NONCLASSICAL LEUKOCYTE IMMUNE-TYPE RECEPTORS IN CHANNEL CATFISH, ICTALURUS PUNCTATUS
Jonathan Crider, University of Mississippi Medical Center
Jonathan D. Crider, Laura Blackmon, Melanie Wilson, PhD, Eva Bengtén, PhD
Department of Microbiology and Immunology, University of Mississippi Medical Center, Jackson, MS
The Leukocyte Immune-Type Receptor (LITR) family consists of activating and inhibitory immunoregulatory receptors and is unique to teleosts. Family members vary in their number of immunoglobulin (Ig) domains, which are phylogenetically related to both Fc receptors and to receptors encoded within the leukocyte receptor complex. Previously, it was thought that all LITRs shared similar D1 and D2 Ig-domains, however we recently identified a subset that lacked these domains. One member of this nonclassical LITR subset, LITR622, contains eight Ig-domains beginning with a unique D1 that exhibits <42% amino acid identity with classical D1 domains. The LITR622 gene also encodes a distinct signal peptide and a D3 Ig domain specific to this subset. Using a combination of Southern blot and genomic sequencing we predict there are 13 copies of this D3 exon in the catfish haploid genome. That a subset of CC41 mAb-reactive LITRs, expressed on catfish TS32.15 CTLs and NK cells, was upregulated in catfish during an anti-channel catfish virus (CCV) response, led us to investigate LITR622 gene expression in CCV-infected cells. Clonal G14D T cells were infected with CCV (MOI of 10) and total RNA was isolated from mock- and CCV-infected cells at 3hr, 5hr and 7hr post-infection. This time course confirmed that LITR622 gene expression was dependent upon viral replication, and poly(I:C) treatment also stimulated expression of LITR622. Such findings may indicate that some LITR622 proteins function as stress molecules which are recognized by certain “more classical” LITRs and further demonstrates the complexity of the LITR gene family.