The Journal of Immunology, Vol 129, Issue 5 2287-2292, Copyright © 1982 by American Association of Immunologists

ARTICLES

Antibody affinity may influence antigenic modulation of the common acute lymphoblastic leukemia antigen in vitro

TW Lebien, DR Boue, JG Bradley and JH Kersey

We have produced a new monoclonal antibody designated BA-3. An extensive side-by-side serologic comparison of BA-3 with the anti- common acute lymphoblastic leukemia antigen (CALLA) monoclonal antibody J-5 was undertaken. Cells examined included established leukemic cell lines, malignant cells from patients with newly diagnosed leukemia/lymphoma, and normal hematopoietic tissues. In all experiments the cellular distribution of the antigens recognized by BA-3 and J-5 were identical when analyzed by immunofluorescent microscopy and the FACS. Iodination of NALM-6 cells, followed by radioimmunoprecipitation and SDS-PAGE, indicated that BA-3 (like J-5) precipitated a glycoprotein of approximately 100,000 daltons. Competitive binding studies using 125I-labeled BA-3 indicated that BA-3 and J-5 were binding to closely associated (if not identical) epitopes on CALLA. Calculation of the equilibrium constant (K value) for BA-3 and J-5, and the approximate number of CALLA molecules per cell, was graphically determined using Scatchard plots. BA-3 and J-5 were shown to have K values of approximately 2.7 x 10(7) M-1 and 7.2 x 10(7) M-1, respectively, with NALM-6 cells expressing 1 x 10(5) to 2 x 10(5) CALLA molecules per cell. Additional studies with BA-3 failed to demonstrate significant antigenic modulation of CALLA in vitro using fresh leukemic cells and leukemic cell lines. Thus, we suggest that antibody affinity may be a significant factor influencing antigenic modulation of CALLA in vitro.

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