to firmly establish the role of il-4 in the directed switch recombination observed in igg1-secreting cells , we have 1 ) used highly purified native il-4 instead of t cell supernatants , 2 ) used resting b cells from f1 mice in which the active igh allele was determined before culture , 3 ) taken advantage of the allelic differences in the restriction fragment lengths of mu , gamma 1 , gamma 2b , and gamma 3 loci to determine the status of the ch genes on both the expressed and unexpressed chromosomes , and 4 ) used different restriction enzymes to distinguish between deletion and rearrangement of a given ch gene .
C1708726
loci
C0008633
chromosomes