Abstract: An isolated polynucleotide encodes JAK-3 protein. JAK-3 protein is a protein tyrosine kinase having a molecular weight of approximately 125 kDa which has tandem non-identical catalytic domains, lacks SH2 or SH3 domains, and is expressed in NK cells and stimulated or transformed T cells, but not in resting T cells. The protein itself and antibodies to this protein are also presented. Further, methods of identifying therapeutic agents for modulating the immune system make use of the foregoing.

Abstract: The invention provides isolated nucleic acids molecules, designated TLT-1 nucleic acid molecules, which encode novel inhibitory receptors expressed on platelets. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing TLT-1 nucleic acid molecules, host cells into which the expression vectors have been introduced, and nonhuman transgenic animals in which a TLT-1 gene has been introduced or disrupted. The invention still further provides isolated TLT-1 proteins, fusion proteins, antigenic peptides and anti-TLT-1 antibodies. Diagnostic methods utilizing compositions of the invention are also provided.