CD8αα+MHC-II+ Cell with Capacity to Terminate Autoimmune Inflammation Is A Novel Antigen-Presenting NK-like cell in Rats

Discovery of immune tolerance mechanisms, which inhibit pre-existing autoimmune inflammation, may provide us with new strategies for treating autoimmune diseases. We have identified a CD8αα+MHC-II+ cell with professional APC capacity during our investigation on spontaneous recovery from autoimmune glomerulonephritis in a rat model. This cell actively invades inflamed target tissue to terminate an on-going autoimmune inflammation by selective killing of effector autoreactive T cells. Now, we showed that this cell used a cytotoxic machinery of Ly49s+ NK cells in killing of target T cells. Thus, this CD8αα+MHC-II+ cell, which previously was thought a professional APC, is an antigen presenting-NK (AP-NK) cell. Following its coupling with target T cells through antigen presentation, killing stimulatory receptor Ly49s6 and co-receptor CD8αα on this cell used non-classic MHC-I RT1CE16 on the target T cells as a ligand to initiate killing. Thus, activated effector T cells with elevated expression of RT1CE16 were highly susceptible to the killing by the CD8αα+ AP-NK cell. Granule cytolytic perforin/granzyme C from this cell subsequently mediated cytotoxicity, and thus, inhibition of granzyme C effectively attenuated the killing. As it can recognize and eliminate effector autoreactive T cells in the inflamed target tissue, CD8αα+ AP-NK cell not only represents a new type of immune cell involved in immune tolerance, but also is a potential candidate for developing a cell-based therapy for pre-existing autoimmune diseases. With magnetic beads methods, CD8αα+MHC-II(RT1B)+ or CD8αα+RT1Blow populations were isolated from PBL or glomeruli of immunized Wista Kyoto (WKY) or Lewis (LEW) rats. Total RNAs were isolated immediately and used for DNA microarray or other purposes. After synthesis of cDNA, an aliquot of 750 ng of amplified products was loaded onto Illumina Sentrix Beadchip Array Rat arrays, hybridized at 58ºC in an Illumina Hybridization Oven (Illumina) for 17 hours, washed and incubated with streptavidin -Cy3 to detect biotin-labeled cRNA on the arrays. Arrays were dried and scanned with BeadArray Reader (Illumina). Data were analyzed using GenomeStudio software (Illumina). Clustering and pathway analysis were performed with GenomeStudio and Ingenuity Pathway Analysis (Ingenuity Systems, Redwood City, CA) softwares respectively.