine; Centre for Inflammation and Tissue Repair; University College Medical School; London UK
| | - Sven Hammerschmidt
- Department Genetics of Microorganisms; Interfaculty Institute for Genetics and Functional Genomics; University of Greifswald; Germany
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102
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Wang E, Wang J, Long B, Wang K, He Y, Yang Q, Chen D, Geng Y, Huang X, Ouyang P, Lai W. Molecular cloning, expression and the adjuvant effects of interleukin-8 of channel catfish (Ictalurus Punctatus) against Streptococcus iniae. Sci Rep 2016; 6:29310. [PMID: 27373470 PMCID: PMC4931690 DOI: 10.1038/srep29310] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 06/13/2016] [Indexed: 01/08/2023] Open
Abstract
Interleukin-8 (IL-8) as an important cytokine involving in inflammatory and immune response, has been studied as effective adjuvants for vaccines in mammals. However, there are fewer reports about the characterization and adjuvant effects of IL-8 in fish. In this study, cloning and sequence analysis of IL-8 coding region of channel catfish (Ictalurus punctatus) were conducted, mature IL-8(rtIL-8) was expressed and evaluated for its adjuvant effects on the immunoprotection of subunit vaccine encoding α-enolase (rENO) of Streptococcus iniae from several aspects in channel catfish. The results showed co-vaccination of rENO with rtIL-8 enhanced immune responses including humoral and cellular immunity, with higher relative percent survival(RPS,71.4%) compared with the moderate RPS of rENO alone(50%) against S. iniae infection at 4 week post vaccination. While rtIL-8 failed to maintain long-lasting immune protection, only with RPS of 26.67% in rENO + rtIL-8-vaccinated fish compared with that of rENO alone(20%) at 8 week, signifying that IL-8 hold promise for use as potential immunopotentiator in vaccines against bacterial infections in fish, whereas it is insufficient to extend the immunoprotection for long time, and further studies are required to understand the mechanisms of IL-8 used as an adjuvant and seek for more effective way to strengthen the adjuvanticity of IL-8.
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Affiliation(s)
- Erlong Wang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Jun Wang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Bo Long
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Kaiyu Wang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Yang He
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Qian Yang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Defang Chen
- Department of Aquaculture, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Yi Geng
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
- Key Laboratory of Animal Disease and Human Health of Sichuan Province, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Xiaoli Huang
- Department of Aquaculture, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Ping Ouyang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
| | - Weimin Lai
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, Sichuan, China
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103
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Sunagar R, Kumar S, Franz BJ, Gosselin EJ. Vaccination evokes gender-dependent protection against tularemia infection in C57BL/6Tac mice. Vaccine 2016; 34:3396-404. [PMID: 27182819 DOI: 10.1016/j.vaccine.2016.04.054] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 04/11/2016] [Accepted: 04/19/2016] [Indexed: 11/17/2022]
Abstract
Francisella tularensis (Ft) is a Category A biothreat agent for which there currently is no FDA-approved vaccine. Thus, there is a substantial effort underway to develop an effective tularemia vaccine. While it is well established that gender can significantly impact susceptibility to primary infection, the impact of gender on vaccine efficacy is not well established. Thus, development of a successful vaccine against tularemia will require an understanding of the impact gender has on vaccine-induced protection against this organism. In this study, a role for gender in vaccine-induced protection following Ft challenge is identified for the first time. In the present study, mucosal vaccination with inactivated Ft (iFt) LVS elicited gender-based protection in C57BL/6Tac mice against respiratory challenge with Ft LVS. Specifically, vaccinated male mice were more susceptible to subsequent Ft LVS challenge. This increased susceptibility in male mice correlated with increased bacterial burden, increased tissue inflammation, and increased proinflammatory cytokine production late in post-challenge infection. In contrast, improved survival of iFt-vaccinated female mice correlated with reduced bacterial burden and enhanced levels of Ft-specific Abs in serum and broncho-alveolar lavage (BAL) fluid post-challenge. Furthermore, vaccination with a live attenuated vaccine consisting of an Ft LVS superoxide dismutase (SodB) mutant, which has proven efficacious against the highly virulent Ft SchuS4 strain, demonstrated similar gender bias in protection post-Ft SchuS4 challenge. Of particular significance is the fact that these are the first studies to demonstrate that gender differences impact disease outcome in the case of lethal respiratory tularemia following mucosal vaccination. In addition, these studies further emphasize the fact that gender differences must be a serious consideration in any future tularemia vaccine development studies.
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Affiliation(s)
- Raju Sunagar
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY 12208, United States
| | - Sudeep Kumar
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY 12208, United States
| | - Brian J Franz
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY 12208, United States
| | - Edmund J Gosselin
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, NY 12208, United States.
