Cloning of rat homologues of the murine 2B4 NK cell receptor

2B4 is a 66 kDa monomer expressed on the surface of all murine NK cells and the subset of T cells able to mediate NK cell like cytotoxicity. Functional studies indicate that ligation of 2B4 transduces activation signals and is associated with increased target cell lysis and cytokine secretion. Characterization of cDNA clones has shown 2B4 to be a member of the Ig superfamily, that structurally resembles CD2, CD48 and LFA-3. Alternative splicing produces 2 variants of 2B4, both of which are expressed in murine NK cells and which differ only at the 3′ region of the cytoplasmic domain. Here we describe the cloning of the extracellular domains of the rat homologue to murine 2B4 by RT-PCR from the RNK-16 cell line. Surprisingly, 2 homologous sequences were obtained. Designated rat 2B4-A and rat 2B4-B, the deduced amino acid sequences share approximately 80% identity with murine 2B4 and 94% identity with each other. A short region of sequence divergence between the 2 rat 2B4 genes was used to generate two 19 amino acid peptide antigens, one each for rat 2B4-A and 2B4-B. Rabbit antisera were generated against these peptide antigens. RNK-16 cells stain by FACS analysis with postimmune sera, but not with preimmune sera. Immunoprecipitation of surface labeled RNK-16 cells with rat 2B4-A antisera identifies an approximately 60 kDa protein, which when deglycosolated is approximately 40 kDa. These protein sizes are similar to the murine 2B4.