The obligate human pathogen Neisseria gonorrhoeae is responsible for the sexually transmitted disease, gonorrhea. This pathogen colonizes mucosal surfaces, and is most commonly found in the urogenital tract. The genital mucosa is comprised of various cells from epithelial to immune cells including the macrophage. Macrophages are abundant immune cells within the genital submucosa. Though the cytokine response of macrophages following N. gonorrhoeae infection is well characterized, survival of these cells following infection has not been well described. In this study, we examined the ability of N. gonorrhoeae strain FA1090B to modulate cell death in differentiated THP-1 cells (dTHP-1) and human monocyte-derived macrophages (MDMs) harvested from peripheral blood. N. gonorrhoeae was demonstrated to induce cell death in both macrophage types in a dose-dependent manner as measured at 6 hours post-stimulation. Cell death did not proceed via classical apoptosis but was associated with activation of immune caspases-1 and -4, required for the canonical and non-canonical pyroptotic pathways, respectively. MDM cell death was found to be dependent on immune caspase activity and associated with intracellular bacteria. Furthermore, caspase-4-associated MDM cell death was also observed with cytosolic N. gonorrhoeae-purified lipooligosaccharide (LOS). We did not however observe differences in the induction of pyroptosis by a penta-acylated non-immune stimulating LOS mutant strain, 1291ΔmsbB, as compared to the isogenic wild type strain 1291, or strain FA1090B. Activation of pyroptosis correlated with increased production of the pro-inflammatory mediators IL-1β, IL-6 and TNF-α. Pre-treatment of dTHP-1 cells with conditioned media from bacterial stimulated samples had little effect on N. gonorrhoeae induced cell death. Collectively, our results demonstrate that N. gonorrhoeae induces pyroptosis in human macrophages due, in part, to LOS. We postulate that N. gonorrhoeae induced pyroptosis of macrophages may partially contribute to lack of immunological memory and continual neutrophil recruitment, a hallmark of N. gonorrhoeae infection.

Francisella tularensis is the causative agent of tularemia and is categorized by the CDC as a Tier 1 select agent. This gram-negative, facultative-intracellular bacterium infects macrophages by escaping the phagosome and replicating with high efficacy in the cytosol. Multiple virulence factors, including capsule and lipopolysaccharide (LPS), are expressed by F. tularensis. Biosynthesis of capsule and LPS O-antigen requires the same O-antigen biosynthesis gene cluster and, together, expression of capsule and O-antigen confer serum resistance. Mutations in the O-antigen biosynthesis gene cluster not only result in serum sensitivity, but also attenuate the ability to cause disease in vivo. In addition to changes in F. tularensis virulence, individual capsule and O-antigen mutants appear to have distinct intracellular phenotypes in macrophages. As previously shown by Lindemann et al. (2011), the capsule and O-antigen mutants FTT1236, FTT1237, and FTT1238 all replicated in human monocyte derived macrophages (MDMs) up to 16 hr and then ceased to replicate after that. This is hypothesized to be due to MDM cytotoxicity. In contrast, Raynaud et al. (2007) showed that the capsule and O-antigen mutant wbtA completely lacked replication in J774 macrophages, the reason for which has not been identified. A potential explanation for the loss of F. tularensis capsule and O-antigen mutant replication is capture and degradation by the host cell's autophagy pathway. Capture and degradation by autophagy is an accepted innate immune response to many intracellular pathogens. When small subpopulations of bacteria that normally replicate in membrane-bound vacuoles become cytosolic, such as Mycobacterium tuberculosis and Salmonella enterica serovar Typhimurium, they are targeted to forming autophagosomes through ubiquitination and binding of autophagy receptors. Pathogens have also developed methods to circumvent recognition and degradation by autophagy. Since F. tularensis replicates in the cytosol, it stands to reason that it has a means of evading detection by autophagy. We propose that expression of capsule and O-antigen acts as a mechanism used by F. tularensis to protect itself in an extracellular environment, as well as during intracellular infection. In this thesis we characterized nine different capsule and O-antigen mutants, and found different replication phenotypes in MDMs and varying degrees of MDM cytotoxicity. Also, only a subset of the mutants was detected by the autophagy marker, ubiquitin, supporting our hypothesis that different capsule and O-antigen mutants have diverse fates in MDMs. We also show that LVS and Schu S4 wbtA mutants had similar phenotypes. Upon further evaluation, we found that LVS wbtA more readily colocalized with ubiquitin, autophagy receptors, and the autophagy membrane protein LC3B, but not Beclin-1 or LAMP-1. This supports our hypothesis that capsule and O-antigen mutants are more susceptible to recognition by autophagy. Yet, because we did not observe LAMP-1 colocalization, there may be defects in the maturation of autophagosomes to degradative autolysosomes. Finally, we found that the fate of LVS wbtA in MDMs is dissimilar from J774 macrophages, suggesting macrophage species affect mutant fate. This thesis shows that different capsule and O-antigen mutants have multiple fates in MDMs, and suggest that F. tularensis capsule and O-antigen act as protective virulence factors that limit detection by autophagy.