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104
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The role of neutrophils in inflammation resolution. Semin Immunol 2016; 28:137-45. [DOI: 10.1016/j.smim.2016.03.007] [Citation(s) in RCA: 170] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 03/11/2016] [Accepted: 03/15/2016] [Indexed: 01/29/2023]
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105
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Neonatal pneumococcal colonisation caused by Influenza A infection alters lung function in adult mice. Sci Rep 2016; 6:22751. [PMID: 26940954 PMCID: PMC4778168 DOI: 10.1038/srep22751] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 02/19/2016] [Indexed: 02/08/2023] Open
Abstract
There is emerging epidemiological data to suggest that upper respiratory tract bacterial colonisation in infancy may increase the risk of developing respiratory dysfunction later in life, and respiratory viruses are known to precipitate persistent colonisation. This study utilized a neonatal mouse model of Streptococcus pneumonia (SP) and influenza A virus (IAV) co-infection, where bronchoalveolar leukocyte infiltration had resolved by adulthood. Only co-infection resulted in persistent nasopharyngeal colonisation over 40 days and a significant increase in airway resistance in response to in vivo methacholine challenge. A significant increase in hysteresivity was also observed in IAV and co-infected mice, consistent with ventilatory heterogeneity and structural changes in the adult lung. Airway hyper-responsiveness was not associated with a detectable increase in goblet cell transdifferentiation, peribronchial smooth muscle bulk or collagen deposition in regions surrounding the airways. Increased reactivity was not observed in precision cut lung slices challenged with methacholine in vitro. Histologically, the airway epithelium appeared normal and expression of epithelial integrity markers (ZO-1, occludin-1 and E-cadherin) were not altered. In summary, neonatal co-infection led to persistent nasopharyngeal colonisation and increased airway responsiveness that was not associated with detectable smooth muscle or mucosal epithelial abnormalities, however increased hysteresivity may reflect ventilation heterogeneity.
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106
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Kara EE, McKenzie DR, Bastow CR, Gregor CE, Fenix KA, Ogunniyi AD, Paton JC, Mack M, Pombal DR, Seillet C, Dubois B, Liston A, MacDonald KPA, Belz GT, Smyth MJ, Hill GR, Comerford I, McColl SR. CCR2 defines in vivo development and homing of IL-23-driven GM-CSF-producing Th17 cells. Nat Commun 2015; 6:8644. [PMID: 26511769 PMCID: PMC4639903 DOI: 10.1038/ncomms9644] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 09/15/2015] [Indexed: 12/22/2022] Open
Abstract
IL-17-producing helper T (Th17) cells are critical for host defense against extracellular pathogens but also drive numerous autoimmune diseases. Th17 cells that differ in their inflammatory potential have been described including IL-10-producing Th17 cells that are weak inducers of inflammation and highly inflammatory, IL-23-driven, GM-CSF/IFNγ-producing Th17 cells. However, their distinct developmental requirements, functions and trafficking mechanisms in vivo remain poorly understood. Here we identify a temporally regulated IL-23-dependent switch from CCR6 to CCR2 usage by developing Th17 cells that is critical for pathogenic Th17 cell-driven inflammation in experimental autoimmune encephalomyelitis (EAE). This switch defines a unique in vivo cell surface signature (CCR6−CCR2+) of GM-CSF/IFNγ-producing Th17 cells in EAE and experimental persistent extracellular bacterial infection, and in humans. Using this signature, we identify an IL-23/IL-1/IFNγ/TNFα/T-bet/Eomesodermin-driven circuit driving GM-CSF/IFNγ-producing Th17 cell formation in vivo. Thus, our data identify a unique cell surface signature, trafficking mechanism and T-cell intrinsic regulators of GM-CSF/IFNγ-producing Th17 cells. Little is known regarding migration of Th17 cells that produce distinct cytokines implicated in protection and pathology. Kara et al. show that a switch from CCR6 to CCR2 by Th17 cells defines a signature (CCR6−CCR2+) of GM-CSF+ Th17 cells and drives pathology in a mouse model of autoimmunity.
