Surface Marker Heterogeneity, Ligand Recognition and Proteomic Profiles of Chicken Natural Killer Cells

At day 14 of chick embryonic development (d14E) spleens are a rich source of T cell-free CD8αα⁺ cells with natural killing activity.  Immediately following isolation and after culture in the presence of recombinant chicken IL-2 (rChIL-2) CD8αα⁺, CD3ˉ d14E splenocytes display complex patterns of expression of CD8α itself and other surface markers including chB6 (Bu-1), CD1-1, NCAM, KUL01, CD5, and CD44 indicating that there is considerable heterogeneity among the CD8αα⁺ cell population.  Cytotoxicity assays revealed the capacity of rChIL-2 stimulated splenocytes to distinguish different MHC class I isoforms encoded at BF and YF MHC class I loci.  The rChIL-2 stimulated cultures also contained monocytes, which could have a role in education of the NK cells.  Mass spectrometry revealed the presence of many proteins associated with NK cell activity including the NK cell receptor 2B4.  DAVID and KEGG analyses of the proteomic data further defined the functional pathways associated with NK cell and monocyte differentiation and activation.  This study adds to the understanding of avian NK cell surface antigen expression.  It revealed an unforeseen complexity in NK cell recognition of targets and showed that a considerable number of monocytes develop alongside CD8αα⁺, CD3ˉ d14E splenic NK cells activated in vitro.  The capacity to distinguish MHC class I isoforms suggests that MHC genetics may influence early innate immune responses to infection.