Tuberculosis (TB) is a critical infectious disease world-wide, and the increasing development of antibiotic resistance drives the search for effective host-directed therapies. One molecular target of potential host-directed therapy is Type 1 Interferon, (IFN-I or IFNβ), an excess of which correlates with TB progression. The mechanisms underlying IFNβ overproduction are still unclear. In this dissertation we review cellular mechanisms, including mitochondrial function and metabolism, oxidative stress, and the Integrated Stress Response, which are involved in IFNβ production and macrophage function. We also describe an experimental model of human-like TB, the B6J.C3-Sst1C3HeB/Fej Krmn (B6.Sst1S) mouse, which provides a unique and convenient system for studying mechanisms of necrosis in TB granulomas. We use primary macrophages from the B6.Sst1S mouse to establish a mechanism that links the B6.Sst1S genotype to a cascade of dysregulation that drives IFNβ superinduction and susceptibility to TB infection. TNF is necessary for granuloma formation in vivo, but in the context of transcriptional dysregulation and excess free iron, it drives oxidative stress, which amplifies IFNβ induction to pathologic levels. This induction is maintained by positive feedback through the double stranded RNA-dependent Protein Kinase (PKR). We demonstrate that interruption of this cascade by iron chelation or inhibition of lipid peroxidation attenuates IFNβ induction and improves subsequent infection outcomes. We conclude by comparing the in vitro model system to an in vivo necrotic TB granuloma, describing similarities between our system and human TB, and discussing the connections between IFN-I and autoimmune and degenerative disease and the broader application of the B6.Sst1S model system to studies of human immunity.

Recent evidence suggests that the macrophage scavenger receptor class A (SR-A, aka, CD204) plays a role in the induction of innate immune and inflammatory responses. We investigated whether SR-A will cooperate with Toll-like receptors (TLRs) in response to TLR ligand stimulation. Macrophages (J774/a) were treated with Pam2CSK4, (TLR2 ligand), Polyinosinic:polycytidylic acid (Poly I:C) (TLR3 ligand), and Lipopolysaccharides (LPS) (TLR4 ligand) for 15min in the presence or absence of fucoidan (the SR-A ligand). The levels of phosphorylated IκBα (p-IκBα) were examined by Western blot. We observed that Poly I:C and LPS alone, but not Pam2CSK4 or fucoidan increased the levels of p-IκBα. However, LPS-induced increases in p-IκBα levels were further enhanced when presence of the fucoidan. Immunoprecipitation and double fluorescent staining showed that LPS stimulation promotes SR-A association with TLR4 in the presence of fucoidan. To further confirm our observation, we isolated peritoneal macrophages from SR-A deficient (SR-A-/-), TLR4-/- and wild type (WT) mice, respectively. The peritoneal macrophages were treated with LPS for 15min in the presence and absence of fucoidan. We observed that LPS-stimulated TNFα and IL-1β production was further enhanced in the WT macrophages, but did not in either TLR4-/- or SR-A-/- macrophages, when fucoidan was present. Similarly, in the presence of fucoidan, LPS-induced IκBα phosphorylation, NF-κB binding activity, and association between TLR4 and SR-A were significantly enhanced in WT macrophages compared with LPS stimulation alone. The data suggests that SR-A is needed for LPS-induced inflammatory responses in macrophages.