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Affiliation(s)
- Ervin E Kara
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Duncan R McKenzie
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Cameron R Bastow
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Carly E Gregor
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Kevin A Fenix
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Abiodun D Ogunniyi
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.,Research Centre for Infectious Diseases, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - James C Paton
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.,Research Centre for Infectious Diseases, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Matthias Mack
- Department of Internal Medicine II, University Hospital Regensburg, Regensburg 93042, Germany
| | - Diana R Pombal
- Department of Microbiology and Immunology, VIB and University of Leuven, B-3000 Leuven, Belgium
| | - Cyrill Seillet
- Division of Molecular Immunology, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Bénédicte Dubois
- Department of Neurosciences, KU-Leuven-University of Leuven, B-3000 Leuven, Belgium
| | - Adrian Liston
- Department of Microbiology and Immunology, VIB and University of Leuven, B-3000 Leuven, Belgium
| | - Kelli P A MacDonald
- QIMR Berghofer Medical Research Institute, Herston, Queensland 4006, Australia
| | - Gabrielle T Belz
- Division of Molecular Immunology, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia.,Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Mark J Smyth
- QIMR Berghofer Medical Research Institute, Herston, Queensland 4006, Australia.,School of Medicine, University of Queensland, Herston, Queensland 4006, Australia
| | - Geoffrey R Hill
- QIMR Berghofer Medical Research Institute, Herston, Queensland 4006, Australia.,The Royal Brisbane and Women's Hospital, Herston, Queensland 4029, Australia
| | - Iain Comerford
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Shaun R McColl
- Department of Molecular and Cellular Biology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia.,Centre for Molecular Pathology, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
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107
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Immune ageing and susceptibility to Streptococcus pneumoniae. Biogerontology 2015; 17:449-65. [DOI: 10.1007/s10522-015-9614-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Accepted: 10/05/2015] [Indexed: 12/16/2022]
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108
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Immunodominant epitope-specific Th1 but not Th17 responses mediate protection against Helicobacter pylori infection following UreB vaccination of BALB/c mice. Sci Rep 2015; 5:14793. [PMID: 26434384 PMCID: PMC4593181 DOI: 10.1038/srep14793] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Accepted: 09/09/2015] [Indexed: 12/13/2022] Open
Abstract
Helicobacter pylori (H. pylori) infects more than half of the world’s population, causing chronic gastritis, peptic ulcers and gastric cancer. Urease B subunit (UreB), a conserved protein of H. pylori, is capable of inducing specific CD4+ T-cell responses and provides protection against this infection. Previous studies have confirmed the effectiveness of rUreB subunit vaccines in generating CD4+ T-cell-mediated protection, but less is known regarding the roles of different subtypes of T-cell immunity, such as Th1, Th2 and Th17, particularly the immunodominant epitopes inducing specific CD4+ T-cell responses, in vaccine-mediated protection. In this study, we demonstrated that the vaccination of BALB/c mice with rUreB resulted in significant antigen-specific Th1 and Th17 immune responses. Importantly, two novel Th epitopes, UreB317–329 and UreB409–421, which are recognized by a major population of CD4+ T cells, were identified in immunized mice. Our results demonstrated that two novel epitopes can simultaneously induce Th1 and Th17 immune responses; however, only the epitope vaccine-induced CD4+ T-cells secreting IFN-γ mediated the protection against H. pylori; cells secreting IL-17A did not. Taken together, our results suggest that two novel immunodominant epitopes can induce Th1 and Th17 immune responses, but only the induced Th1 lymphocytes mediate protection against H. pylori.
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109
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110
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Sanfilippo AM, Furuya Y, Roberts S, Salmon SL, Metzger DW. Allergic Lung Inflammation Reduces Tissue Invasion and Enhances Survival from Pulmonary Pneumococcal Infection in Mice, Which Correlates with Increased Expression of Transforming Growth Factor β1 and SiglecF(low) Alveolar Macrophages. Infect Immun 2015; 83:2976-83. [PMID: 25964474 PMCID: PMC4468552 DOI: 10.1128/iai.00142-15] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Accepted: 05/04/2015] [Indexed: 11/20/2022] Open
Abstract
Asthma is generally thought to confer an increased risk for invasive pneumococcal disease (IPD) in humans. However, recent reports suggest that mortality rates from IPD are unaffected in patients with asthma and that chronic obstructive pulmonary disease (COPD), a condition similar to asthma, protects against the development of complicated pneumonia. To clarify the effects of asthma on the subsequent susceptibility to pneumococcal infection, ovalbumin (OVA)-induced allergic lung inflammation (ALI) was induced in mice followed by intranasal infection with A66.1 serotype 3 Streptococcus pneumoniae. Surprisingly, mice with ALI were significantly more resistant to lethal infection than non-ALI mice. The heightened resistance observed following ALI correlated with enhanced early clearance of pneumococci from the lung, decreased bacterial invasion from the airway into the lung tissue, a blunted inflammatory cytokine and neutrophil response to infection, and enhanced expression of transforming growth factor β1 (TGF-β1). Neutrophil depletion prior to infection had no effect on enhanced early bacterial clearance or resistance to IPD in mice with ALI. Although eosinophils recruited into the lung during ALI appeared to be capable of phagocytizing bacteria, neutralization of interleukin-5 (IL-5) to inhibit eosinophil recruitment likewise had no effect on early clearance or survival following infection. However, enhanced resistance was associated with an increase in levels of clodronate-sensitive, phagocytic SiglecF(low) alveolar macrophages within the airways following ALI. These findings suggest that, while the risk of developing IPD may actually be decreased in patients with acute asthma, additional clinical data are needed to better understand the risk of IPD in patients with different asthma phenotypes.
