The column “Ig expression” shows immunoglobulin class and subclass expression of the light and heavy chain, as determined by immunofluorescence. In column “Fiber FISH,” (V)DJ and class switch deletions are indicated for both alleles separately, indicated with VDJ and CS, respectively. In all cases an allele matching the IgH isotype expression is put in the column “Allele 1,” although in several cases both alleles are matching and the functional allele could not be identified. Presence of (V)DJ recombination, defined as deletion of cosmid U2-2 signal, is indicated with +. In cases HCL12, HCL13, and HCL21 in which the cosmid U2-2 signal is preserved, a deletion between J_H and the proximal DQ52 gene may have occurred, which would be too small to be detected. This would be compatible with the presence of two rearranged J_H bands on Southern blot. In the last column the interpretation of previously described Southern blot analysis25 is shown. Genomic DNA was digested withBamHI, EcoRI, HindIII, BglII, and Sac I and hybridized with probes for J_Hand C_μ. Column “J_H” shows the number of rearranged J_H alleles (R) and column “C_μ” the number of alleles with C_μ-deletions (D). In HCL1 and HCL2, a second rearranged J_H band was found with only one restriction enzyme, which is indicated as 1/2R.

Abbreviations: NE, not evaluable; NT, not tested.

Discordance with fiber FISH results.