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From the * Laboratory of Experimental Immunology, Proteins encoded by members of the Ly-49 gene family are predominantly expressed on murine natural killer (NK) cells. Several members of this gene family have been demonstrated to
inhibit NK cell lysis upon recognizing their class I ligands on target cells. In this report, we
present data supporting that not all Ly-49 proteins inhibit NK cell function. Our laboratory has
generated and characterized a monoclonal antibody (mAb) (12A8) that can be used to recognize the Ly-49D subset of murine NK cells. Transfection of Cos-7 cells with known members
of the Ly-49 gene family revealed that 12A8 recognizes Ly-49D, but also cross-reacts with the
Ly-49A protein on B6 NK cells. In addition, 12A8 demonstrates reactivity by both immunoprecipitation and two-color flow cytometry analysis with an NK cell subset that is distinct from
those expressing Ly-49A, C, or G2. An Ly-49D+ subset of NK cells that did not express Ly49A, C, and G2 was isolated and examined for their functional capabilities. Tumor targets and
concanovalin A (ConA) lymphoblasts from a variety of H2 haplotypes were examined for their
susceptibility to lysis by Ly-49D+ NK cells. None of the major histocompatibility complex
class I-bearing targets inhibited lysis of Ly-49D+ NK cells. More importantly, we demonstrate
that the addition of mAb 12A8 to Ly-49D+ NK cells can augment lysis of Fc
Intramural
Research Support Program, SAIC Frederick, National Cancer Institute-FCRDC, Frederick,
Maryland 21702-1201; § Division of Rheumatology, Washington University, St. Louis, Missouri
63110
R+ target cells in
a reverse antibody-dependent cellular cytotoxicity-type assay and induces apoptosis in Ly49D+ NK cells. Furthermore, the cytoplasmic domain of Ly-49D does not contain the V/IxYxxL immunoreceptor tyrosine-based inhibitory motif found in Ly-49A, C, or G2 that has
been characterized in the human p58 killer inhibitory receptors. Therefore, Ly-49D is the first
member of the Ly-49 family characterized as transmitting positive signals to NK cells, rather
than inhibiting NK cell function.
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