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Affiliation(s)
- Alan M Sanfilippo
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA
| | - Yoichi Furuya
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA
| | - Sean Roberts
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA
| | - Sharon L Salmon
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA
| | - Dennis W Metzger
- Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, USA
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111
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José RJ, Williams AE, Mercer PF, Sulikowski MG, Brown JS, Chambers RC. Regulation of neutrophilic inflammation by proteinase-activated receptor 1 during bacterial pulmonary infection. THE JOURNAL OF IMMUNOLOGY 2015; 194:6024-34. [PMID: 25948816 PMCID: PMC4456635 DOI: 10.4049/jimmunol.1500124] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 04/06/2015] [Indexed: 12/24/2022]
Abstract
Neutrophils are key effector cells of the innate immune response to pathogenic bacteria, but excessive neutrophilic inflammation can be associated with bystander tissue damage. The mechanisms responsible for neutrophil recruitment to the lungs during bacterial pneumonia are poorly defined. In this study, we focus on the potential role of the major high-affinity thrombin receptor, proteinase-activated receptor 1 (PAR-1), during the development of pneumonia to the common lung pathogen Streptococcus pneumoniae. Our studies demonstrate that neutrophils were indispensable for controlling S. pneumoniae outgrowth but contributed to alveolar barrier disruption. We further report that intra-alveolar coagulation (bronchoalveolar lavage fluid thrombin-antithrombin complex levels) and PAR-1 immunostaining were increased in this model of bacterial lung infection. Functional studies using the most clinically advanced PAR-1 antagonist, SCH530348, revealed a key contribution for PAR-1 signaling in influencing neutrophil recruitment to lung airspaces in response to both an invasive and noninvasive strain of S. pneumoniae (D39 and EF3030) but that PAR-1 antagonism did not impair the ability of the host to control bacterial outgrowth. PAR-1 antagonist treatment significantly decreased pulmonary levels of IL-1β, CXCL1, CCL2, and CCL7 and attenuated alveolar leak. Ab neutralization studies further demonstrated a nonredundant role for IL-1β, CXCL1, and CCL7 in mediating neutrophil recruitment in response to S. pneumoniae infection. Taken together, these data demonstrate a key role for PAR-1 during S. pneumoniae lung infection that is mediated, at least in part, by influencing multiple downstream inflammatory mediators.
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Affiliation(s)
- Ricardo J José
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
| | - Andrew E Williams
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
| | - Paul F Mercer
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
| | - Michal G Sulikowski
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
| | - Jeremy S Brown
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
| | - Rachel C Chambers
- Centre for Inflammation and Tissue Repair, University College London, London WC1E 6JF, United Kingdom
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112
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Importance of bacterial replication and alveolar macrophage-independent clearance mechanisms during early lung infection with Streptococcus pneumoniae. Infect Immun 2015; 83:1181-9. [PMID: 25583525 DOI: 10.1128/iai.02788-14] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Although the importance of alveolar macrophages for host immunity during early Streptococcus pneumoniae lung infection is well established, the contribution and relative importance of other innate immunity mechanisms and of bacterial factors are less clear. We have used a murine model of S. pneumoniae early lung infection with wild-type, unencapsulated, and para-amino benzoic acid auxotroph mutant TIGR4 strains to assess the effects of inoculum size, bacterial replication, capsule, and alveolar macrophage-dependent and -independent clearance mechanisms on bacterial persistence within the lungs. Alveolar macrophage-dependent and -independent (calculated indirectly) clearance half-lives and bacterial replication doubling times were estimated using a mathematical model. In this model, after infection with a high-dose inoculum of encapsulated S. pneumoniae, alveolar macrophage-independent clearance mechanisms were dominant, with a clearance half-life of 24 min compared to 135 min for alveolar macrophage-dependent clearance. In addition, after a high-dose inoculum, successful lung infection required rapid bacterial replication, with an estimated S. pneumoniae doubling time of 16 min. The capsule had wide effects on early lung clearance mechanisms, with reduced half-lives of 14 min for alveolar macrophage-independent and 31 min for alveolar macrophage-dependent clearance of unencapsulated bacteria. In contrast, with a lower-dose inoculum, the bacterial doubling time increased to 56 min and the S. pneumoniae alveolar macrophage-dependent clearance half-life improved to 42 min and was largely unaffected by the capsule. These data demonstrate the large effects of bacterial factors (inoculum size, the capsule, and rapid replication) and alveolar macrophage-independent clearance mechanisms during early lung infection with S. pneumoniae.
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