In vitro studies indicate that the inflammatory response to zymosan, a fungal wall preparation, is dependent on Toll-like receptor (TLR) 2, and that this response is enhanced by the dectin-1 receptor. Complement may also play an important role in this inflammatory response. However, the relevance of these molecules within the in vivo pulmonary environment remains unknown. To examine pulmonary in vivo inflammatory responses of the lung to zymosan, zymosan was administered by intratracheal aerosolization to C57BL/6, TLR2- TLR4-, MyD88-, and complement-deficient mice. Outcomes included bronchoalveolar fluid cell counts. We next examined effects of dectin-1 inhibition on response to zymosan in alveolar macrophages in vitro and in lungs of C57BL/6, TLR2-, and complement-deficient mice. Finally, the effect of alveolar macrophage depletion on in vivo pulmonary responses was assessed. Marked zymosan-induced neutrophil responses were unaltered in TLR2-deficient mice despite a TLR2-dependent response seen with synthetic TLR2 agonists. TLR4, MyD88, and complement activation were not required for the inflammatory response to zymosan. Although dectin-1 receptor inhibition blocked the inflammatory response of alveolar macrophages to zymosan in vitro, in vivo pulmonary leukocyte recruitment was not altered even in the absence of TLR2 or complement. Depletion of alveolar macrophages did not affect the response to zymosan. Neither complement, macrophages, nor TLR2, TLR4, MyD88, and/or dectin-1 receptors were involved in the pulmonary in vivo inflammatory response to zymosan.

Zymosan is a β-glucan- and mannan-rich particle that is widely used as a cellular activator for examining the numerous responses effected by phagocytes. The macrophage mannose receptor (MR) and complement receptor 3 (CR3) have historically been considered the major macrophage lectins involved in the nonopsonic recognition of these yeast-derived particles. Using specific carbohydrate inhibitors, we show that a β-glucan receptor, but not the MR, is a predominant receptor involved in this process. Furthermore, nonopsonic zymosan binding was unaffected by genetic CD11b deficiency or a blocking monoclonal antibody (mAb) against CR3, demonstrating that CR3 was not the β-glucan receptor mediating this activity. To address the role of the recently described β-glucan receptor, Dectin-1, we generated a novel anti-Dectin-1 mAb, 2A11. Using this mAb, we show here that Dectin-1 was almost exclusively responsible for the β-glucan-dependent, nonopsonic recognition of zymosan by primary macrophages. These findings define Dectin-1 as the leukocyte β-glucan receptor, first described over 50 years ago, and resolves the long-standing controversy regarding the identity of this important molecule. Furthermore, these results identify Dectin-1 as a new target for examining the immunomodulatory properties of β-glucans for therapeutic drug design.

Glucans are fungal cell wall polysaccharides which stimulate innate immune responses. We determined the minimum unit ligand that would bind to glucan receptors on human U937 cells using laminarin-derived pentaose, hexaose, and heptaose glucan polymers. When U937 membranes were pretreated with the oligosaccharides and passed over a glucan surface, only the heptasaccharide inhibited the interaction of glucan with membrane receptors at a Kd of 31 μM (95% CI 20-48 μM) and 100% inhibition. However, the glucan heptasaccharide did not stimulate U937 monocyte NFκB signaling, nor did it increase survival in a murine model of polymicrobial sepsis. Laminarin, a larger and more complex glucan polymer (Mw=7700 g/mol), only partially inhibited binding (61±4%) at a Kd of 2.6 μM (99% CI 1.7-4.2 μM) with characteristics of a single binding site. These results indicate that a heptasaccharide is the smallest unit ligand recognized by macrophage glucan receptors. The data also indicate the presence of at least two glucan-binding sites on U937 cells and that the binding sites on human monocyte/macrophages can discriminate between glucan polymers. The heptasaccharide and laminarin were receptor antagonists, but they were not receptor agonists with respect to activation of NFκB-dependent signaling pathways or protection against experimental sepsis.

Myocardial infarction, stroke, and sepsis trigger systemic inflammation and organism-wide complications that are difficult to manage. Here, we examined the contribution of macrophages residing in vital organs to the systemic response after these injuries. We generated a comprehensive catalog of changes in macrophage number, origin, and gene expression in the heart, brain, liver, kidney, and lung of mice with myocardial infarction, stroke, or sepsis. Predominantly fueled by heightened local proliferation, tissue macrophage numbers increased systemically. Macrophages in the same organ responded similarly to different injuries by altering expression of tissue-specific gene sets. Preceding myocardial infarction improved survival of subsequent pneumonia due to enhanced bacterial clearance, which was caused by IFNɣ priming of alveolar macrophages. Conversely, EGF receptor signaling in macrophages exacerbated inflammatory lung injury. Our data suggest that local injury activates macrophages in remote organs and that targeting macrophages could improve resilience against systemic complications following myocardial infarction, stroke, and sepsis. Hoyer, Naxerova, et al. generate a comprehensive catalog of changes in macrophage number, origin, and gene expression in the heart, brain, liver, kidney, and lung of mice with myocardial infarction, stroke, or sepsis. They find that local injury activates macrophages in remote organs and that these adaptations were damaging or protective in different settings.

