Examination of the signalling properties and ligand-binding potential of stimulatory leukocyte immune-type receptors (IpLITRs) in the channel catfish (Ictalurus punctatus)

Abstract

Channel Catfish (Ictalurus punctatus, Rafinesque, 1818) leukocyte immune-type receptors (IpLITRs) are a family of proteins sharing structural and phylogenetic relationships with mammalian immune receptors. Based on their predicted signalling potential and ligand-binding properties, IpLITRs may be important in the control of immune cell effector responses in fish. The main objectives of this thesis were to determine how stimulatory IpLITRs activate cells and to develop assays for the screening of IpLITR ligands. Using cellular transfections, coimmunoprecipitation, and flow cytometry, I determined that stimulatory IpLITRs associate with specific adaptor molecules, which is required for their surface expression and signalling ability. These adaptors assemble with IpLITRs via their charged transmembrane regions and contain cytoplasmic tails encoding tyrosines that may initiate kinase pathways leading to immune cell activation. This study represents the first step towards elucidating how IpLITRs ‘turn on’ immune cells. Combined with the development of assays to identify IpLITR ligands, my work sets the stage for further investigations into the functional characterization of these receptors.