LACK OF HLA CLASS I-MEDIATED INHIBITION OF NK ACTIVITY IN AN NK TRANSFECTANT EXPRESSING CD94/NKG2A IS DUE TO LOW LEVELS OF SHP-1
H. L. Chua, R. Barr, C. Zink and Z. Brahmi Department of Medicine, Indiana University School of Medicine, Indianapolis, IN.

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The regulation of NK cells is dependent upon the balance of activating and inhibitory signals transduced from its receptors such as those recognizing HLA Class I molecules. The HLA Class I receptor in humans belong to the C-type lectin group of proteins or the killer inhibitory receptors (KIR) of the immunoglobulin superfamily. Activating receptors promote NK function, whereas the inhibitory receptors, in according with the "missing-self" hypothesis block NK–mediated kill against normal autologous cells but allow the elimination of cells expressing aberrant self. Here, we investigate HLA Class-mediated inhibition in 2 transfectants, YTINDY/CD94 and YTINDY/p143 that express CD94/NKG2A or p58.2 Class I inhibitory receptors. Wild type YT-INDY is an NK-like cell line that does not express either CD94 or p58.1 inhibitory receptors. When we tested the 2 transfectants against a number of target cells expression various HLA Class I molecules, we observed that YT-INDY/p143 was readily inhibited by HLA-Cw3 but YT-INDY/CD94 was not inhibited, even by target cells expressing HLA-E, a molecule known to efficiently inhibit effector cells expressing CD94. Next, we tested the levels and enzymatic activity of SHP-1, SHP-2 and p56lck, three enzymes that transduce signals generated via CD94. SHP-1 and p56lck were barely detectable in YT-INDY and its transfectants whereas the level of SHP-2 was normal. Taken together our results demonstrate that the lack of HLA Class I inhibition in YT-INDY/CD94 is due to low SHP-1 activity but not to low p56lck activity. In addition and in contrast to what has been reported earlier, SHP-2 phosphatase does not compensate for the lack of SHP-1 activity.