Evolving Concepts in the Roles of Galectins in Innate Immunity Open Access

Arthur, Connie Maridith (2012)

Permanent URL: https://etd.library.emory.edu/concern/etds/4b29b714s?locale=en
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Abstract


Abstract


Multiple facets of an effective immune response require efficient communication
between multiple immune factors. Much of this signaling occurs through decoding the signals of distinct carbohydrate patterns found on individual cells. Members of the galectin family of carbohydrate binding proteins play a significant role in this process. Indeed previous studies have implicated galectin family members in regulation of numerous immune functions, including immune cell turnover, immune cell proliferation, and induction of cytokine secretion. Additionally, several galectins have been implicated in the regulation of leukocyte turnover. Several members of the galectins family possess the unique ability to induce exposure of phosphatidylserine (PS) to the surface of non-apoptotic cells, thus allowing their clearance by macrophages, independent of apoptosis. Crosslinking of carbohydrate receptors by galectin family members facilitates galectin signaling. However, previous studies focused on galectins that crosslink receptors through oligomerization of a single carbohydrate recognition domain (CRD). It remained unclear however, whether tandem repeat galectin, Gal-8 which possesses two distinct CRDs, could also function in this role, and what effect multiple CRDs would have on the glycan recognition and signaling by this lectin. Additionally, recent studies have demonstrated that galectins may serve important roles in direct recognition of microbial invaders. However, given what is known about the preference of galectins for self antigens, it seems unlikely that they could serve in a traditional pattern recognition receptor (PRR) context. However, studies have shown that several bacterial species display self-like antigens on their surface that might serve to shield these bacteria from recognition by immune defenses. Given their proclivity for self antigens, galectins are uniquely poised to provide protection against these bacteria. As receptor-ligand interactions provide the fundamental basis for biological activity, we first sought to explore the carbohydrate binding specificity of Gal-4 and Gal-8. Using obtained information regarding ligand specificity, we asked whether and how this ligand specificity might impact cellular signaling and specific immunity against microbes baring self-like antigens. Taken together, these studies provide significant insight into the pivotal role of the galectin family of carbohydrate binding proteins as factors of immune protection.

Table of Contents

TABLE OF CONTENTS



Abstract Cover Page







Abstract










Cover Page









Acknowledgements








Table of Contents









List of Figures and Tables










Chapter 1: Introduction

1






Figures
10



Figure Legends
13



Chapter 2: Dimeric Galectin-8 induces phosphatidylserine exposure in leukocytes
through polylactosamine recognition by the C-terminal domain.




Introduction
15



Results


Gal-8 induces PS exposure in HL60 cells
17

Desialylation of HL60 Cells Does Not Alter Gal-8 Binding Yet Enhances

Gal-8-induced PS Exposure
18


Gal-8N and Gal-8C Fail to Induce PS Exposure in HL60 Cells
20


Gal-8 Exists as a Dimer
21


Only Gal-8NM Recognizes Cell Surface polyLacNAc Glycans
22


Gal-8 Induces PS Exposure Entirely through C-terminal Domain
24


Gal-8 Recognizes Four Primary Classes of Glycans
24


Each Gal-8 CRD Binds Distinct Classes of Glycans
25



Discussion
26



Figures
32



Figure Legends
42


Chapter 3: Signaling of PS Exposure by Gal-8 Requires Presence of Complex N-

glycans.


Introduction
47


Results


Gal-8 recognition of complex glycan structures
50


Gal-8 cell surface recognition of complex-O-glycans and glycolipids
51


Gal-8 signals through recognition of complex-N-glycans
52


Complex N glycans significantly influence glycan recognition by Gal-8C
53

Gal-8N inhibits Gal-8 signaling through recruitment away from Gal-8C

signaling domains
54







Discussion
54


Figures
58


Figure Legends
62



Chapter 4: Innate Immune Lectins Kill Pathogens Expressing Blood Group

Antigens


Introduction
64


Results


Galectins recognize blood group positive bacteria
65


Gal-4 and Gal-8 kill blood group-positive bacteria
67


Galectin killing requires blood group antigen recognition
69


Galectins specifically kill blood group positive bacteria in vivo
71




Discussion
73


Figures
75


Figure Legends
79


Chapter 5: Microbial microarray reveals complementary defense against potential

pathogens



Introduction
83


Results


Generation of a Microbial Glycan Microarray (MGM)
84


MGM analysis reveals distinct serological responses
84


MGM reveals potential targets for galectin-mediated immunity
86


In silico approach identifies novel targets of galectin-mediated immunity
88


Gal-4 and Gal-8 specifically kill bacteria
90





Discussion
91


Figures
93


Figure Legends
96



Chapter 6: Galectin-7 possesses innate killing ability towards pathogens bearing
self-like antigen




Introduction
98


Results


Gal-7 recognizes and kills blood group-positive bacteria
100


Gal-7 killing requires blood group antigen recognition
102


Gal-7 recognizes extended polymerizing O antigen preferentially 103


Gal-2 binds but does not kill blood group-positive bacteria
105

Microbial Glycan Microarray (MGM) reveals novel targets for Gal-7-

mediated immunity
106







Discussion
107


Figures
109


Figure Legends
113

Chapter 7: Summary and Future Directions
116

Materials and Methods

127

References

137





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