A murine monoclonal antibody to the IM-9 lymphoblast substance P (SP) receptor has been produced which recognizes the membrane-associated proteins of the SP receptor as demonstrated by immunoprecipitation of [125I]SP affinity-labeled and [35S]methionine biosynthetically labeled IM-9 soluble membranes. SP and anti-SP receptor binding to [35S]methionine-labeled IM-9 cell proteins were directly compared by attachment of each to affinity supports. Eluants from these affinity columns were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and revealed an equivalent 33-kDa protein in both cases. This protein corresponds to one of the previously described [125I]SP specifically affinity-labeled membrane-associated proteins. In addition, two-color fluorescence-activated cell sorter analysis with human peripheral blood T lymphocytes with fluorescein-SP and rhodamine-labeled antireceptor antibody revealed a distinct population of cells (20 to 30%) that were equally labeled by both the fluorescent peptide and antibody. This result indicates that the anti-SP receptor antibody recognizes an epitope of the receptor that is common to both human peripheral blood T lymphocytes and IM-9 lymphoblast cells.

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