Mechanisms of Acute Inflammatory Control by Phagocytes

• Author / Creator

  Rieger, Aja M

• Phagocytosis is an important, evolutionarily conserved mechanism integral to immune defense and homeostasis. Phagocytosis is initiated by the interaction of receptors on the surface of phagocytes with ligands on large particles, generally over 1 μm. Receptor ligation results in actin polymerization, which subsequently leads to particle internalization. The main objective of my thesis research was to characterize functional phagocytic responses at inflammatory sites, where various responses are involved in the clearance of pathogens, dying or senescent cells, and in tissue repair/ wound healing. While this balance is well understood in mammals, much less is known in lower vertebrates. In accordance with mammals, I found that differentiation along the macrophage pathway resulted in increases in phagocytic capacity, with mature macrophage having the greatest capacity. Interestingly, activation resulted in differential regulation of phagocytosis in monocytes and mature macrophages. Within these subsets there was also differential regulation of phagolysosome fusion and the production of reactive oxygen species (ROS). The activation of specific phagocytic responses at distinct stages of differentiation suggests that these responses may allow specialization of host immunity requirements within specialized niches. When phagocytic responses to inflammatory or homeostatic responses were studied, I found that teleost fish displayed divergent responses following phagocytosis, which is consistent with observations in mice. However, I found significant differences between these species with regards to the level of responsiveness to zymosan and apoptotic bodies, the identity of infiltrating leukocytes, their rate of infiltration, and the kinetics and strength of resulting antimicrobial responses. The primary differences were noted in the neutrophilic responses. Importantly, I found that activated murine, but not teleost, neutrophils possess the capacity to internalize apoptotic cells, resulting in decreased neutrophil ROS production. This may play an important part in the recently identified anti-inflammatory activity that mammalian neutrophils display during the resolution phase of inflammation. Goldfish responses were partially regulated by soluble factors. However, no changes were noted in canonical mammalian factors, leading to identification of a novel role for a unique teleost receptor- soluble colony stimulating factor-1 receptor (sCSF-1R). Soluble CSF-1 receptor was originally described as a regulator of macrophage proliferation. Soluble CSF-1R is highly upregulated following interaction with apoptotic cells, resulting in reduced cellular infiltration, phagocytosis, ROS production, expression of pro-inflammatory factors, and downstream antimicrobial responses. The effects sCSF-1R mirrored several of those induced by apoptotic cells, suggesting that sCSF-1R may be a central player in the regulation of anti-inflammatory responses induced by apoptotic cells. These observations were then applied to the study of an Aeromonas infection. Aeromonas is a highly virulent fish pathogen with devastating effects on the fish farming industry. It has been previously shown that increases in the production of reactive intermediates by host immune cells cause significant cytotoxicity at the infection site, but have limited protective effects against this catalase-producing bacterium. I found that Aeromonas veronii infection promotes systemic expression of sCSF-1R. However, unlike other pathogen models, sCSF-1R was unable to inhibit inflammation at the A. veronii challenge site and had no impact on the production of ROS in vitro or in vivo. Importantly though, I found that the increased systemic expression of sCSF-1R in A. veronii infected fish appears to decrease proliferative activity among cells in the hematopoietic compartment, which is further coupled to a decrease in CSF-1 expression in kidney hematopoietic tissues. Overall, the data presented here places the CSF-1 system and its regulator sCSF-1R at the center of both the induction and regulation of inflammation in teleost fish, with the effects of this system impacting the macrophage-lineage cells as well as the neutrophilic and potentially lymphocytic cells.

• Subjects / Keywords

  • Macrophages
  • Goldfish
  • Phagocytosis
  • SCSR-1R

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3GX4517X

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.