Macrophages are central players during atherosclerosis. Especially, macrophage cholesterol efflux, which promote the removal of free cholesterol from foam cells, are crucial to prevent lipid accumulation and reverse atherogenesis. microRNAs (miRNAs) are important regulators of various pathways involved in atherosclerosis. During inflammation, macrophages secrete extracellular vesicles (EVs) carrying miRNAs to communicate signals to nearby cells. However, the role of macrophage-derived EVs in atherogenesis is not known. In the first study, we find that EVs derived from cholesterol-loaded macrophages can inhibit macrophage migration in vitro and in vivo. This effect appears to be mediated by the transfer of several miRNAs, including miR-146a, to recipient macrophages where they repress the expression of specific pro-migratory target genes Igf2bp1 and HuR. Our studies suggest that EV-derived miRNAs secreted from atherogenic macrophages may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall. Understanding macrophage communication via EVs provided the rationale for the design of nanoparticles (NPs) that mimic macrophage EVs to deliver beneficial miRNAs to the atherosclerotic plaque. While cationic lipid/polymer-based NPs have been employed as systemic delivery vehicles of siRNA, none of these have been used to deliver miRNAs to macrophages in vivo. In the second study, we developed a chitosan NP platform for effective delivery of miRNAs to alter macrophage function in vivo. We showed that our NPs made using a cross-linked chitosan polymer can protect as well as transfer miR-33 to naïve macrophages and regulate the expression of its target gene (Abca1) as well as cholesterol efflux in vitro and in vivo. Finally, almost all miRNAs that have been characterized are efflux-repressing miRNA, thereby accelerating atherosclerosis. miR-223 is one of a few miRNAs whose overexpression can promote cholesterol efflux, modulate the inflammatory response, and thus, be antiatherogenic. However, its contribution to the pathogenesis of atherosclerosis in vivo and the mechanism underlying its effects has not been thoroughly characterized. We herein find that miR-223 is capable of suppressing plaque development via modulating cholesterol efflux and inflammatory responses, thus may serve as a potential therapeutic to reduce atherosclerosis. These effects of miR-223 appear to be dependent on the inhibition of its target gene, the transcription factor Sp3. Overall, this thesis highlights the importance of both endogenous and extracellular miRNAs in controlling different aspects of atherogenic response.

Indiana University-Purdue University Indianapolis (IUPUI) / Nanoparticles (NPs) are an emerging technology in biomedical engineering with opportunities in diagnostics, imaging, and drug delivery. NPs can be prepared from a wide range of organic and/or inorganic materials. They can be fabricated to exhibit different characteristics for biomedical applications. The goal of this thesis was to develop NPs with tunable surface properties for selective cell targeting. Specifically, polyelectrolyte complexes composed of heparin (Hep, a growth factor binding glycosaminoglycan) and poly-L-lysine (PLL, a homopolymeric lysine) were prepared via a pulse sonication method. The Hep/PLL core NPs were further layered with additional Hep, tetrazine (Tz) modified Hep, or dextran sulfate (DS). The addition of Tz handle on Hep backbone permitted easy modification of NP surface with norbornene (NB) modified motifs/ligands, including inert poly(ethylene glycol) (PEG), cell adhesive peptides (e.g., RGD), and/or fluorescent marker. Both Hep and DS coated NPs could be readily internalized by J774A.1 monocytes/macrophages, whereas PEGylated NPs effectively reduced cellular uptake/recognition. The versatility of this NP system was further demonstrated by laying DS on the Hep/PLL NP surface. DS-coated NPs were recognized by J774A.1 cells more effectively. Furthermore, DS-layered NPs seemed to reduce IL-10 production on a per cell basis, suggesting that these NPs could be used to alter polarization of macrophages.