Characterization of a new monoclonal antibody (TR-19) against human transferrin receptor and its application in topographic study.

A new monoclonal antibody TR-19 (IgG2a) directed to the human transferrin receptor (CD71) was prepared after immunization of BALB/c mice with human non-T, non-B ALL cell line REH-6. This monoclonal antibody (mAb) reacted in immunofluorescence with all human cell lines tested. The reactivity with human peripheral blood leukocytes was observed only after stimulation with phytohemagglutinin (PHA). The protein precipitated by mAb TR-19 has an apparent molecular weight of 180 kDa under nonreducing and 90 kDa under reducing conditions. Sequential immunoprecipitation showed that mAb TR-19 recognizes the same antigen as the reference anti-transferrin receptor mAb OKT9. The mAb TR-19 coprecipitates the radioiodinated transferrin as a complex with its receptor. The mAb TR-19 with other three mAbs (OKT9, 5E9 and MEM-75) was used in the topographic study of the transferrin receptor. By competitive binding radioimmunoassay it was found that these mAbs recognize two distinct antigenic sites: One is specified by mAbs TR-19 and OKT9 and the second by mAbs 5E9 and MEM-75.