A new family of immunoreceptor molecules of the immunoglobulin superfamily, (LIR) polypeptides is described. Disclosed are sequences encoding LIR family members and their deduced amino acid sequences, polypeptides encoded by DNA that hybridize to oligonucleotide probes having defined sequences, processes for producing polypeptides of the LIR family, and antagonistic antibodies to LIR family members. LIR family members can be used to treat autoimmune diseases and disease states associated with suppressed immune function.