furthermore , antigen-sensitive precursors for direct plaque-forming cells , indirect plaque-forming cells , and cluster-forming cells were detected in the spleens of unprimed mice in different frequencies , i.e. , 1 in approximately 10 ( 6 ) , 1 in approximately 7 x 10 ( 6 ) , and 1 in approximately 19 x 10 ( 6 ) spleen cells , respectively .
C0018956
precursors
C0007634
cells