In order to obtain an anti-interleukin 2 (IL 2) receptor antibody, we immunized mice with phorbol myristate acetate-pulsed rat T lymphoblasts. The spleen cells of the mice were fused with myeloma cells. Several stable clones of hybridoma cells were obtained that produced monoclonal antibodies (mAb) reacting specifically with rat T lymphoblasts. Only one of these mAb, the mAb ART18, showed characteristics of a putative anti-IL 2 receptor antibody. This mAb was produced on a large scale,

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... and characterized. As tested by a binding assay, 125I-labeled mAb ART18 bound to rat T lymphoblasts (7.5 X 10(4) binding sites per cell), but not to thymocytes or spleen cells of rat origin, or to lymphoblasts, thymocytes, or spleen cells of murine origin. Only marginal binding to lipopolysaccharide-stimulated rat lymphoblasts was detected. The mAb ART18 inhibited in a species-specific and dose-dependent manner i) the capacity of rat T lymphoblasts to absorb IL 2 activity and ii) the capacity of rat T lymphoblasts to proliferate in response in IL 2. The function of T lymphoblasts of murine origin was not affected by the mAb ART18. The time course of the acquisition by mitogen-stimulated spleen cells of the capacity to absorb IL 2 activity was paralleled by that of their capacity to bind 125I-labeled mAb ART18. According to these data, the mAb ART18 seems to be directed against an antigenic determinant of the IL 2 receptor molecule.