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Specificity and function of activating Ly-49 receptors
K P Kane1, E T Silver, B Hazes
1Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada. kevin.kane@ualberta.ca
Inhibitory Ly-49 receptors allow murine natural killer (NK) cells to kill cells with aberrant class I MHC expression while sparing normal cells. This is accomplished by their recognition of specific class I MHC products and prevention of NK-cell lysis of cells that present a normal repertoire of class I MHC ligands--"the missing self hypothesis". However, Ly-49 receptors that lack the cytoplasmic immunoreceptor tyrosine-based inhibitory motif, which is required for inhibition of killing, have also been described. These receptors were found to stimulate NK killing and are therefore referred to as activating Ly-49 receptors. Interestingly, the activating receptors have class I MHC-binding domains that are nearly indistinguishable from those of the inhibiting receptors, and binding to class I MHC has now been demonstrated for three activating receptors. Presently, there is no defined physiological role for activating Ly-49 receptors. Here we present an overview of current knowledge regarding the diversity, structure and function of activating Ly-49 receptors with a focus on class I MHC specificity, and we discuss their potential role(s) in natural resistance.
Inhibitory Ly-49 receptors allow murine natural killer (NK) cells to kill cells with aberrant class I MHC expression while sparing normal cells. This is accomplished by their recognition of specific class I MHC products and prevention of NK-cell lysis of cells that present a normal repertoire of class I MHC ligands--"the missing self hypothesis". However, Ly-49 receptors that lack the cytoplasmic immunoreceptor tyrosine-based inhibitory motif, which is required for inhibition of killing, have also been described. These receptors were found to stimulate NK killing and are therefore referred to as activating Ly-49 receptors. Interestingly, the activating receptors have class I MHC-binding domains that are nearly indistinguishable from those of the inhibiting receptors, and binding to class I MHC has now been demonstrated for three activating receptors. Presently, there is no defined physiological role for activating Ly-49 receptors. Here we present an overview of current knowledge regarding the diversity, structure and function of activating Ly-49 receptors with a focus on class I MHC specificity, and we discuss their potential role(s) in natural resistance.
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