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Biochemical and Functional Characterization of Inhibitory Leukocyte Immune-Type Receptors in the Channel Catfish (Ictalurus punctatus) Open Access


Other title
immunoregulatory receptors
innate immunity
Ictalurus punctatus
Type of item
Degree grantor
University of Alberta
Author or creator
Montgomery, Benjamin Christian Sivert
Supervisor and department
Stafford, James (Biological Sciences)
Examining committee member and department
Barry, Michele (Medical Microbiology and Immunology)
Barreda, Daniel (Biological Sciences)
Wilson, Melanie (Microbiology)
Magor, Kathy (Biological Sciences)
Department of Biological Sciences
Physiology, Cell and Developmental Biology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
A balance of intracellular signaling events control immune cell functions. In innate immunity, many of these signals are transmitted by subsets of cell surface proteins known as immunoregulatory receptors. Through their recognition of a diverse array of molecules these receptors effectively translate extracellular cues into immune cell responses. These effector responses are vital for the elimination of pathogens and the destruction of damaged and/or infected host cells. In general, the ability of immunoregulatory receptors to promote or abrogate cellular responses is directly linked with their ability to transmit stimulatory and/or inhibitory signals. These signals are responsible for the direct immune cell-mediated elimination of pathogens, such as viruses and bacteria, and simultaneously protect healthy host tissue from autoimmune reactions. Co-expression of stimulatory and inhibitory immunoregulatory receptor-types by immune cells is common in all vertebrates but the majority of the research into understanding these complex networks has focused on mammals. Recently, it has been shown that immune cells in non-mammalian vertebrates, such as teleost (i.e. bony fish), express larger repertoires of immunoregulatory proteins but evidence as to how they are involved in mediating cellular signaling and controlling effector responses remain unknown. Channel catfish (Ictalurus punctatus) leukocyte immune-type receptors (IpLITRs) represent a large polymorphic gene family with members that possess the characteristics of putative stimulatory and inhibitory immunoregulatory proteins. The goal of my thesis work was to determine whether putative inhibitory IpLITR-types were bona fide functional receptors and to examine the signaling molecules/pathways involved in their activity. Using standard cellular transfection procedures, co-immunoprecipitations, site- directed mutagenesis, and adaptation of a vaccinia virus-based expression system for displaying IpLITRs on the surface of freshly isolated mouse natural killer (NK) cells, I discovered that two putative IpLITR-types, termed IpLITR1.2a and IpLITR1.1b, are both functional inhibitory receptors. I also determined that these IpLITRs effectively diminish cellular responses using two different mechanisms. Specifically, both IpLITR1.1b and IpLITR1.2a abrogated NK cell-mediated killing using ‘classical’ inhibitory tyrosine- based signaling motifs within their cytoplasmic regions, which recruited inhibitory phosphatases. Unlike IpLITR1.2a, IpLITR1.1b has additional tyrosine residues encoded within the membrane proximal region of its cytoplasmic tail that are not contained within known inhibitory motifs. Interestingly, one of these unique tyrosines abrogated the killing response of NK cells. However, unlike what I showed for IpLITR1.2a this was via a phosphatase-independent mechanism. These results highlight the conserved aspects of immunoregulatory receptor signaling in vertebrates while simultaneously revealing subtle nuances that may contribute towards a greater understanding of cellular effector responses.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Montgomery BC, Cortes HD, Mewes-Ares, J, Verheijen K, and Stafford JL. (2011). Teleost IgSF immunoregulatory receptors. Developmental and Comparative Immunology 35(12):1223-37.Montgomery BCS, Mewes J, Davidson C, Burshtyn DN, and Stafford JL. 2009. Cell surface expression of channel catfish leukocyte immune-type receptors (IpLITRs) and recruitment of both Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1 and SHP-2. Developmental and Comparative Immunology, 33:570-582.Montgomery BCS, Cortes, Burshtyn DN, and Stafford JL. 2012. Channel catfish leukocyte immune-type receptor mediated inhibition of cellular cytotoxicity is facilitated by SHP-1-dependent and –independent mechanisms. Developmental and Comparative Immunology, 37(1): 151-63.

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