Mouse gp49B is a member of the leukocyte immunoglobulin-like receptor family. It is constitutively expressed by mast cells and certain myeloid cells, and expression can be induced on natural killer (NK) cells and T cells. We have cloned several rat cDNA, 78% identical to mouse gp49B at the amino acid level, that represent the rat orthologue to mouse gp49B. A mouse monoclonal antibody (WEN29) against rat gp49B was generated. By flow cytometry and Northern blot analysis, gp49B was found to be expressed by neutrophils and monocytes, but not NK cells (primary or IL-2-activated), T cells (resting or concanavalin A-stimulated) or peritoneal mast cells. Following pervanadate treatment, the tyrosine phosphatase SHP-1 was co-immunoprecipitated with gp49B in the macrophage cell line R2. In glutathione S-transferase pull-down experiments, the cytoplasmic tail of rat gp49B associated with the SH2 domains of both SHP-1 and SHP-2, dependent on intact and phosphorylated immunoreceptor tyrosine-based inhibition motifs (ITIM). Compared to mouse, the cytoplasmic domain of rat gp49B contains a third ITIM-like sequence (YLYASV) that was phosphorylated by several Src family tyrosine kinases, enhanced the phosphorylation of other ITIM, and bound to the SH2 domains of SHP-2, suggesting a role in the recruitment of downstream phosphatases.