of 97a6 positive cells from 1 u00b1 0 5 on day zero of cultivation to more than 60 on the third day of cultivation this proportion then remained approximately constant and declined slightly only toward the end of the 14 day cultivation period fig1 the morphological evaluation of the 97a6 positive cells after may gr u00fcnwald giemsa staining revealed predominantly basophils the rapid rise in the portion of 97a6 positive cells shows that the 97a6 antigen is already being expressed at early stages of basophil development this is also demonstrated by the experiment described in example 3 in which precursor cells of basophils were isolated using the 97a6 antigen this result was also confirmed in example 1 by the fact that 97a6 positive cells could be identified as immature basophilic precursor cells in the peripheral blood of patients with cml in the accelerated phase cells of the basophilic precursor cell line ku 812 were surface labeled with 125 i and subsequently lysed with np 40 the immunoprecipitation was performed with pre assembled 97a6 antibody complexes 97a6 antibodies were immobilized on sepharose beads a bead form of agarose that were conjugated with secondary antibodies as a control immunoprecipitation was performed with beads without 97a6 antibody after boiling the samples in sds under reducing conditions in the presence of 2 mercaptoethanol and under non reducing conditions apparent molecular weights were determined by gel electrophoretical separation on 5 15 polyacrylamide gels laemmli uk nature 227 1970 680 using 14 c methylated marker proteins after autoradiography the result of this immunoprecipitation is shown in fig2 proteins with apparent molecular weights of about 270 kd and about 150 kd can be precipitated with antibody 97a6 under reducing conditions and of about 270 kd under non reducing conditions the protein complex.